식물의 2차대사산물(테르페노이드, 알칼로이드, 페놀화합물). 2023 nature

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Light regulation of the biosynthesis of phenolics, terpenoids, and alkaloids in plants

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• Review Article
• Open access
• Published: 18 October 2023

Light regulation of the biosynthesis of phenolics, terpenoids, and alkaloids in plants

• Yongliang Liu, 
• Sanjay K. Singh, 
• Sitakanta Pattanaik, 
• Hongxia Wang & 
• Ling Yuan 

Communications Biology volume 6, Article number: 1055 (2023) Cite this article

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Abstract

Biosynthesis of specialized metabolites (SM), including phenolics, terpenoids, and alkaloids, is stimulated by many environmental factors including light. In recent years, significant progress has been made in understanding the regulatory mechanisms involved in light-stimulated SM biosynthesis at the transcriptional, posttranscriptional, and posttranslational levels of regulation. While several excellent recent reviews have primarily focused on the impacts of general environmental factors, including light, on biosynthesis of an individual class of SM, here we highlight the regulation of three major SM biosynthesis pathways by light-responsive gene expression‎, microRNA regulation, and posttranslational modification of regulatory proteins. In addition, we present our future perspectives on this topic.

초록

페놀류, 테르페노이드, 알칼로이드 등

특수 대사산물(SM)의 생합성은

빛을 포함한 여러 환경 요인에 의해 자극을 받습니다.

1) Terpenes 65%

--> 카로티노이드, tetra 카르티노이드(빨강, 주황, 노랑 색소물질)

--> 아르테미시닌(개똥쑥에서 에탄올 추출물, 항말라리아 약물)

2) phenolic 화합물 30%

--> 5k : 케르세틴, 카테킨, 카페인산, 커큐민, 클로로겐산 

--> 3 : 나린진, 리모넨, 레즈베라트롤

--> 안토시아닌,   유제놀

--> 히스페리딘, 페룰산 

3) nitrogen containing metabolite(질소함유 대사산물) 2%

--> 몰핀, 퀴닌(해열제 말라리아 치료제), 빈블라스틴(항암제), 에페드린, 갈란타민(치매치료) 등

4) sulfur containing metabolite 황함유 대사산물 1%

--> 글루코시놀레이트, 알리신, 이소티오시아네이트, 디알릴 설파이드, 설포라판

최근 몇 년 동안

전사, 전사 후, 번역 후 조절 수준에서

빛에 의해 자극된 SM 생합성에 관여하는 조절 메커니즘을 이해하는 데

상당한 진전이 있었습니다.

최근의 여러 우수한 리뷰는

주로 빛을 포함한 일반적인 환경 요인이

개별 SM 종류의 생합성에 미치는 영향에 초점을 맞추었지만,

여기서는

빛에 반응하는 유전자 발현,

마이크로RNA 조절 및 조절 단백질의 전사 후 변형에 의한

세 가지 주요 SM 생합성 경로의 조절을 강조합니다.

또한 이 주제에 대한 향후 전망을 제시합니다.

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Introduction

Light is a crucial environmental factor that significantly impacts the growth, development, and metabolism in plants. It serves as the primary energy source for photosynthesis while acting as a complex signaling input that modulates plant physiology and development1. The perception of light signal and the molecular mechanism by which light regulates developmental and metabolic pathways have been extensively studied in the model plant Arabidopsis. Plants use different photoreceptors to perceive various wavelengths of light. The major photoreceptors include phytochromes, cryptochromes, and the UV Resistance Locus 8 (UVR8). Phytochromes (PHYA-PHYE) perceive red and far-red light, cryptochromes (CRY1 and CRY2) sense blue/UV-A light, and UVR8 detects UV-B light1,2,3,4,5,6. Upon perception of different wavelengths of light, these photoreceptors become activated and transmit signals to downstream components, which consist of transcriptional activators and repressors that regulate diverse light-induced biological processes. The most well-characterized light signaling components include the Phytochrome Interacting Factors (PIFs), Elongated Hypocotyl 5 (HY5), the B-box proteins (BBX), Constitutive Photomorphogenic 1 (COP1), Suppressor of PHYA-105 (SPA), and De-Etiolated 1(DET1)3,4,5,7,8,9.

PIFs are a group of basic helix-loop-helix (bHLH) transcription factors (TFs) that accumulate in the dark and act as repressors of light signaling by inhibiting the expression‎ of light-responsive genes. However, under light conditions, the activated phytochromes directly interact with PIFs, leading to the phosphorylation, ubiquitination, and proteasomal degradation of PIFs4,5. Like phytochromes, cryptochromes directly interact with PIFs to regulate their activities on target genes10. HY5, a basic leucine-zipper (bZIP) TF, is an activator of different light responses mediated by phytochromes, cryptochromes, and UVR8. HY5 acts synergistically or antagonistically with PIFs to regulate the expression‎ of light-responsive genes in developmental and metabolic pathways in Arabidopsis1,8. For instance, HY5 and PIF3 collaboratively regulate anthocyanin biosynthesis11, whereas HY5 and PIF1 act antagonistically to regulate carotenoid and chlorophyll pathway genes12.

소개

빛은

식물의 성장, 발달, 신진대사에 큰 영향을 미치는

중요한 환경 요인입니다.

빛은

광합성을 위한 주요 에너지원인 동시에

식물의 생리와 발달을 조절하는 복잡한 신호 입력으로 작용합니다1.

빛 신호의 인식과 빛이 발달 및 대사 경로를 조절하는 분자 메커니즘은

모델 식물인 애기장대에서 광범위하게 연구되어 왔습니다.

식물은

다양한 파장의 빛을 감지하기 위해

다양한 광수용체를 사용합니다.

주요 광수용체에는 피토크롬, 크립토크롬, 자외선 저항성 유전자좌 8(UVR8)이 있습니다. 피토크롬(PHYA-PHYE)은 적색 및 원적색 빛을, 크립토크롬(CRY1 및 CRY2)은 청색/UV-A 빛을, UVR8은 UV-B 빛을 감지합니다1,2,3,4,5,6. 다양한 파장의 빛을 감지하면 이러한 광수용체가 활성화되어 빛을 통해 유도되는 다양한 생물학적 과정을 조절하는 전사 활성화제와 억제제로 구성된 하위 구성 요소에 신호를 전달합니다.

가장 잘 알려진 빛 신호 성분으로는

피토크롬 상호 작용 인자(PIF),

길쭉한 엽록소 5(HY5),

B-박스 단백질(BBX),

구성적 광모양 생성 1(COP1),

PHYA-105 억제제(SPA),

디 에티올화된 1(DET1)3,4,5,7,8,9이 있습니다.

PIF는

어둠 속에서 축적되어 빛에 반응하는 유전자의 발현을 억제함으로써

빛 신호의 억제자 역할을 하는 기본 나선 루프 헬릭스(bHLH) 전사인자(TF)의 그룹입니다.

그러나

빛이 있는 조건에서는

활성화된 피토크롬이 PIF와 직접 상호 작용하여

PIF의 인산화, 유비퀴틴화 및 프로테아좀 분해를 유도합니다4,5.

피토크롬과 마찬가지로

크립토크롬도

PIF와 직접 상호 작용하여

표적 유전자에 대한 활동을 조절합니다10 .

기본 류신 지퍼(bZIP) TF인 HY5는

피토크롬, 크립토크롬 및 UVR8에 의해 매개되는 다양한 빛 반응의 활성화제입니다.

HY5는

애기장대의 발달 및 대사 경로에서 빛에 반응하는 유전자의 발현을 조절하기 위해

PIF와 상승적 또는 길항적으로 작용합니다1,8.

예를 들어,

HY5와 PIF3는

안토시아닌 생합성을 협력적으로 조절하는 반면11,

HY5와 PIF1은 길항적으로 작용하여

카로티노이드 및 엽록소 경로 유전자를 조절합니다12.

The stabilities of PIFs and HY5 are regulated by COP1/SPA and DET1, which are components of the E3 ubiquitin ligase complexes13. COP1, SPA, and DET1 are repressors of light-mediated responses in plants7,13,14. The E3 ligase activity of COP1 depends on its interaction with SPA13. In the dark, active COP1/SPA and DET1 contribute to the ubiquitination and degradation of HY5, while promoting the stability of PIFs13. However, in the presence of light, the active photoreceptors suppress COP1/SPA and DET1 activity, resulting in the stabilization of HY5 and degradation of PIFs13,15,16. A recent study suggests that DET1 physically interacts with COP1. DET1 mediates the COP1-HY5 interaction and is necessary for the destabilization of COP1 in a light-independent manner. DET1-mediated COP1 destabilization is necessary for HY5 degradation13. The BBX proteins belong to a subfamily of zinc finger TFs with one or two B-box domains at the N-termini. BBX proteins play diverse roles in regulating light signaling through interactions with HY5 and PIFs17. In addition to HY5, both COP1 and DET1 are involved in targeting BBX proteins for degradation in darkness18,19.

Plants synthesize more than 200,000 chemically diverse specialized metabolites (SM)20. Many SM serve as chemical defenses to protect plants from various biotic and abiotic stresses. In addition, many of these SMs are valued for their inherent therapeutic properties that are beneficial to human health. Light plays a pivotal role in the biosynthesis of an array of SM. Several excellent reviews have covered effects of light on biosynthesis of an individual class of SM such as anthocyanins21,22. Zhang et al.21 summarize the effects of light quality and intensity on gene expression‎ and metabolite accumulation, while Hashim et al22 highlight the use of artificial light sources to elicit SM production in in vitro cultured medicinal plants. However, these reviews have not delved into the underlying regulatory mechanisms that govern SM biosynthesis in response to light. Two recent reviews have included brief summaries of light regulation of anthocyanin biosynthesis in plants23,24.

PIF와 HY5의 안정성은

E3 유비퀴틴 리가제 복합체의 구성 요소인 COP1/SPA 및 DET1에 의해 조절됩니다13 .

COP1, SPA 및 DET1은

식물에서 빛 매개 반응의 억제제입니다7,13,14.

COP1의 E3 리가제 활성은

SPA와의 상호 작용에 따라 달라집니다13.

어둠 속에서 활성 COP1/SPA 및 DET1은

HY5의 유비퀴틴화 및 분해에 기여하는 동시에 PIF의 안정성을 촉진합니다13 .

그러나 빛이 있으면 활성 광수용체는 COP1/SPA 및 DET1 활성을 억제하여 HY5의 안정화와 PIF의 분해를 초래합니다13,15,16. 최근 연구에 따르면 DET1은 COP1과 물리적으로 상호작용하는 것으로 나타났습니다. DET1은 COP1-HY5 상호 작용을 매개하며 빛에 독립적인 방식으로 COP1의 불안정화에 필요합니다. DET1을 매개로 한 COP1 불안정화는 HY5 분해에 필요합니다13. BBX 단백질은 N-말단에 하나 또는 두 개의 B-박스 도메인을 가진 아연 핑거 TF의 하위 계열에 속합니다. BBX 단백질은 HY5 및 PIF와의 상호작용을 통해 빛 신호를 조절하는 다양한 역할을 합니다17 . HY5 외에도 COP1과 DET1은 어둠 속에서 BBX 단백질을 표적으로 하여 분해하는 데 관여합니다18,19.

식물은

화학적으로 다양한 20만 개 이상의

특수 대사산물(SM)을 합성합니다20.

많은 SM은

다양한 생물학적 및 비생물학적 스트레스로부터

식물을 보호하는 화학적 방어 역할을 합니다.

또한

이러한 SM 중 다수는

인체 건강에 유익한 고유의 치료적 특성으로 인해 가치가 높습니다.

빛은

다양한 SM의 생합성에서 중추적인 역할을 합니다.

안토시아닌21,22 과 같은 개별 SM의 생합성에 대한

빛의 영향을 다룬 여러 훌륭한 리뷰가 있습니다.

Zhang등21은

빛의 품질과 강도가 유전자 발현과 대사산물 축적에 미치는 영향을 요약하고,

Hashim 등22은 시험관 배양 약용 식물에서 SM 생산을 유도하기 위해

인공 광원을 사용하는 것을 강조합니다.

그러나

이러한 리뷰에서는

빛에 반응하여 SM 생합성을 지배하는 근본적인 조절 메커니즘에 대해서는 자세히 다루지 않았습니다.

최근 두 개의 리뷰에서

식물의 안토시아닌 생합성에 대한 빛의 조절에 대한 간략한 요약이 포함되어 있습니다23,24.

In this review, we delve into the light regulation of three major groups of SM:

phenolic compounds (e.g., anthocyanins and stilbenes),

terpenes (e.g., carotenoids and artemisinin), and

alkaloids and nitrogen-containing metabolites (e.g., terpenoid indole alkaloids; steroidal glycoalkaloids and glucosinolates) (Fig. 1).

Transcriptional regulation has emerged as the major mechanism governing the biosynthesis of SM25. Here, we summarize recent advancements in understanding the transcriptional regulation of selected SM influenced by light. In addition to transcriptional regulation, fine-tuning the accumulation of SM in plants involves post-transcriptional (e.g., microRNA/small RNA)26,27,28,29 and post-translational (e.g., protein phosphorylation and ubiquitination)30,31,32 regulatory mechanisms. We thus aim to highlight the influence of light on post-transcriptional and post-translational regulation of SM, with a particular emphasis on phenolic compounds such as anthocyanin. In addition, we discuss the future prospect and emerging areas of SM biosynthesis in plants.

이 리뷰에서는

페놀 화합물(예: 안토시아닌 및 스틸벤),

테르펜(예: 카로티노이드 및 아르테미시닌),

알칼로이드 및 질소 함유 대사산물(예: 테르페노이드 인돌 알칼로이드, 스테로이드계 글리코알칼로이드 및 글루코시놀산염)의

세 가지 주요 SM 그룹의 광 조절에 대해 자세히 알아봅니다(그림 1).

폴리페놀 화합물의 일종인 안토시아닌은 노화 방지 및 항염증 등 다양한 건강상의 이점을 제공하는 것으로 밝혀졌습니다. 이 전향적 코호트 연구는 미국에서 안토시아닌의 식이 섭취와 모든 원인에 의한 사망률 및 심혈관 질환 사망률의 관계를 조사하는 것을 목표로 합니다. 이 연구의 목적은 안토시아닌 섭취와 심혈관 질환뿐만 아니라 모든 원인으로 인한 사망률 사이의 가능한 상관관계를 탐구하는 것이었습니다. 2019년 12월 31일까지의 퍼블릭 액세스 NHANES 연계 국가 사망 지수 파일을 기반으로 사망률 현황과 심장 질환별 사망 원인을 확인했습니다. 안토시아닌 섭취가 사망률 결과에 미치는 영향을 평가하기 위해 다변량 콕스 회귀 분석을 사용하여 다양한 인구학적 특성, 생활습관 요인 및 동반 질환을 조정하여 위험률과 95% 신뢰구간을 생성했습니다. 또한 카플란-마이어 생존 곡선, 하위 그룹 분석도 활용했습니다. 다양한 시나리오에서 제한된 입방 스플라인 모델을 사용하여 식이 안토시아닌 섭취량을 평가했습니다. 총 11,959명의 참가자가 최종 코호트를 완료했으며, 평균 연령은 47.12세(SD ± 0.35)였습니다. 여러 변수를 조정한 결과, 최상위 사분위수의 안토시아닌 섭취량과 모든 사망 원인 간에 역관계가 확인되었으며, 위험비(HR)는 0.68(95% CI: 0.52-0.89)로 나타났습니다. 마찬가지로 안토시아닌 섭취량 증가는 심장 질환 사망률 감소와 관련이 있었으며, HR은 0.61(95% CI: 0.38-0.97)이었습니다. 또한 용량-반응 곡선에서는 안토시아닌 섭취량이 증가함에 따라 모든 원인에 의한 사망률과 심혈관 질환에 의한 사망률 모두 일관되게 감소하는 것으로 나타났습니다. 추가 하위 그룹 분석 결과, 안토시아닌 섭취량 증가는 백인과 남성의 모든 원인에 의한 사망률 감소와 관련이 있는 것으로 나타났습니다. 또한 안토시아닌을 많이 섭취하는 것은 고혈압이나 고지혈증 상태와 관계없이 모든 원인에 의한 사망률 감소와 유의미한 상관관계가 있는 것으로 나타났습니다. 이번 연구는 안토시아닌의 적절한 식이 섭취가 전체 사망률 감소와 관련이 있음을 시사합니다. 또한, 안토시아닌 섭취와 심혈관 질환으로 인한 사망률 감소 사이에 상당한 연관성이 있는 것으로 나타나 안토시아닌이 심혈관 관련 사망 위험을 효과적으로 낮출 수 있음을 시사합니다.

전사 조절은 SM25 의 생합성을 지배하는 주요 메커니즘으로 부상했습니다. 여기에서는 빛의 영향을 받는 일부 SM의 전사 조절을 이해하는 데 있어 최근의 진전을 요약합니다. 전사 조절 외에도 식물에서 SM의 축적을 미세 조정하는 데는 전사 후(예: 마이크로RNA/소형 RNA)26,27,28,29 및 번역 후(예: 단백질 인산화 및 유비퀴틴화)30,31,32 조절 메커니즘이 포함됩니다. 따라서 우리는 안토시아닌과 같은 페놀 화합물에 특히 중점을 두고 SM의 전사 후 및 번역 후 조절에 대한 빛의 영향을 강조하는 것을 목표로 합니다. 또한 식물의 SM 생합성의 미래 전망과 새롭게 떠오르는 분야에 대해서도 논의합니다.

Fig. 1: Light regulation of the biosynthesis of plant specialized metabolites (SM).

Light affects the biosynthesis of phenolics (anthocyanins and stilbenes), terpenes (carotenoids and artemisinin), alkaloids, and other nitrogen-containing compounds (vindoline, camptothecin, steroidal glycoalkaloids, and glucosinolates) in plants. Certain SM, such as carotenoids and anthocyanins, are produced in a wide range of plants, while others, such as vindoline and camptothecin, are species-specific. The representative plant species include Arabidopsis thaliana (Arabidopsis), Artemisia annua (Sweet Wormwood), Carica papaya (Papaya), Citrus sinensis (Citrus), Camptotheca acuminata (Chinese Happy Tree), Capsicum annuum (Pepper), Catharanthus roseus (Madagascar Periwinkle), Fragaria ananassa (Strawberry), Fortunella crassifolia (Sweet Kumquat), Malus x domestica (Apple), Pyrus pyrifolia (Pear), Prunus persica (Peach), Solanum lycopersicum (Tomato), and Vitis vinifera (Grape).

빛은 식물에서 페놀류(안토시아닌 및 스틸벤), 테르펜(카로티노이드 및 아르테미시닌), 알칼로이드 및 기타 질소 함유 화합물(빈돌린, 캠토테신, 스테로이드성 글리코알칼로이드 및 글루코시놀레이트)의 생합성에 영향을 미칩니다. 카로티노이드 및 안토시아닌과 같은 특정 SM은 다양한 식물에서 생성되는 반면, 빈돌린 및 캠토테신과 같은 다른 SM은 종에 따라 다릅니다.

대표적인 식물 종으로는 애기장대(Arabidopsis thaliana ), 쑥( Artemisia annua ), 파파야( Carica papaya ), 감귤류( Citrus sinensis ), 중국 행복나무( Camptotheca acuminata ), 고추( Capsicum annuum ) 등이 있습니다, Catharanthus roseus (마다가스카르 대수리), Fragaria ananassa (딸기), Fortunella crassifolia (달콤한 금귤), Malus x domestica (사과), Pyrus pyrifolia (배), Prunus persica (복숭아), Solanum lycopersicum (토마토), Vitis vinifera (포도).

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Phenolic compounds: transcriptional, post-transcriptional, and post-translational regulation of anthocyanin biosynthesis in response to light

Anthocyanins are a diverse group of phenolic compounds that serve various biological functions and are accumulated in abundance in flowers, fruits, and vegetables (Fig. 1). Anthocyanins play crucial roles in plant growth, development, and reproduction, and they also provide health benefits to humans33. The biosynthesis of anthocyanins has been extensively studied across a wide range of plant species. Anthocyanins are synthesized through the phenylpropanoid pathway in which phenylalanine acts as the primary precursor for all flavonoids, including anthocyanins (Fig. 2a). Phenylalanine undergoes a series of enzymatic reactions to produce coumaroyl-CoA. One coumaroyl-CoA molecule condenses with three malonyl Co-A molecules, catalyzed by chalcone synthase (CHS), to produce naringenin chalcone. Subsequently, chalcone isomerase (CHI) isomerizes naringenin chalcone to form flavanones. Flavanones are then converted to dihydroflavonols by flavanone 3-hydroxylase (F3H) and further reduced to leucoanthocyanidins by dihydroflavonol reductase (DFR). The leucoanthocyanidins are converted to anthocyanidins by leucoanthocyanidin dioxygenase/anthocyanidin synthase (LDOX/ANS)34. The expression‎ of anthocyanin biosynthetic genes is primarily regulated by the MYB-bHLH-WD40 (MBW) TF complex, formed by the R2R3MYB, bHLH, and WD40 proteins. In Arabidopsis, the well-studied members of the MBW complex include the R2R3MYBs, Production of Anthocyanin Pigment 1/2 (PAP1/PAP2), the bHLH TFs, Glabrous 3/Enhancer of Glabrous 3/ Transparent Testa 8 (GL3/EGL3/TT8), and the WD40 protein, Transparent Testa Glabra1 (TTG1)24,35,36. TF families of AP2/ERFs (Apetala2/Ethylene Response Factors), WRKY, bZIP, and R3MYB have also been identified as regulators of anthocyanin biosynthesis23,24,35,36. Light influences anthocyanin biosynthesis through regulating the individual TFs in the MBW complex or the associated upstream TFs. Key TFs involved in the light signaling pathway, such as HY5, BBX, and PIFs, are the major regulators of anthocyanin biosynthesis as they affect the MBW complex. Here, we discuss transcriptional, post-transcriptional (miRNA), and post-translational (phosphorylation/ubiquitination) regulation of anthocyanin biosynthesis under the influence of light (Figs. 2 and 3).

안토시아닌은

다양한 생물학적 기능을 하는 다양한 페놀 화합물 그룹으로

꽃, 과일, 채소에 풍부하게 축적되어 있습니다(그림 1).

안토시아닌은

식물의 성장, 발달 및 번식에 중요한 역할을 하며,

인간에게도 건강상의 이점을 제공합니다33.

안토시아닌의 생합성은 다양한 식물 종에 걸쳐 광범위하게 연구되어 왔습니다.

안토시아닌은

페닐알라닌이 안토시아닌을 포함한 모든 플라보노이드의 주요 전구체 역할을 하는

페닐프로파노이드 경로를 통해 합성됩니다(그림 2a).

페닐알라닌은 일련의 효소 반응을 거쳐

쿠마로일-CoA를 생성합니다.

쿠마로일-CoA 분자 하나가

칼로콘 신타제(CHS)에 의해 촉매된 3개의 말로닐 Co-A 분자와 응축되어

나린게닌 칼콘을 생성합니다.

그 후 칼콘 이성질화 효소(CHI)가

나린게닌 칼콘을 이성질화하여

플라바논을 형성합니다.

그런 다음 플라바논은

플라바논 3-하이드록실라제(F3H)에 의해 디하이드로플라보놀로 전환되고

디하이드로플라보놀 환원효소(DFR)에 의해 류코안토시아니딘으로 다시 환원됩니다. 류

코안토시아니딘은 류코안토시아니딘 디옥시게나제/안토시아니딘 신타제(LDOX/ANS)34 에 의해 안토시아니딘으로 전환됩니다. 안토시아닌 생합성 유전자의 발현은 주로 R2R3MYB, bHLH 및 WD40 단백질에 의해 형성되는 MYB-bHLH-WD40(MBW) TF 복합체에 의해 조절됩니다. 애기장대에서 잘 연구된 MBW 복합체의 구성원으로는 안토시아닌 색소 1/2 생성(PAP1/PAP2), bHLH TF, 글랩브로스 3/글랩브로스 3/투명 테스타 8(GL3/EGL3/TT8), WD40 단백질인 투명 테스타 글랩브라1(TTG1)24,35,36이 있습니다. 안토시아닌 생합성의 조절 인자로는 AP2/ERF(Apetala2/에틸렌 반응 인자), WRKY, bZIP 및 R3MYB의 TF 계열도 확인되었습니다23,24,35,36. 빛은 MBW 복합체의 개별 TF 또는 관련 업스트림 TF를 조절하여 안토시아닌 생합성에 영향을 미칩니다. HY5, BBX, PIF와 같이 빛 신호 경로에 관여하는 주요 TF는 MBW 복합체에 영향을 미치는 안토시아닌 생합성의 주요 조절 인자입니다. 여기에서는 빛의 영향을 받는 안토시아닌 생합성의 전사, 전사 후(miRNA) 및 번역 후(인산화/유비퀴틴화) 조절에 대해 설명합니다(그림 2 및 3).

Fig. 2: Transcriptional regulation of anthocyanin biosynthesis in Arabidopsis and apple in response to light.

a Schematic diagram of the anthocyanin biosynthetic pathway in plants.

The light-responsive genes encoding anthocyanin biosynthetic pathway enzymes are highlighted red. PAL phenylalanine ammonia-lyase, C4H cinnamate 4-hydroxylase, 4CL 4-coumarate: CoA ligase, CHS chalcone synthase, CHI chalcone isomerase, F3H flavanone 3-hydroxylase, F3′H flavonoid 3′-hydroxylase, F3′5′H flavonoid 3′,5′-hydroxylase, DFR dihydroflavonol reductase, ANS/LDOX anthocyanin synthase (leucoanthocyanidin dioxygenase), UFGT UDP-glucose: flavonoid 3-O-glucosyltransferase. The regulations of anthocyanins in Arabidopsis (b) and apple (c) share significant regulatory mechanisms that are conferred by conserved transcription factors; however, additional characterized regulatory factors are only found in apples. In Arabidopsis and apple (Malus domestica), anthocyanin biosynthesis is regulated by transcriptional activators such HY5, BBXs, and the MYB-bHLH-WD40 (MBW) complex, as well as the repressors COP1, DET1, and PIFs. These regulatory factors act downstream of the photoreceptors (UVR8, Phytochromes, and Cryptochromes). HY5 plays a central role in the regulation by activating the expression‎ of the MYB factors (PAP1 in Arabidopsis and MdMYB1/10 in apple) in the MBW complex. HY5 also regulates the expression‎ of the bHLH factors (TT8/EGL3/GL3 in Arabidopsis and MdbHLH3/33 in apple) in the MBW complex through two other MYBs. BBXs differentially regulate HY5 activity to modulate anthocyanin biosynthesis. PIFs act as activators or repressors in the process. PIFs regulate anthocyanin biosynthesis either by targeting PAP1 or the pathway genes. In apple, two additional activators, MdbZIP44 and MdERF38, are involved in MdPIF7-mediated anthocyanin biosynthesis. Furthermore, three apple WRKYs are involved in the regulation of anthocyanin biosynthesis by activating HY5, MdMYB1/10 or pathway genes.

식물에서 안토시아닌 생합성 경로의 모식도.

안토시아닌 생합성 경로 효소를 코딩하는 빛에 반응하는 유전자는 빨간색으로 강조 표시되어 있습니다. PAL 페닐알라닌 암모니아 분해 효소, C4H 시나메이트 4-하이드록실라제, 4CL 4-쿠마레이트: CoA 리가제, CHS 칼콘 신타제, CHI 칼콘 이소머라제, F3H 플라바논 3-하이드록실라제, F3′H 플라보노이드 3′-하이드록실라제, F3′5′H 플라보노이드 3′, 5′- 하이드 록실 라제, DFR 디 하이드로 플라보놀 환원 효소, ANS / LDOX 안토시아닌 신타 제 (류코 안토시아니딘 디 옥시 제), UFGT UDP 글루코스: 플라보노이드 3-O- 글루코실 트랜스퍼라제.

애기장대(b)와 사과(c)의 안토시아닌 조절은 보존된 전사 인자에 의해 부여되는 중요한 조절 메커니즘을 공유하지만, 추가로 특징적인 조절 인자는 사과에서만 발견됩니다. 애기장대와 사과(말루스 도메스티카)에서 안토시아닌 생합성은 HY5, BBX, MYB-bHLH-WD40(MBW) 복합체와 같은 전사 활성화 인자와 억제 인자인 COP1, DET1, PIF에 의해 조절됩니다. 이러한 조절 인자들은 광수용체(UVR8, 피토크롬, 크립토크롬)의 하류에서 작용합니다. HY5는 MBW 복합체에서 MYB 인자(애기장대의 PAP1, 사과의 MdMYB1/10)의 발현을 활성화하여 조절의 중심 역할을 합니다. HY5는 또한 두 개의 다른 MYB를 통해 MBW 복합체에서 bHLH 인자(애기장대에서는 TT8/EGL3/GL3, 사과에서는 MdbHLH3/33)의 발현을 조절합니다. BBX는 HY5 활성을 차등적으로 조절하여 안토시아닌 생합성을 조절합니다. PIF는 이 과정에서 활성화제 또는 억제제 역할을 합니다. PIF는 PAP1 또는 경로 유전자를 표적으로 삼아 안토시아닌 생합성을 조절합니다. 사과에서는 두 개의 추가 활성화 인자인 MdbZIP44와 MdERF38이 MdPIF7 매개 안토시아닌 생합성에 관여합니다. 또한, 세 개의 사과 WRKY는 HY5, MdMYB1/10 또는 경로 유전자를 활성화하여 안토시아닌 생합성 조절에 관여합니다.

bZIP44 BASIC LEUCINE ZIPPER 44, BBX B-box proteins, COP1 CONSTITUTIVE PHOTOMORPHOGENIC 1, DET1 DE-ETIOLATED 1, EGL3 ENHANCER OF GLABRA 3, GL3 GLABRA 3, HY5 ELONGATED HYPOCOTYL5, ERF38 ETHYLENE RESPONSE FACTOR 38, PAP1 PRODUCTION OF ANTHOCYANIN PIGMENT 1, PIFs PHYTOCHROME INTERACTING FACTORs, TT8 TRANSPARENT TESTA 8, TTG1 TRANSPARENT TESTA GLABRA 1, UVR8 UV-RESISTANCE LOCUS8. Solid arrows indicate direct regulation, and the dotted arrows refer to indirect regulation. Solid T-bars and dotted T-bars indicate direct and indirect repression, respectively.

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Fig. 3: Posttranscriptional and posttranslational regulation of specialized metabolite biosynthesis in response to light.

a Light and miRNA-mediated regulatory network of anthocyanin biosynthesis. Light induces the expression‎ of several transcription factors (including HY5, MYB1, and PIFs) and miRNAs (miR858, miR7125, and miR156). The expression‎ of miRNAs is differentially regulated by HY5, MYB1, and PIFs. MYB1 positively regulates the MBW complex, while HY5 represses the MBW repressor MYBL2. The light-inducible miR156 positively regulates MBW by repressing the repressor SPL9. MYB16, an activator of lignin pathway gene CCR, also represses MBW, thus maintaining the homeostasis between anthocyanin and lignin in response to light. b Light and protein kinase-mediated regulatory network of anthocyanin biosynthesis. Light induces the expression‎ of MAP kinases (MPK4 and MPK6) which phosphorylate HY5, as well as PAP and MYB1, positively regulating anthocyanin biosynthesis. The kinase SnRK1, a negative regulator of the MBW complex, is suppressed by light. Phosphorylation of the components in the MBW complex leads to its dissociation and degradation, resulting in reduced anthocyanin accumulation. CCR CINNAMOYL-CoA REDUCTASE. MPK4 Mitogen-Activated Protein Kinase 4, MPK6 Mitogen-Activated Protein Kinase 6, PAP1 PRODUCTION OF ANTHOCYANIN PIGMENT 1, PIFs PHYTOCHROME INTERACTING FACTORs, SnRK1 SNF1-related protein kinase 1, SPL9 SQUAMOSA PROMOTER BINDING PROTEIN-LIKE9, CCR Cinnamoyl-CoA reductase, WD40,TRANSPARENT TESTA GLABROUS1. The arrows and T-bars represent positive and negative regulation, respectively. The double-headed arrows indicate the physical interactions between kinases and their target proteins. The phosphate moieties (P) with a positive effect on regulation are depicted in yellow while those with a negative effect are in red.

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HY5 is a key regulator of light-induced anthocyanin biosynthesis in various plant species, and it acts downstream of multiple photoreceptors, such as PHY, CRY, and UVR8, in the signal transduction pathways37. In the presence of light, the activated photoreceptors inhibit COP1/SPA activity by distinct regulatory mechanisms, leading to the stabilization of HY538. HY5 activates the expression‎ of anthocyanin pathway genes, such as CHS, DFR, and LDOX, as well as regulatory genes (such as MYBs) by directly binding to the G-box or ACE (ACGT-rich elements) motifs in the promoters of the target genes. In Arabidopsis, HY5 regulates anthocyanin biosynthesis directly by binding to the promoters of pathway genes and indirectly by activating the expression‎ of PAP1 (MYB75)39 and the MYB-like domain TF MYBD40. HY5 binds to the MYBD and PAP1 promoter to induce expression‎ in response to light. MYBD or PAP1 overexpression‎ induces the expression‎ of anthocyanin pathway genes such as DFR and ANS. MYBD represses the activity of MYBL2, a negative regulator of anthocyanin biosynthesis, resulting in the promotion of anthocyanin biosynthesis40 (Fig. 2b). Similar to Arabidopsis, in apple (Malus domestica), MdHY5 stimulates anthocyanin biosynthesis by inducing the expression‎ of MdMYB10 and MdMYBDL1, and HY5 directly bind to the G-box motifs in these MYB promoters41,42. In apple, MdMYB1/10 are PAP1-like MYBs and components of the apple MBW complex, and MYBDL1 is closely related to Arabidopsis MYBD. MdHY5 and MdMYBDL1 inhibit the expression‎ of MdMYB16 and MdMYB308, which are repressors of anthocyanin accumulation. Additionally, MdMYB308 interacts with MdbHLH3 and MdbHLH33, components of the apple MBW complex. MdMYB308-MdbHLH3/33 interaction likely affects MBW complex formation and influences anthocyanin accumulation in response to light42 (Fig. 2c). Exposure to UV-B induces anthocyanin accumulation in apple. Recent studies identified two UV-B responsive WRKY TFs, MdWRKY71-L and MdWRKY72, that promote anthocyanin accumulation in apple by inducing the expression‎ of MdHY5 and MdMYB143,44. In blood orange (Citrus x sinensis), HY5 regulates the expression‎ of the MYB TF Ruby to promote anthocyanin accumulation45. In peach (Prunus persica), PpHY5 regulates the expression‎ of biosynthetic genes, such as PpCHS1, PpCHS2, PpDFR1, and regulatory gene PpMYB10.1 to induce anthocyanin accumulation46. In red-skinned pears (Pyrus pyrifolia), PyHY5 directly binds to the G-box element in the promoters of PyMYB10 and PyWD40, thereby enhancing their expression‎ and resulting in increased anthocyanin accumulation47. SlHY5 regulates blue-light-induced anthocyanin accumulation by directly binding to the CHS and DFR promoters in tomato37.

In Arabidopsis, PIF3 positively, while PIF4 and PIF5 negatively, regulate anthocyanin biosynthesis in response to different light conditions (Fig. 2b). HY5 acts synergistically or antagonistically with PIFs to regulate different biological processes. Overexpression‎ of PIF3 (PIF3-OE) increases anthocyanin levels under far-red light, while pif3 mutants exhibit reduced anthocyanin accumulation. However, the anthocyanin level in the hy5 mutant overexpressing PIF3 (PIF3-OEhy5) is similar to that in the hy5 single mutant, suggesting that the positive effects of PIF3 require a functional HY5. Indeed, PIF3 and HY5 activate the same set of genes in the anthocyanin biosynthetic pathway, and PIF3-mediated activation is dependent on HY5. However, PIF3 and HY5 do not compete for the same binding motif. PIF3 binds to the G/E-box, while HY5 binds to ACE motifs in the promoters of anthocyanin pathway genes11. In Arabidopsis, red light induces anthocyanin accumulation, which is enhanced in pif4 and pif5 mutants but suppressed in PIF4-OE and PIF5-OE plants. Consistent with anthocyanin phenotype, the expression‎ of genes encoding anthocyanin pathway enzymes and regulators, such as CHS, F3′H, DFR, LDOX, PAP1, and TT8, is increased in pif4 and pif5 mutants but decreased in PIF4 and PIF5-OE plants. Additionally, PIF4 and PIF5 repress red light-induced promoter activities of DFR and F3’H, and PIF5 binds to the G-box motif in the DFR promoter to repress its expression‎. These findings collectively suggest that PIF4 and PIF5 act as negative regulators of red light-induced anthocyanin accumulation48. A recent study demonstrated that PIF4 binds to the G-box motif in the PAP1 promoter to repress its expression‎ and negatively regulates anthocyanin biosynthesis in response to white light49. Anthocyanin accumulation is also suppressed in response to other abiotic factors such as salt and phytohormone BA (6-benzylaminopurine). It has been demonstrated that PIF4 interacts with the R2R3 MYB TF PAP1 and competes with the bHLH TF TT8 for binding to PAP1, thus inhibiting the formation of the MBW complex. This mechanism is likely involved in PIF4 and PIF5 inhibition of anthocyanin accumulation in red light50. The function of HY5 in PIF4/5-mediated anthocyanin biosynthesis is not explored in these studies. PIFs also negatively regulate anthocyanin accumulation in other plants such as apple and pear. PIF8 positively regulates anthocyanin biosynthesis in pear skin and calli by activating the expression‎ of CHS51. In apple, MdPIF7 is a negative regulator, while MdHY5 and MdBBX23 are positive regulators of anthocyanin biosynthesis. MdHY5 is regulated by MdBBX23. MdPIF7 interacts with MdBBX23 and attenuates the transcriptional activation of MdBBX23 on MdHY5, thereby repressing anthocyanin accumulation. In apple MdbZIP44 and MdERF38 interact with MdMYB1 to regulate anthocyanin biosynthesis. MdPIF7 interacts with MdERF38 and MdbZIP44 and weakens the formation of the MdERF38/MdbZIP44-MdMYB1 complex to affect anthocyanin accumulation (Fig. 2c)52.

The B-box (BBX) proteins regulate anthocyanin biosynthesis in response to light either independently or by interacting with HY553,54. In Arabidopsis, anthocyanin biosynthesis is positively regulated by BBX21/22/2318,55 but generally negatively regulated by BBX24/2556 (Fig. 2b). In apple (Malus domestica), while a group of light-inducible BBX proteins (BBX1/20/21/22/33) promote anthocyanin biosynthesis by regulating the expression‎ of HY5 and MYB1/1057,58, MdBBX37 inhibits anthocyanin biosynthesis through two different mechanisms (Fig. 2c). MdBBX37 interacts with MdMYB1 and MdMYB9, preventing them from binding to the promoters of the anthocyanin pathway genes. Alternatively, MdBBX37 binds to the MdHY5 promoter to repress its expression‎59. Similar to apple, a number of BBX proteins regulate anthocyanin accumulation in pear (Pyrus pyrifolia). PpBBX16 and PpBBX18 interact with PpHY5 to activate the expression‎ of PpMYB10 and anthocyanin pathway genes to regulate anthocyanin accumulation. PpBBX21, on the other hand, acts as a negative regulator by inhibiting the formation of the PpBBX18–PpHY5 complex, thus repressing anthocyanin biosynthesis60,61. In strawberry (Fragaria x ananassa), FaBBX22 interacts with FaHY5 to enhance anthocyanin accumulation, and the interaction upregulates the expression‎ of anthocyanin biosynthetic genes such as FaPAL, FaANS, FaF30H, and FaUFGT1, as well as the transporter FaRAP, in a light-dependent manner62. In summary, light-induced anthocyanin biosynthesis is regulated by a well-conserved group of TFs, i.e. PIFs, HY5, BBX, and MYBs in Arabidopsis and their homologs in other plant species, such as apple, pear, and strawberry. In addition, other regulators, such as WRKYs and the AP2/ERFs, have been identified in apple as the regulators of anthocyanin biosynthesis.

MicroRNAs (miRNAs) are a class of endogenous small RNAs, typically 21 or 22 nucleotides in length, found in both animals and plants63. They are important mediators of post-transcriptional gene regulation that fine-tune many developmental and metabolic processes in plants. MiRNAs are known to regulate biosynthesis of SM, including anthocyanins in Arabidopsis and other plant species28,29,64,65,66, terpenoid indole alkaloids (TIAs) in Catharanthus roseus26, and sesquiterpenes in Arabidopsis67. In this context, we will specifically discuss the influence of light on miRNA regulation of anthocyanin biosynthesis in plants.

In Arabidopsis, the expression‎ of miR858a, a positive regulator of anthocyanin biosynthesis, is induced by light. Light-induced expression‎ of miR858a is HY5-dependent, and HY5 binds to the miR858a promoter to regulate its expression‎. Overexpression‎ of miR858a partially complements the long hypocotyl phenotype of the hy5 mutant and rescues the anthocyanin levels in the mutant. Additionally, overexpression‎ of miR858a in wild-type Arabidopsis significantly induces expression‎ anthocyanin pathway genes, such as DFR, ANS, TT8, GL3, and increases anthocyanin accumulation68. miR858a and HY5 regulate the activity of MYBL2, a negative regulator of anthocyanin, by translational inhibition and chromatin modification. Overall, multiple regulatory mechanisms involving miRNA858a and HY5 regulate the light-induced anthocyanin accumulation in Arabidopsis. In apple, light induces anthocyanin accumulation but reduces lignin level. A recent study has demonstrated that the inverse correlation between anthocyanin and lignin accumulation is mediated by the light-induced miRNA712569. RNAseq and miRNAseq analyses, combined with experimental data, suggest that cinnamoyl-coenzyme A reductase gene (CCR), a key enzyme in the lignin pathway, is the target of miRNA7125. Additionally, both the activator MdMYB1 and the repressor MdMYB16 of anthocyanin biosynthesis bind to the miRNA7125 promoter to regulate its expression‎. The interplay among MdMYB1/MYB16, CCR, and miRNA7125 maintains the homeostasis between anthocyanin and lignin in response to light69. In red Chinese sand pear (Pyrus spp.), light-induced anthocyanin accumulation is regulated by the PyPIF5-PymiR156a-PySPL9-PyMYB114/MYB10 module. PyMYB114 and PyMYB10 are components of the MBW complex that positively regulates anthocyanin biosynthesis. In contrast, pySPL9 and PyPIF5 negatively regulate anthocyanin biosynthesis. PySPL9 is a target of PymiR156, and it interacts with PyMYB114/MYB10, inhibiting the MBW complex formation and affecting anthocyanin accumulation. PyPIF5 regulates the PymiR156 expression‎ by binding to the G-box motif in the promoter. Light induces the expression‎ of PymiR156 but reduces that of PyPIF5. The light-induced upregulation of miRNA156 results in the degradation of PySPL9, leading to higher anthocyanin accumulation. In addition, overexpression‎ of miR156 induces anthocyanin accumulation in pear fruit skin. Collectively, these studies underscore the importance of miRNAs in light-induced anthocyanin accumulation (Fig. 3a)70.

Light plays a crucial role in plant adaptation to changing environments and is perceived by photoreceptors that transduce different wavelengths of light into physiological responses through intracellular signaling pathways71. The protein kinases (PKs) are major components of various signaling pathways including light. PKs regulate many biological processes in plants, including growth and development, phytohormone signaling, and responses to abiotic and biotic factors. PKs are activated in response to various signals and phosphorylate diverse substrates, including TFs and enzymatic proteins, to induce appropriate responses. In Arabidopsis, PAP1 is a component of the MBW complex that positively regulates anthocyanin biosynthesis. The mitogen-activated protein kinase 4 (MAPK4) interacts with PAP1 to increase its stability, which is essential for anthocyanin accumulation in response to light72. In apple, MPK4 has been reported to mediate the phosphorylation of MYB1 to enhance light-induced anthocyanin accumulation73. Analysis of apple fruit phosphoproteome in response to light identified HY5 to be differentially phosphorylated. Protein-protein interaction and phosphorylation assays revealed that MPK6 phosphorylates HY5 and its activity is increased by light, which is crucial for increased anthocyanin accumulation74. Apart from MPKs, other groups of kinases also regulate anthocyanin biosynthesis. In Arabidopsis, the Sucrose non-fermenting Related Kinase 1 (SnRK1) represses anthocyanin biosynthesis at both transcriptional and post-translational levels. SnRK1 inhibits the expression‎ of PAP1, triggering the dissociation of the MBW complex and the degradation of PAP1 (Fig. 3b)75.

In Arabidopsis, anthocyanin accumulation is induced by light and suppressed in the dark. COP1 and SPA are components of the E3 ubiquitin ligase complex, and are involved in the dark suppression of anthocyanin accumulation. E3 ubiquitin ligases are components of the 26 S proteasomal degradation machinery. The cop1 mutant accumulates anthocyanin in the dark when a functional PAP1 is present. Protein-protein interaction studies indicated that PAP1 and PAP2 interact with COP1 and SPA1, and PAP1 and PAP2 proteins are degraded in the dark but stable under light. In addition, PAP2 degradation is dependent on the 26 S proteasome and COP176. Similarly, in apple, MdMYB1, a homolog of PAP1 and positive regulator of anthocyanin, is accumulated under light but degraded in the dark. MdCOPs interact with MdMYB1 and are necessary for the MYB1 degradation in the dark77.

Regulation of stilbene biosynthesis by light

Stilbenes, particularly trans-Resveratrol (t-Res), are phenolic compounds found in various plant species such as grapes (Vitis vinifera). t-Res has gained significant attention due to its roles in plant defense mechanisms and its potential health-promoting properties. Stilbenes are derived from the general phenylpropanoid pathway, and stilbene synthase (STS) catalyzes the conversion of three units of malonyl-CoA and one unit of p-coumaroyl CoA into t-Res in a single step. Res accumulation is induced by UV light (UV-B and UV-C). UV-C is more effective than UV-B in inducing stilbenes, including Res, in grapes. The regulation of Res in response to UV has been extensively studied in grape vines. R2R3 MYB (VvMYB14 and VvMYB30) and WRKY (WRKY8) TFs are involved in the regulation of Res biosynthesis in response to UV irradiation. VvMYB14 and WRKY8 are activators, whereas MYB30 is a repressor of Res biosynthesis. UV-B and UV-C irradiation induce the expression‎ of the grape STS15/21, VvMYB14, and VvWRKY8 genes, but repress VvMYB30, suggesting that an activator-repressor module controls the accumulation of Res in response to UV78.

빛에 의한 스틸벤 생합성 조절

스틸벤,

특히 트랜스레스베라트롤(t-Res)은

포도(포도나무)와 같은 다양한 식물 종에서 발견되는 페놀 화합물로,

식물 방어 메커니즘에서의 역할과 잠재적인 건강 증진 특성으로 인해 큰 주목을 받고 있습니다.

스틸벤은

일반적인 페닐프로파노이드 경로에서 파생되며,

스틸벤 신타제(STS)는 세 단위의 말로닐-CoA와 한 단위의 p-쿠마로일 CoA를 한 번에 t-Res로 전환하는 촉매 작용을 합니다.

Res 축적은 자외선(UV-B 및 UV-C)에 의해 유도됩니다. UV-C는 포도의 Res를 포함한 스틸벤을 유도하는 데 UV-B보다 더 효과적입니다. 자외선에 대한 Res의 조절은 포도 포도나무에서 광범위하게 연구되었습니다. R2R3 MYB(VvMYB14 및 VvMYB30) 및 WRKY(WRKY8) TF는 자외선 조사에 따른 Res 생합성 조절에 관여합니다. VvMYB14와 WRKY8은 활성화제인 반면, MYB30은 Res 생합성을 억제합니다. UV-B와 UV-C 조사는 포도 STS15/21, VvMYB14 및 VvWRKY8 유전자의 발현을 유도하지만 VvMYB30을 억제하여 활성화자-억제자 모듈이 UV78에 반응하여 Res의 축적을 제어한다는 것을 시사합니다.

Regulation of carotenoid and artemisinin biosynthesis by light

Terpenoids are synthesized from the five-carbon precursors isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP)79. They are classified based on the number of five-carbon units in their skeletons, ranging from hemi- (C5) to tetra- (C40) terpenoids. Terpene synthase (TPS) is the key enzyme responsible for synthesizing the basic backbone structures. In nature, terpenoids serve various biological functions80, for instance, carotenoids function as photosynthetic pigments, while certain terpenoids emit volatile floral scents to attract the pollinators. Many terpenoids are defense molecules against pathogens. In addition, various terpenoids possess therapeutic properties and have been used in the treatment of various diseases. For example, artemisinin, produced by Artemisia annua (sweet wormwood), is a well-known effective antimalarial drug. Light plays a crucial role in regulating biosynthesis and accumulation of terpenoids in many plant species81,82,83,84.

Here, we highlight the roles of light on in regulation of the biosynthesis of two terpenoids, carotenoids and artemisinin.

Carotenoids are tetra-terpenoids widely distributed in plants and are responsible for the red, orange, or yellow colors observed in flowers, fruits, and roots85 (Fig. 1). In addition to their roles in pigmentation, carotenoids serve as essential photosynthetic pigments in chloroplasts. The primary function of carotenoid is to protect the photosynthetic apparatus from photooxidative damage caused by excessive illumination85,86. The biosynthesis of carotenoids is intricately regulated by light and is closely associated with the development of chloroplasts87,88. Carotenoids biosynthesis starts with the formation of phytoene, which is produced from two molecules of geranylgeranyl pyrophosphate (GGPP) catalyzed by phytoene synthase (PSY)85. Phytoene undergoes a series of enzymatic steps, including desaturation, cyclization, and hydroxylation, resulting in the production of carotenoids with a wide range of colors (Fig. 4). Among the biosynthetic enzymes involved in carotenoid biosynthesis, PSY is considered a rate-limiting enzyme and its gene expression‎ is regulated by light. Recent evidence suggests that the major light signaling factors, including PIFs, HY5, BBXs, COP1, and DET1, regulate the expression‎ of genes involved in carotenoid biosynthesis and accumulation88. PIFs play a negative regulatory role in carotenoid biosynthesis by repressing the expression‎ of PSY. The PIF-PSY regulatory module has been observed in many plant species, including Arabidopsis89, tomato90, and grape berry91. PIFs directly repress PSY in Arabidopsis and tomato fruit. In contrast, HY5 positively regulates carotenoid biosynthesis in both Arabidopsis12 and tomato92,93.

In tomato fruit, HY5 directly regulates multiple carotenoid biosynthetic genes, including PSY, Z-ISO (15-cis-zeta-carotene isomerase), CrtISO1 (carotene isomerase 1), LCYB (lycopene beta-cyclase), LCYE (lycopene epsilon-cyclase), and VDE (violaxanthin de-epoxidase), indicating a broader regulatory role for HY5 on the carotenoid pathway compared to PIFs. Both PIF1 and HY5 directly bind to the G-box in the PSY promoter in Arabidopsis, and these two proteins exhibit antagonistic effects on PSY expression‎, highlighting their opposing roles in carotenoid biosynthesis12. BBX proteins have also been implicated as regulators of carotenoid biosynthesis in tomato19 and pepper94. However, their regulatory roles appear to be limited to specific carotenoid biosynthetic genes, such as PSY in tomato and CCS (capsanthin-capsorubin synthase) in pepper. Silencing of COP1 or DET1 significantly enhanced the accumulation of carotenoids in tomato92,95, suggesting the negative roles of both light-regulated E3 ubiquitin ligases in carotenoid metabolism (Fig. 4a).

빛에 의한 카로티노이드 및 아르테미시닌 생합성 조절

테르페노이드는

5탄소 전구체인 이소펜테닐 파이로인산염(IPP)과 디메틸알릴 파이로인산염(DMAPP)79 으로부터 합성됩니다.

테르페노이드는

골격에 포함된 5탄소 단위의 수에 따라

헤미(C5)에서 테트라(C40) 테르페노이드까지 분류됩니다.

테르펜 신타제(TPS)는

기본 골격 구조를 합성하는 핵심 효소입니다.

자연에서 테르페노이드는

다양한 생물학적 기능을 수행합니다80

예를 들어

카로티노이드는

광합성 색소 역할을 하고,

특정 테르페노이드는 휘발성 꽃 향기를 발산하여

수분 매개체를 유인합니다.

많은 테르페노이드는

병원균에 대한 방어 분자입니다.

또한

다양한 테르페노이드는 치료 특성을 가지고 있으며

다양한 질병 치료에 사용되어 왔습니다.

예를 들어,

아르테미시닌은

개똥쑥에서 생성되며 효과적인 항말라리아제로 잘 알려져 있습니다.

빛은

많은 식물 종에서

테르페노이드의 생합성과 축적을 조절하는 데

중요한 역할을 합니다81 ,82,83,84.

여기에서는

두 가지 테르페노이드인

카로티노이드와 아르테미시닌의 생합성 조절에서

빛의 역할에 대해 중점적으로 살펴봅니다.

카로티노이드는

식물에 널리 분포하는 테트라 테르페노이드이며

꽃, 과일, 뿌리에서 관찰되는 빨간색, 주황색 또는 노란색을 담당합니다85 (그림 1).

카로티노이드는

색소 침착에 대한 역할 외에도

엽록체에서 필수적인 광합성 색소 역할을 합니다.

카로티노이드의 주요 기능은

과도한 조명으로 인한 광산화 손상으로부터

광합성 장치를 보호하는 것입니다85 ,86.

카로티노이드의 생합성은

빛에 의해 복잡하게 조절되며

엽록체의 발달과 밀접한 관련이 있습니다87,88.

카로티노이드 생합성은

피토엔 합성 효소(PSY)에 의해 촉매되는

두 분자의 제라닐게라닐 파이로인산(GGPP)으로부터 생성되는

피토엔의 형성으로시작됩니다85.

피토엔은

불포화, 고리화, 히드록실화 등 일련의 효소 단계를 거쳐

다양한 색상의 카로티노이드를 생성합니다(그림 4).

카로티노이드 생합성에 관여하는 생합성 효소 중 PSY는

속도 제한 효소로 간주되며,

그 유전자 발현은 빛에 의해 조절됩니다.

최근의 증거에 따르면

PIF, HY5, BBX, COP1 및 DET1을 포함한 주요 빛 신호 인자가

카로티노이드 생합성 및 축적에 관여하는 유전자의 발현을 조절하는 것으로 나타났습니다88.

PIF는

PSY 의 발현을 억제하여 카로티노이드 생합성에서

부정적인 조절 역할을 합니다.

아라비돕시스89, 토마토90, 그레이프 베리91 등

많은 식물 종에서 PIF-PSY 조절 모듈이 관찰되었습니다.

PIF는

애기장대와 토마토 열매에서 PSY를 직접적으로 억제합니다.

반면, HY5는 애기장대12와 토마토92,93 모두에서 카로티노이드 생합성을 긍정적으로 조절합니다.

토마토 열매에서

HY5는 PSY, Z-ISO (15-cis-zeta-carotene isomerase),

CrtISO1 (카로틴 이소머라제 1),

LCYB (리코펜 베타-사이클레이스),

LCYE (리코펜 엡실론-사이클레이스),

VDE (비락산틴 디에폭시다제) 등

여러 카로티노이드 생합성 유전자를 직접 조절하여

PIF에 비해 HY5의 조절 역할이 더 넓다는 것을 나타냅니다.

PIF1과 HY5는

모두 애기장대에서 PSY 프로모터의 G-박스에 직접 결합하며,

이 두 단백질은 카로티노이드 생합성에서 상반된 역할을 강조하면서 PSY 발현에 길항 효과를 나타냅니다12 .

BBX 단백질은

토마토19 와 고추94 에서도 카로티노이드 생합성의 조절자로서 관련되어 있습니다.

그러나 이들의 조절 역할은 토마토의 PSY와 고추의 CCS (캡산틴-캡소루빈 합성 효소)와 같은 특정 카로티노이드 생합성 유전자에 국한된 것으로 보입니다. COP1 또는 DET1의 침묵은 토마토에서 카로티노이드의 축적을 크게 향상시켰습니다92,95, 이는 카로티노이드 대사에서 두 빛 조절 E3 유비퀴틴 리가제의 부정적인 역할을 시사합니다(그림 4a).

Fig. 4: Light regulation of carotenoid and artemisinin biosynthesis.

a Left panel, schematic diagram of the carotenoid biosynthetic pathway in pants. The light-responsive genes encoding carotenoid biosynthetic pathway enzymes are highlighted red. PSY phytoene synthase, PDS phytoene desaturase, Z-ISO ζ-carotene isomerase, ZDS ζ-carotene desaturase, CrtISO carotenoid isomerase, LCYB lycopene β-cyclase, LCYE lycopene ε-cyclase, CYP97A cytochrome P450 β-carotene hydroxylase, CYP97C cytochrome P450 ε-carotene hydroxylase, BCH β-carotene hydrolase, ZEP zeaxanthin epoxidase, VDE violaxanthin de-epoxidase, NXS neoxanthin synthase. Right panel, carotenoid biosynthesis is induced by light through the activators HY5, BBX20, bHLH1/2, and NAC22, as well as the repressors COP1, DET1, and PIF1. Light enhances carotenoid production by simultaneously inducing transcriptional activators bHLH1/2 and NAC22 while suppressing negative regulators COP1, DET1, and PIF1. HY5 and PIF1 inhibit each other and compete to regulate the carotenoid biosynthetic genes. Light suppresses DET1, which is a negative regulator of BBX20 and HY5. b Left panel, schematic diagram of the artemisinin biosynthetic pathway in Artemisia annua. The light-responsive genes encoding artemisinin biosynthetic pathway enzymes are highlighted in red. ADS amorpha-4,11-diene synthase, CYP71AV1 amorpha-4,11-diene hydroxylase (cytochrome P450 monooxygenase), CPR cytochrome P450 reductase, ALDH1 aldehyde dehydrogenase 1, DBR2 artemisinic aldehyde Δ11(13) reductase, GST glandular secretory trichome. Right panel, artemisinin biosynthesis is induced by light through the activators AaHY5, AaMYB108, three WRKYs, and AaORA, as well as the repressors AaCOP1 and AaMYB15. AaHY5 and AaMYB108 act upstream of the WRKYs and AaORA to regulate their activities. AaHY5 and AaMYB108 are targeted by AaCOP1 for degradation in the dark. The expression‎ of AaMYB15, a repressor of artemisinin biosynthesis, is repressed by light. Solid and dotted arrows indicate direct and indirect regulation, respectively. AaORA Artemisia annua OCTADECANOID-DERIVATIVE RESPONSIVE AP2-DOMAIN PROTEIN, AaGSW1 GLADULAR TRICHOME SPECIFIC WRKY1. Solid and dotted T-bars indicate direct and indirect repression, respectively.

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The regulation of carotenoids in response to light involves not only the core light signaling regulators, but also other TFs that play important roles in various plant species. In papaya (Carica papaya), two bHLH TFs, CpbHLH1 and CpbHLH2, are induced by light during fruit ripening and activate carotenoid biosynthetic genes96. Similarly, during kumquat (Fortunella crassifolia) fruit ripening, a NAC (NAM/ATAF/CUC2) family TF gene, FcrNAC22, is upregulated by light, triggering the expression‎ of carotenoids pathway genes97. However, the relationships of these bHLH and NAC TFs with the core light signaling components need further investigation and verification.

Artemisinin is an oxygenated sesquiterpene synthesized and stored in the glandular secretory trichomes (GSTs) of A. annua leaves98 (Fig. 1). The precursor of artemisinin, amorpha-4,11-diene, is formed by the cyclization of farnesyl diphosphate (FPP). Subsequently, amorpha-4,11-diene is converted to artemisinin through several enzymatic steps and non-enzymatic reactions (Fig. 4). Light induces artemisinin accumulation through upregulating key pathway genes, such as CYP71AV1 and AaDBR2 (artemisinic aldehyde Δ11(13) reductase). The biosynthesis of artemisinin is positively regulated by AaHY599. AaHY5 directly induces the expression‎ of three WRKY TFs, AaGSW1 (Glandular trichome specific WRKY1)99, AaWRKY9100 and AaWRKY14101. These WRKY TFs, in turn, activate genes encoding key enzymes in the artemisinin biosynthetic pathway. AaGSW1 and AaWRKY14 directly target CYP71AV198,101 while AaWRKY9 directly activates AaDBR2 and AaGSW1100. In addition, AaGSW1 indirectly induces artemisinin pathway enzymes through activating the expression‎ AaORA (octadecanoid-derivative responsive AP2-domain protein)98, another transcriptional activator of artemisinin biosynthesis102. A recent study has shown that AaGSW1 interacts with the R2R3 MYB TF AaMYB108 to induce the expression‎ of CYP71AV1, which encodes a cytochrome P450 monooxygenase in the artemisinin pathway103. Moreover, both AaHY5 and AaMYB108 are targets of AaCOP1103, further highlighting the complexity of the transcriptional regulatory network controlling artemisinin biosynthesis in response to light (Fig. 4b).

The development of GSTs in A. annua leaves is crucial for the accumulation of artemisinin. Recent research has shed light on the regulatory mechanisms governing GST development and initiation, particularly involving the AaCOP1 protein104. In the darkness, AaCOP1 interacts with and facilitates the degradation of AaSEP1, a positive regulator of GST initiation. The AaSEP1-AaMYB16-AaHD1 regulatory complex regulates GST initiation104,105. AaHD1 directly activates the expression‎ of AaGSW2, an activator of GST initiation106. AaMYB16 enhances the activation of AaHD1 on the AaGSW2 promoter through their interaction, and the interaction between AaSEP1 and AaMYB16 further strengthens this activation process. AaCOP1 not only regulates the protein level of AaSEP1 but also influences the transcript level of AaSEP1 in response to light. The specific mechanism through which light induces the transcription of AaSEP1 remains unknown104.

Regulation of the biosynthesis of alkaloids and nitrogen-containing metabolites by light

Alkaloids, which are nitrogen-containing compounds, have been studied extensively for their functions in plant defense against pathogens and insects. Different types of alkaloids and nitrogen-containing metabolites, such as terpenoid indole alkaloids (TIA) in Catharanthus roseus (Madagascar periwinkle)107, steroidal glycoalkaloids (SGA) in Solanum lycopersicum (tomato)108,109,110, and glucosinolates (GSL) in Arabidopsis111, have been the focus of research for their roles in plant defense and benefits in human health. While the biosynthesis and regulation of these SM by the phytohormone jasmonate acid (JA) have been a major focus of many studies112, recent research has highlighted the regulatory roles of light in the biosynthesis of GSLs113, alkaloids including vindoline in C. roseus114, camptothecin in Camptotheca acuminata (Chinese Happy Tree)115, and SGAs in tomato (Fig. 1)116.

C. roseus is the source of more than 130 TIAs including the anticancer drugs vincristine and vinblastine117. TIA biosynthesis is a highly complex process involving more than 30 enzymes and 20 regulatory proteins. The biosynthesis of TIAs starts with the condensation of tryptamine, derived from the indole branch of the pathway, and secologanin, derived from the iridoid branch, to form strictosidine, which is the universal precursor for all TIAs, including ajmalicine, serpentine, tabersonine, catharanthine, and vindoline (Fig. 5)118,119. Vincristine and vinblastine are derived from the condensation of vindoline and catharanthine. Vindoline is preferentially accumulated in the aerial parts of the plant and is induced by light in a phytochrome-dependent manner120. The biosynthesis of vindoline from tabersonine involves seven enzymatic steps121, and the expression‎ of five of the seven genes, including T16H2 (tabersonine 16-hydroxylase), T3O (tabersonine 3- oxidase), T3R (tabersonine 3-reductase), D4H (desacetoxyvindoline-4-hydroxylase), and DAT (deacetylvindoline 4-Oacetyltransferase) is induced by light114. A recent study has revealed that the core components of the light signaling influence vindoline biosynthesis in C. roseus. CrPIF1 is a negative regulator of vindoline biosynthesis while the GATA-type zinc finger family TF, CrGATA1, acts as a positive regulator114. Specifically, CrPIF1 represses the expression‎ of CrGATA1, T16H2, and DAT, whereas CrGATA1 activates the expression‎ of the five vindoline biosynthetic genes that are responsive to light114. It has been suggested that the CrPIF1 suppresses vindoline biosynthesis in the dark, and the degradation of CrPIF1 upon exposure to light triggers the induction of vindoline biosynthesis by CrGATA1 (Fig. 5a)114.

빛에 의한 알칼로이드 및 질소 함유 대사산물의 생합성 조절

질소 함유 화합물인 알칼로이드는 병원균과 곤충에 대한 식물 방어 기능에 대해 광범위하게 연구되어 왔습니다. 카타란투스 로제우스 (마다가스카르 대수리)107 의 테르페노이드 인돌 알칼로이드(TIA), 솔라눔 리코퍼시쿰 (토마토)108,109,110 의 스테로이드 글리코알칼로이드(SGA), 애기장대111 의 글루코시놀레이트(GSL) 등 다양한 유형의 알칼로이드와 질소 함유 대사산물이 식물 방어에 미치는 역할과 인체 건강에 미치는 효능에 대해 연구되어 왔습니다. 식물 호르몬인 자스모네이트산(JA)에 의한 이러한 SM의 생합성과 조절은 많은 연구의 주요 초점이 되어 왔지만112, 최근 연구에서는 GSL113, C. roseus의 빈돌린을 포함한 알칼로이드114, 캠토테카 아쿠미나타 (중국 해피트리)115, 토마토(그림 1)116 의 생합성에서 빛의 조절 역할이 강조되고 있습니다 .

C. 로즈수스는 항암제 빈크리스틴과 빈블라스틴을 포함한 130여 가지 TIA의 원천입니다117. TIA 생합성은 30개 이상의 효소와 20개 이상의 조절 단백질이 관여하는 매우 복잡한 과정입니다. TIA의 생합성은 경로의 인돌 가지에서 파생된 트립타민과 이리도이드 가지에서 파생된 세콜로가닌이 응축되어 아즈말린, 세펜틴, 타버닌, 카타란틴 및 빈돌린을 포함한 모든 TIA의 보편적인 전구체인 스트릭토시딘을 형성하는 것으로 시작합니다(그림 5)118,119. 빈크리스틴과 빈블라스틴은 빈돌린과 카타란틴의 응축에서 파생됩니다. 빈돌린은 식물의 공중 부분에 우선적으로 축적되며 피토크롬 의존적인 방식으로 빛에 의해 유도됩니다120. 타버슨린에서 빈돌린의 생합성에는 7가지 효소 단계가 포함되며121, 7가지 유전자 중 5가지 유전자, 즉 T16H2 (타버슨린 16- 하이드 록실 라제) , T3O (타버슨린 3- 옥시다제) , T3R (타버슨린 3- 리덕타제), D4H (데사 세 톡시 빈돌린4- 하이드 록실 라제) 및 DAT (데아 세틸 빈돌린 4-오 아세틸 트랜스퍼 라제)의 발현은 빛114 에 의해 유도된다. 최근 연구에 따르면 빛 신호의 핵심 성분이 C. roseus 의 빈돌린 생합성에 영향을 미친다는 사실이 밝혀졌습니다. CrPIF1은 빈돌린 생합성의 음성 조절인자인 반면, GATA형 아연 핑거 계열 TF인 CrGATA1은 양성 조절인자로 작용합니다114. 구체적으로 CrPIF1은 CrGATA1, T16H2, DAT 의 발현을 억제하는 반면, CrGATA1은 빛에 반응하는 5개의 빈돌린 생합성 유전자의 발현을 활성화합니다114. CrPIF1은 어둠 속에서 빈돌린 생합성을 억제하고, 빛에 노출되면 CrPIF1의 분해가 CrGATA1에 의한 빈돌린 생합성 유도를 유발하는 것으로 제안되었습니다(그림 5a)114.

Fig. 5: Light regulation of TIA, SGA, and GSL biosynthesis.

a Left three panels, schematic diagrams of the vindoline, camptothecin, and steroidal glycoalkaloid (SGA) biosynthetic pathways in Catharanthus roseus, Camptotheca acuminata, and tomato (Solanum lycopersicum), respectively. The light-responsive genes encoding the enzymes are highlighted in red. T16H2 tabersonine 16-hydroxylase 2, 16OMT 16-O-methyl transferase, T3O tabersonine 3-oxygenase, T3R tabersonine 3-reductase, NMT N-methyltransferase, D4H desacetoxyvindoline-4-hydroxylase, DAT deacetylvindoline-4-Oacetyltransferase, G8O geraniol-8-oxidase, CYC1 CYCLASE1, 7-DLS 7-deoxyloganetic acid synthase, 7-DLGT 7-deoxyloganetic acid glucosyltransferase, 7-DLH 7-deoxyloganic acid hydroxylase, SLAS secologanic acid synthase, TDC1 tryptophan decarboxylase 1, STRAS strictosidinic acid synthase, GAME GLYCOALKALOID METABOLISM. Right panel, light-regulation of vindoline, camptothecin, and SGAs in respective plants. Light-induced TIA (vindoline) biosynthesis in Cathranthus roseus is regulated by transcription factors CrGATA1 and CrPIF1. The expression‎ of CrGATA1, an activator of vindoline biosynthesis, is induced by light. CrPIF1 suppresses CrGATA1, but it is degraded by light, thus releasing CrGATA to activate the vindoline pathway. CrPIF1 also directly represses vindoline biosynthesis. Camptothecin biosynthesis in Camptotheca acuminata is repressed by light through activation of CaLMF. In tomato, light induces SGA biosynthesis by upregulating the activator SlHY5 while suppressing the repressor SlPIF3. b Left two panels, schematic diagram of the aliphatic and indolic glucosinolates (GSL) biosynthetic pathway in Arabidopsis thaliana. The light-responsive genes encoding the enzymes are highlighted in red. Methylthioalkylmalate synthase (MAM1, MAM3), cytochrome P450 monooxygenases (CYP79B2, CYP79B3, CYP79F1, CYP79F2, CYP83A1, CYP83B1), glutathione S-transferase (GSTF9, GSTF10, GSTF11, GSTU20), γ-glutamyl peptidase (GGP1, GGP3), SUR1 SUPERROOT 1, UDP-glycosyltransferase (UGT74B1, UGT74C1), sulfotransferases (SOT16, SOT17, SOT18). Right panel, the biosynthesis of indolic and aliphatic GSL in Arabidopsis is regulated by light through the activators MYB34/51/122 and MYB28/29/76. BBX29 is a positive regulator of MYB52/34. Light inhibits COP1 which is a repressor of HY5, and the activated HY5 positively regulates MYB34/51/122, thus increasing indolic GSL biosynthesis. However, HY5 represses MYB28/29/76, thus reducing aliphatic GSL biosynthesis. CaLMF, Camptotheca acuminata Light-Mediated Camptothecin Biosynthesis Factor. Solid and dotted arrows indicate direct and indirect regulation, respectively. Solid and dotted T-bars indicate direct and indirect repression, respectively.

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Camptothecin is a TIA produced in C. acuminata and has shown antitumor activity against cancers in breast, ovarian, colon, lung, and stomach122,123. Camptothecin is accumulated in all tissues with the shoot apex and young leaf accumulating the highest levels124. In C. acuminata, camptothecin biosynthesis begins with the condensation of tryptamine and secologanic acid to produce strictosidinic acid (Fig. 5). The subsequent steps in camptothecin biosynthesis have not been fully elucidated124. Although it has been known for some time that camptothecin production is negatively regulated by light, the regulatory mechanism remained unknown125. A recent research has revealed that light suppresses camptothecin biosynthesis by affecting the expression‎ of four crucial camptothecin biosynthesis genes, CaTDC1, CaG8O, CaCYC1, and Ca7-DLS115. A bZIP TF, CaLMF (Light-Mediated camptothecin Biosynthesis Factor), has been identified as a regulator of the light-induced suppression of camptothecin biosynthesis. Light induces the expression‎ of CaLMF, which represses the expression‎ of four camptothecin biosynthetic genes (Fig. 5a)115. Although CaLMF shares significant sequence similarity with AtHY5, its functional role as a HY5-like protein requires further investigation.

Solanaceous species, such as tomato and potato, produce SGAs, which are toxic alkaloids involved in defense against biotic stress. In tomato, the major SGA is α-tomatine, which is highly accumulated in immature fruits to provide protection against pathogens and predators108. SGAs are derived from cholesterol through a series of enzymatic reactions, including hydroxylation, oxidation, transamination, and glycosylation. The enzymes catalyzing these steps are well characterized and known as GLYCOALKALOID METABOLISM enzymes (GAMEs) (Fig. 5)109,110. SGA biosynthesis is light inducible as most of the GAMEs are upregulated in response to light exposure126. The core light signaling components, including the activator SlHY5116,126 and the repressor SlPIF3126, regulate SGA biosynthesis. Specifically, SlHY5 directly activates the genes encoding GAME1, GAME4, and GAME17, while SlPIF3 acts as a repressor (Fig. 5a)126. These findings suggest that the tomato SGAs biosynthesis is tightly regulated by the core light signaling components.

GSLs are a diverse group of nitrogen and sulpfur-containing SM found in the Brassicaceae family plants including Arabidopsis111,127. GSLs play important roles in plant defense against various pests and diseases and have significant medicinal values127,128. They can be converted by intestinal bacteria into isothiocyanates, which have anti-inflammatory, anti-cancer, anti-obesity, and neuroprotective properties129. Recent research has shed light on the molecular mechanisms that govern the regulation of two major types of GSLs, aliphatic and indolic GSL, which are derived from the amino acid methionine and tryptophan, respectively (Fig. 5). The effects of light on GSL biosynthesis have been studied in many plant species113,130,131. The indolic and aliphatic GSL biosynthetic pathways can be divided into three independent stages, i.e. chain elongation of the amino acids, construction of the GSL structure, and secondary modifications of the amino acid side chain132. Light upregulates six GSL biosynthetic genes, including three involved in the biosynthesis of aliphatic GSL (CYP79F1, MAM-L, and SOT17), two in indolic GSL (CYP79B2 and SOT16), and one associated with both types of GSL (SOT18)113. The expression‎ of GSL pathway genes is regulated by a group of MYB TFs in Arabidopsis. The biosynthesis of aliphatic GSL is positively regulated by MYB28, MYB29, and MYB76, while that of indolic GSL is regulated by MYB34, MYB51, and MYB122133,134. The MYB genes associated with aliphatic GSL are induced by light and repressed in dark, while the expression‎ patterns of those associated with indolic GSL vary in response to light113. Expression‎ of MYB51 is repressed in the dark but not induced by light, whereas that of MYB34 is induced by light but not affected in the dark. MYB122 is induced in the dark but does not respond to light. Light regulation of GSL is partially dependent on HY5, which positively regulates CYP79F1, CYP79B2, and SOT18. Expression‎ of all three aliphatic GSL-associated MYB28, MYB29, and MYB76 are strongly induced by light in the hy5 mutant compared to wild-type Arabidopsis, whereas that of indolic GSL-associated MYB34 and MYB122 are repressed, suggesting that HY5 may act as a repressor of aliphatic GSL and an activator of indolic GSL. Interestingly, although the aliphatic MYBs are strongly induced in the hy5 mutant, the degree of upregulation of the pathway genes are not significant, and, therefore, the hierarchy of MYBs and HY5 still needs to be established113. In addition, the BBX family TF AtBBX29 activates GSL biosynthesis in response to light, possibly acting through MYB34 and MYB51135. COP1, the negative regulator of light signaling pathway, plays a positive role in regulating GLS biosynthesis134. In cop1 mutant lines, the reduced accumulation of both types of GSLs is consistent with downregulation of the aliphatic GSL biosynthetic gene CYP83A1 and the indolic GSL biosynthetic genes CYP79B3 and CYP83B1, as well as MYB34. However, the expression‎ of MYB51 and MYB122 is upregulated in cop1 mutant lines. In contrast to the positive regulator HY5, some activators of GSL biosynthesis are negatively regulated by light, with COP1 playing a positive role in this regulation (Fig. 5b). These findings highlight the complexity of the regulatory network governing GSL biosynthesis in response to light.

In summary, alkaloids, such as TIAs in C. roseus and SGA in tomato, are regulated by well-conserved light signaling factors such as PIFs and HY5. PIFs negatively affect the biosynthesis of TIAs and SGA. HY5 is a positive regulator of SGA in tomato, while the HY5-like factor, CaLMF, is a negative regulator of camptothecin in C. accuminata. Whether HY5 or HY5-like factors are involved in the regulation of TIAs in C. roseus remains known. The biosynthesis of aliphatic and indolic GSL is differentially regulated by HY5. Furthermore, other factors, such as MYBs and GATA-type TFs, regulate TIA and GSL biosynthesis in plants in response to light.

Conclusion and Future Perspective

The biosynthesis of SM is influenced by many environmental factors including light (Fig. 1). However, this process is energy-intensive, and excessive accumulation of certain SM can be toxic to cells. Consequently, plants have evolved intricate regulatory mechanisms to prevent overactivation and fine-tune SM biosynthesis. Accumulating evidence suggests that the regulations of most SM biosynthetic pathways are conserved across plant species. One example of such conservation is observed in the regulation of anthocyanin biosynthesis, which is controlled by the MBW complex, in a wide range of plants, including the model plant Arabidopsis. Another instance is the regulation of terpene biosynthesis, where the bHLH TF MYC2 or its orthologues govern the biosynthetic process from the eudicot Arabidopsis to the primitive land plant, Marchantia polymorpha136. Furthermore, this conserved nature extends to the biosynthesis of structurally diverse SM. For example, the biosynthesis of TIAs in C. roseus, SGA in tomato and potato, and nicotine in tobacco are regulated MYC2 and a group of phylogenetically related JA-responsive AP2/ERFs (Apetala 2/Ethylene Responsive Factors)137,138,139,140,141. The conserved nature of the regulatory mechanism is also apparent in the light signaling pathway, in which the core light signaling pathway TFs PIFs, HY5, and BBX regulate the biosynthesis of diverse groups of SM, including anthocyanins, terpenes, and TIAs in various plant species. Nonetheless, some regulatory factors seem to be species-specific, e.g., some TFs involved in anthocyanin biosynthesis are found in apples but not Arabidopsis (Fig. 2b, c), suggesting that some plant species have evolved unique responses to light. Light and JA are important regulators of many SM. However, the relationship between JA and light signaling pathways and their combined effects on the regulation of SM biosynthesis have been relatively less studied. A previous study has shown that JA-induced artemisinin biosynthesis is dependent on light. Subsequent transcriptomic analysis of JA and light-treated A. annua seedlings has identified several candidate TFs potentially involved in the regulation of artemisinin biosynthesis142. Recently, a light and JA-inducible WRKY TF, AaWRKY9 that acts downstream of AaHY5, has been identified as a positive regulator of artemisinin biosynthesis100. Similarly, AaMYB108, identified from light and JA-treated transcriptomes, is a positive regulator of artemisinin biosynthesis103. Future studies will likely identify factors involved in the light and JA-dependent regulation of other plant SM.

결론 및 향후 전망

SM의 생합성은 빛을 포함한 많은 환경적 요인의 영향을 받습니다(그림 1).

그러나 이 과정은 에너지 집약적이며 특정 SM이 과도하게 축적되면 세포에 독성을 일으킬 수 있습니다. 따라서 식물은 과도한 활성화를 방지하고 SM 생합성을 미세 조정하기 위해 복잡한 조절 메커니즘을 진화시켜 왔습니다. 축적된 증거에 따르면 대부분의 SM 생합성 경로의 조절은 식물 종에 걸쳐 보존되어 있는 것으로 나타났습니다. 이러한 보존의 한 예는 모델 식물인 애기장대를 포함한 다양한 식물에서 MBW 복합체에 의해 제어되는 안토시아닌 생합성 조절에서 관찰됩니다.

또 다른 사례는 테르펜 생합성 조절로, bHLH TF MYC2 또는 그 상동체가 외떡잎식물 애기장대에서 원시 육상 식물인 마르칸티아 폴리모파136에 이르는 생합성 과정을 관장합니다. 또한 이러한 보존 특성은 구조적으로 다양한 SM의 생합성에도 적용됩니다. 예를 들어, C. roseus의 TIA, 토마토와 감자의 SGA, 담배의 니코틴 생합성은 MYC2와 계통 발생학적으로 관련된 JA 반응성 AP2/ERF(Apetala 2/에틸렌 반응 인자)137,138,139,140,141 그룹이 조절됩니다. 조절 메커니즘의 보존된 특성은 빛 신호 경로에서도 분명하게 드러나는데, 핵심 빛 신호 경로 TF인 PIF, HY5, BBX는 다양한 식물 종에서 안토시아닌, 테르펜, TIA를 포함한 다양한 SM 그룹의 생합성을 조절합니다. 그럼에도 불구하고 일부 조절 인자는 종에 특이적인 것으로 보이는데, 예를 들어 안토시아닌 생합성에 관여하는 일부 TF는 사과에서는 발견되지만 애기장대에서는 발견되지 않아(그림 2b, c) 일부 식물 종은 빛에 대한 독특한 반응을 진화시켰음을 시사합니다. 빛과 JA는 많은 SM의 중요한 조절인자입니다. 그러나 JA와 빛 신호 경로 사이의 관계와 SM 생합성 조절에 대한 이들의 결합 효과는 상대적으로 덜 연구되었습니다. 이전 연구에 따르면 JA에 의한 아르테미시닌 생합성은 빛에 의존하는 것으로 나타났습니다. 이후 JA와 빛을 처리한 A. 안누아 묘목의 전사체 분석을 통해 아르테미시닌 생합성 조절에 잠재적으로 관여하는 여러 후보 TF를 확인했습니다142. 최근에는 AaHY5의 하류에 작용하는 빛 및 JA 유도성 WRKY TF인 AaWRKY9가 아르테미시닌 생합성의 긍정적 조절 인자로 확인되었습니다100. 마찬가지로, 광 및 JA 처리 전사체에서 확인된 AaMYB108은 아르테미시닌 생합성의 긍정적인 조절인자입니다103. 향후 연구에서는 다른 식물 SM의 빛 및 JA 의존적 조절에 관여하는 인자를 규명할 가능성이 높습니다.

While recent years have seen significant progress in understanding photo-regulation of SM biosynthesis, some existing questions are still left unanswered. Compared to transcriptional regulation, light-mediated posttranscriptional and posttranslational regulation of SM are insufficiently studied. Identification and functional characterization of additional protein kinases and miRNAs related to SM biosynthesis will further advance our knowledge on regulatory mechanisms. Follow-up questions would thus concern why such multilayered regulatory mechanisms are necessary. Phosphorylation of the MBW components by different light-responsive kinases can lead to stabilization or disassociation of the complex (Fig. 3). How then do plants balance such countereffects by kinases in response to light? In addition, many TFs are not only regulated by phosphorylation but also de-phosphorylation by protein phosphatases (PPs). The involvement of phosphatases in the photo-regulation of SM biosynthesis is currently poorly investigated. Furthermore, literature on other posttranslational modifications, such as SUMOylation, related to photo-regulation of SM biosynthesis is limited.

Phosphorylation-dephosphorylation by PKs and PPs, respectively, is an ancient regulatory mechanism that influences many biological processes in plants and animals143. Although several PKs that phosphorylate PIFs have been identified, related information on PP is limited 3,144. HY5 is shown to be phosphorylated by SPA kinases145. The regulatory roles of these PKs and PPs have been studied in respect to plant growth development144,146; however, it remains to be explored whether the PKs and PPs are involved in light-regulated SM biosynthesis.

SUMOylation is the reversible conjugation of small ubiquitin-related modifier (SUMO) peptides to the target protein and has emerged as an important posttranslational regulation mechanism in plants and animals147. SUMOylation has been implicated in many biological processes such as growth, development, biotic and abiotic stress, as well as phytohormone signaling and flowering. In Arabidopsis, SUMOylation regulates the stability of the bHLH TF ICE1 (Inducer of CBF Expression‎) by blocking its degradation which is required for activating freezing tolerance148. The bHLH TF MYC2 is crucial for Arabidopsis seedling development in blue light. Blue light induces the MYC2 SUMOylation, which is essential for MYC2 to function under blue light. SUMOylation increases the MYC2 stability and enhances its DNA binding ability. As MYC2 is also a key component of JA signaling and a regulator of many JA-responsive SM biosynthesis, future studies should include the investigation of crosstalk between light signaling and hormones, as well as SUMOylation with regard to SM biosynthesis149. In Arabidopsis, SUMOylation by the SUMO E3 ligase SIZ1 (SAP and MIZ1 domain containing ligase 1) increases PAP1 stability and is required for light-mediated anthocyanin accumulation150. It is reasonable to expect light-activated SUMOylation also affects other regulatory proteins; however, experimental verifications will be necessary.

최근 몇 년 동안 SM 생합성의 광 조절을 이해하는 데 상당한 진전이 있었지만, 일부 기존 질문은 여전히 해결되지 않은 채로 남아 있습니다. 전사 조절에 비해 SM의 빛 매개 전사 후 및 번역 후 조절은 충분히 연구되지 않았습니다. SM 생합성과 관련된 추가적인 단백질 키나아제 및 miRNA의 확인과 기능적 특성화는 조절 메커니즘에 대한 우리의 지식을 더욱 발전시킬 것입니다. 따라서 이러한 다층적 조절 메커니즘이 왜 필요한지에 대한 후속 질문이 제기될 것입니다. 서로 다른 빛 반응성 키나제에 의한 MBW 구성 요소의 인산화는 복합체의 안정화 또는 해체로 이어질 수 있습니다(그림 3). 그렇다면 식물은 빛에 반응하여 키나아제에 의한 이러한 역효과를 어떻게 균형을 맞출까요? 또한 많은 TF는 인산화뿐만 아니라 단백질 인산화효소(PP)에 의한 탈인산화에 의해서도 조절됩니다. SM 생합성의 광 조절에 포스파타제가 관여하는지는 현재 제대로 규명되지 않았습니다. 또한 SM 생합성의 광 조절과 관련된 수모일화와 같은 다른 번역 후 변형에 대한 문헌도 제한적입니다.

PK와 PP에 의한 인산화-탈인산화는 각각 식물과 동물의 많은 생물학적 과정에 영향을 미치는 오래된 조절 메커니즘입니다143. PIF를 인산화하는 여러 PK가 확인되었지만, PP에 대한 관련 정보는 제한적입니다3,144. HY5는 SPA 키나아제에 의해 인산화되는 것으로 나타났습니다145 . 이러한 PK와 PP의 조절 역할은 식물 성장 발달과 관련하여 연구되어 왔지만144,146; 그러나 PK와 PP가 빛 조절 SM 생합성에 관여하는지 여부는 아직 밝혀지지 않았습니다.

수모일화는 작은 유비퀴틴 관련 조절인자(SUMO) 펩타이드가 표적 단백질에 가역적으로 접합되는 것으로, 식물과 동물에서 중요한 번역 후 조절 메커니즘으로 부상했습니다147. 수모화는 성장, 발달, 생물학적 및 비생물학적 스트레스, 식물호르몬 신호 및 개화와 같은 많은 생물학적 과정에 관여합니다. 애기장대에서 SUMO일화는 내한성을 활성화하는 데 필요한 bHLH TF ICE1(CBF 발현 유도 인자)의 분해를 차단하여 안정성을 조절합니다148. bHLH TF MYC2는 청색광에서 애기장대 모종 발달에 중요한 역할을 합니다. 청색광은 MYC2가 청색광 아래에서 기능하는 데 필수적인 MYC2 수모일화(SUMOylation)를 유도합니다. 수모일화는 MYC2의 안정성을 높이고 DNA 결합 능력을 향상시킵니다. MYC2는 또한 JA 신호의 핵심 구성 요소이자 많은 JA 반응성 SM 생합성의 조절자이므로, 향후 연구에서는 빛 신호와 호르몬 간의 누화뿐만 아니라 SM 생합성과 관련된 SUMO일화149 에 대한 조사도 포함되어야 합니다. 애기장대에서 SUMO E3 리가제 SIZ1(SAP 및 MIZ1 도메인 함유 리가제 1)에 의한 SUMO일화는 PAP1 안정성을 증가시키고 빛을 매개로 한 안토시아닌 축적에 필요합니다150 . 빛에 의해 활성화된 수모일화는 다른 조절 단백질에도 영향을 미칠 것으로 예상되지만, 실험적 검증이 필요합니다.

Light affects the expression‎ of approximately 20 percent of genes in the Arabidopsis and rice genomes151. The massive change in the transcriptomic landscape indicates that this process is modulated at chromatin level152. Plant epigenome is indeed dynamic, and extensive research reveals the effects of light-induced epigenetic changes, such as histone methylation, histone acetylation/deacetylation, and incorporation of histone variants, on plant growth and development. The core components of the light signaling pathway, such as HY5 and PIFs, interact with and recruit epigenetic factors to regulate gene expression‎153. In addition to epigenome, epitranscriptome (posttranscriptional modification of RNA such as methylation) is considered as a part of the epigenetic system and affects many aspects of plant development153,154. However, information is limited regarding the light and epigenetic regulation of SM biosynthesis in plants. In Arabidopsis, MYBD overexpression‎ affects the acetylation status of the MYBL2 promoter and represses MYBL2 expression‎ to promote anthocyanin accumulation40. Light-induced epigenetic changes affecting the biosynthesis of other SM, and the chromatin factors involved in this process remain to be characterized. The advances in omics technology will offer promising information on epigenetic regulation of SM biosynthesis. Recently, scATACseq (single-cell Assay for Transposase-Accessible Chromatin by sequencing) has emerged as a powerful technique to study epigenomic landscape of plants at a single-cell resolution in response to biotic or abiotic factors. Single-cell RNAseq has provided valuable insights into the spatial organization and the identification of new transporters in C. roseus TIA pathway119,155. A well-assembled and annotated genome is fundamental to the success of these approaches. Although challenging, integrating scATACseq and scRNAseq in response to light or other factors will yield significant information on the regulation of SM pathways in plants.

빛은 애기장대와 벼 게놈에서 약 20%의 유전자 발현에 영향을 미칩니다151. 전사체 환경의 대규모 변화는 이 과정이 염색질 수준에서 조절된다는 것을 나타냅니다152. 식물 후성유전체는 실제로 역동적이며, 광범위한 연구를 통해 히스톤 메틸화, 히스톤 아세틸화/탈아세틸화, 히스톤 변이체의 통합과 같은 빛에 의한 후성유전학적 변화가 식물 성장과 발달에 미치는 영향이 밝혀졌습니다. 빛 신호 경로의 핵심 구성 요소인 HY5 및 PIF는 후성 유전 인자와 상호 작용하고 모집하여 유전자 발현을 조절합니다153. 후성 유전체 외에도 후성 전사체(메틸화와 같은 RNA의 전사 후 변형)는 후성 유전 시스템의 일부로 간주되며 식물 발달의 여러 측면에 영향을 미칩니다153 ,154. 그러나 식물의 SM 생합성에 대한 빛과 후성유전학적 조절에 관한 정보는 제한적입니다. 애기장대에서 MYBD 과발현은 MYBL2 프로모터의 아세틸화 상태에 영향을 미치고 MYBL2 발현을 억제하여 안토시아닌 축적을 촉진합니다40.

빛에 의한 후성유전학적 변화는 다른 SM의 생합성에 영향을 미치며, 이 과정에 관여하는 염색질 인자는 아직 규명되지 않은 상태입니다. 오믹스 기술의 발전은 SM 생합성의 후성유전학적 조절에 대한 유망한 정보를 제공할 것입니다. 최근에는 단일세포 염기서열 분석법(scATACseq)이 생물학적 또는 비생물학적 요인에 반응하여 단일세포 해상도로 식물의 후성유전체 환경을 연구하는 강력한 기술로 부상하고 있습니다. 단일 세포 RNAseq은 C. roseus TIA 경로의 공간 조직과 새로운 수송체 식별에 대한 귀중한 통찰력을 제공했습니다119,155. 이러한 접근법의 성공을 위해서는 잘 조립되고 주석이 달린 게놈이 기본입니다. 어렵지만, 빛이나 다른 요인에 반응하여 scATACseq과 scRNAseq을 통합하면 식물의 SM 경로 조절에 대한 중요한 정보를 얻을 수 있습니다.

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