식물독소 phytoalexin 탐구...

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Molecules

. 2014 Nov 5;19(11):18033–18056. doi: 10.3390/molecules191118033

Deciphering the Role of Phytoalexins in Plant-Microorganism Interactions and Human Health

Philippe Jeandet 1,*, Claire Hébrard 1, Marie-Alice Deville 2, Sylvain Cordelier 1, Stéphan Dorey 1, Aziz Aziz 1, Jérôme Crouzet 1

Editor: Derek J McPhee

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PMCID: PMC6271817  PMID: 25379642

Abstract

Phytoalexins are low molecular weight antimicrobial compounds that are produced by plants as a response to biotic and abiotic stresses. As such they take part in an intricate defense system which enables plants to control invading microorganisms. In this review we present the key features of this diverse group of molecules, namely their chemical structures, biosynthesis, regulatory mechanisms, biological activities, metabolism and molecular engineering.

초록

식물 알렉신(phytoalexins)은

생물학적 스트레스와 비생물학적 스트레스에 대한 반응으로

식물이 생산하는 저분자량 항균 화합물입니다.

low molecular weight antimicrobial compounds

따라서

식물이 침입하는 미생물을 제어할 수 있도록 하는

복잡한 방어 시스템에 참여합니다.

이 리뷰에서는

이 다양한 분자 그룹의 주요 특징, 즉

화학 구조,

생합성,

조절 메커니즘,

생물학적 활동, 대사 및 분자 공학을 소개합니다.

Keywords: phytoalexins, plants, defense mechanisms, microorganisms, biological activity

1. Phytoalexins: A Global Survey

Phytoalexins take part in an intricate defense system used by plants against pests and pathogens [1,2]. These are low molecular weight antimicrobial compounds both synthesized by and accumulated in plants as a response to biotic and abiotic stresses. The concept of phytoalexins was first introduced over 70 years ago by Müller and Börger [3] after observing that infection of potato tubers with a strain of Phytophthora infestans capable of initiating hypersensitive reactions, significantly inhibited the effect of a subsequent infection with another strain of P. infestans. This inhibition was linked to a “principle” produced by the plant cells reacting hypersensitively that they named phytoalexin [4].

Most of what is known about phytoalexins derives from extensive work on a limited number of plant families: Leguminosae or Fabaceae and Solanaceae [5,6], on one hand, and investigations on one or a few species within other plant families, namely Amaryllidaceae, Euphorbiaceae, Orchidaceae, Chenopodiaceae, Compositae, Convolvulaceae, Ginkgoaceae, Poaceae, Linaceae, Moraceae, Orchidaceae, Piperaceae, Rosaceae, Rutaceae and Umbelliferae on the other hand [7]. More intensive studies recently focused on phytoalexins from plant families of significant economic importance: Poaceae (maize and rice) [8], Vitaceae [9,10] and Malvaceae (cotton) [11]. Camalexin, the main phytoalexin from Brassicaceae (Cruciferae) has also been the subject of numerous studies focusing on its biosynthetic pathway and the regulatory networks involved in its production in the model plant Arabidopsis thaliana [1,12]. However, the question of the ubiquity of phytoalexins throughout the plant kingdom still remains.

Phytoalexins are restricted to compounds produced from remote precursors, through de novo synthesis of enzymes. This peculiarity makes deciphering their biosynthesis and regulation mechanisms very complex [1,2]. Phosphorylation cascades, defense-related marker genes, calcium sensors and elicitors as well as hormone signaling are potentially important regulators for the modulation of phytoalexin production and pathogen resistance. As a corollary, knowledge of the control mechanisms of phytoalexin accumulation has served as the basis for the genetic manipulation of those compounds in engineered plants for enhanced disease resistance [1,13,14].

The question as to whether phytoalexins are active in vivo and play a significant role in plant defense mechanisms has long been debated addressing both the actual antimicrobial activity of phytoalexins under the conditions found within plant tissues and their localization around invading organisms [15,16]. These intractable interrogations are indeed crucial to their proposed role as microbial growth regulators in infected plant tissues. Nonetheless there is considerable evidence that these compounds exhibit in vitro toxicity across much of the biological spectrum, prokaryotic and eukaryotic.

The nature of the interaction between plants and pathogens largely depends on the ability of the latter to metabolize the phytoalexins to which they are exposed. Engineering of fungal genes responsible for detoxification of phytoalexins in plants has pointed out their role in the interactions between plants and pathogens [17]. In phytopathogenic fungi, ATP-Binding Cassette (ABC) transporters may also extrude plant defense products as well as fungicides. These transporters act as virulence factors providing protection against phytoalexins produced by the host. Many factors thus interplay to affect the outcome of the interaction between plants and pathogens.

It has recently been demonstrated that phytoalexins may also display health-promoting effects in humans. For instance, resveratrol produced by Vitaceae has been acclaimed for its wondrous effects and its wide range of purported healing and preventive powers as a cardioprotective, antitumor, neuroprotective and antioxidant agent as well as an antifungal and antibacterial compound [14] (see Section 8).

1. 식물 알렉신: 글로벌 조사

식물 알렉신은

해충과 병원균에 대항하기 위해

식물이 사용하는 복잡한 방어 시스템에 관여합니다 [1,2].

이들은

생물적 및 비생물적 스트레스에 대한 반응으로

식물에 의해 합성되고

축적되는 저분자량 항균 화합물입니다.

피토알렉신이라는 개념은

70여 년 전 뮐러(Müller)와 보거(Börger)가

감자 괴경에 과민성 반응을 일으킬 수 있는 피토프토라 인페스타스(Phytophthora infestans) 균주가 감염되면

다른 피토프토라 인페스타스 균주에 의한

후속 감염의 효과가 현저하게 억제된다는 사실을 관찰한 후 처음 소개했습니다.

이 억제는

식물 세포가 과민하게 반응하여 생성된 “원리”와 관련이 있으며,

이를 식물독소(phytoalexin)라고 부릅니다 [4].

식물 알렉신에 대해 알려진 대부분의 정보는

콩과 식물(Leguminosae) 또는 콩과(Fabaceae)와 가지과(Solanaceae) [5,6] 등

제한된 수의 식물군에 대한 광범위한 연구와 다른 식물군,

즉 수선화과(Amaryllidaceae), 유향과(Euphorbiaceae), 난초과(Orchidaceae), 첸과(Chen)에 속하는

한두 종에 대한 조사에서 비롯된 것입니다.

오포디아과, 국화과, 덩굴과, 은행나무과, 벼과, 퉁퉁마디과, 뽕나무과, 난과, 깻과, 장미과, 미나리과, 

Poaceae(옥수수, 쌀) [8], Vitaceae [9,10] 및 Malvaceae(목화) [11]. 십자화과(Brassicaceae)의 주요 식물 알렉신인

카말렉신(Camalexin)은 또한 모델 식물인 애기장대(Arabidopsis thaliana)에서 생산되는 카말렉신의 생합성 경로와 관련된 조절 네트워크에 초점을 맞춘 수많은 연구의 대상이었습니다 [1,12].

그러나 식물계 전반에 걸쳐 피토알렉신이 편재하는지에 대한 의문은 여전히 남아 있습니다.

피토알렉신은

효소의 de novo 합성을 통해 원시 전구체로부터 생성되는 화합물로 제한됩니다.

이러한 특성 때문에 그들의 생합성 및 조절 메커니즘을 해독하는 것이 매우 복잡합니다 [1,2].

인산화 캐스케이드,

방어 관련 마커 유전자,

칼슘 센서 및 유도체,그리고 호르몬 신호는

식물 알렉신 생산과 병원체 저항성의 조절에

잠재적으로 중요한 조절 인자입니다.

Phosphorylation cascades,

defense-related marker genes,

calcium sensors and elicitors as well as hormone signaling

따라서,

식물 알렉신

축적의 조절 메커니즘에 대한 지식은 질병 저항성을 강화하기 위해

공학적으로 조작된 식물에서 이러한 화합물의 유전자 조작을 위한 기초가 되었습니다 [1,13,14].

식물 알렉신(phytoalexins)이

생체 내에서 활성 상태이고

식물 방어 메커니즘에서 중요한 역할을 하는지에 대한 질문은

식물 조직 내에서 발견되는 조건 하에서 식물 알렉신의 실제 항균 활성과

침입 유기체 주변의 식물 알렉신의 국소화에 관한 논의를 통해 오랫동안 논의되어 왔습니다 [15,16].

이러한 난해한 질문은

감염된 식물 조직에서

미생물 성장 조절제로서의 역할을 제안하는 데 있어 매우 중요합니다.

그럼에도 불구하고,

이러한 화합물이 원핵생물과 진핵생물 등

생물학적 스펙트럼의 대부분에 걸쳐 시험관 내 독성을 나타낸다는 상당한 증거가 있습니다.

식물과 병원균 사이의 상호 작용의 본질은

병원균이 노출된 피토알렉신(phytoalexins)을 대사하는 능력에 크게 좌우됩니다.

식물에서 피토알렉신의 해독을 담당하는 곰팡이 유전자를 조작한 결과,

식물과 병원균 사이의 상호 작용에서 그 역할이 밝혀졌습니다 [17].

식물 병원성 진균의 경우, ATP-Binding Cassette(ABC) 수송체는 살균제뿐만 아니라 식물 방어 제품도 배출할 수 있습니다. 이 수송체는 숙주에 의해 생성된 식물 방어물질에 대한 보호 기능을 제공하는 독성 인자 역할을 합니다. 따라서 식물과 병원균 간의 상호 작용 결과에 영향을 미치는 많은 요인들이 상호 작용합니다.

최근에

식물성 알렉신(phytoalexins)이

인간에게도 건강 증진 효과를 나타낼 수 있다는 사실이 입증되었습니다.

예를 들어,

포도과 식물에 의해 생성되는 레스베라트롤은

놀라운 효과와 심장 보호, 항암, 신경 보호, 항산화 작용을 하는 것으로 알려져 있으며,

항진균 및 항균 작용을 하는 화합물로도 널리 알려져 있습니다 [14] (섹션 8 참조).

Work on phytoalexins has been prolific and the production of these compounds in infected tissues has become one of the most intensively studied mechanisms of disease resistance in plants. This review will focus on some of the main features of phytoalexins:

• ○
• ○
• ○
• ○
• ○
• ○

피토알렉신에 대한 연구는 활발하게 진행되고 있으며,

감염된 조직에서 이러한 화합물이 생성되는 것은

식물 질병 저항 메커니즘에 대해 가장 집중적으로 연구된 메커니즘 중 하나가 되었습니다.

이 리뷰에서는 피토알렉신의 주요 특징 중 일부에 초점을 맞출 것입니다.

• ○화학적 다양성
• ○주요 생합성 경로 및 조절 네트워크
• ○미생물에 대한 생물학적 활성
• ○식물 질병 저항성을 위한 분자 공학
• ○곰팡이의 대사/수송
• ○인체 건강에 대한 역할

2. Chemical Diversity of Phytoalexins

Most phytoalexins produced by the Leguminosae belong to six isoflavonoid classes: isoflavones, isoflavanones, pterocarpans, pterocarpenes, isoflavans and coumestans (Table 1) ([1] and references therein). Some pterocarpan phytoalexins are especially well known: pisatin, phaseollin, glyceollin, medicarpin and maackiain. Pisatin was the first phytoalexin to be isolated and characterized from garden pea, Pisum sativum [18]. Besides these compounds, a small number of legumes also produce non-isoflavonoid phytoalexins such as furanoacetylenes and stilbenes (Table 1).

2. 피토알렉신의 화학적 다양성

콩과 식물에 의해 생성되는 대부분의 피토알렉신은

6가지 이소플라보노이드 종류에 속합니다:

이소플라본, 이소플라바논, 프테로카르판, 프테로카르펜, 이소플라반, 쿠메스탄(표 1) ([1] 및 그 안에 있는 참고문헌).

일부 피토알렉신인

피스타틴, 파세올린, 글리세올린, 메디카르핀, 마아키아인은

특히 잘 알려져 있습니다.

피스타틴은

가든피(Pisum sativum)에서 분리되고 특성화된

최초의 피토알렉신입니다[18].

이 화합물 외에도

소수의 콩과식물도 푸라노아세틸렌과 스틸벤과 같은

비이소플라보노이드 식물성 알렉신(phytoalexins)을 생산합니다(표 1).

Table 1.

Phytoalexins from different plant families.

Plant Families (in Alphabetical Order)Types of Phytoalexins/ExamplesReferences

Amaryllidaceae	Flavans	[19]
Brassicaceae (Cruciferae)	Indole phytoalexins/camalexin	[20]
	Sulfur-containing phytoalexins/brassinin	[21]
Chenopodiaceae	Flavanones/betagarin Isoflavones/betavulgarin	[22]
Compositae	Polyacetylenes/safynol	[23]
Convolvulaceae	Furanosesquiterpenes/Ipomeamarone	[24]
Euphorbiaceae	Diterpenes/casbene	[25]
Poaceae	Diterpenoids:Momilactones; Oryzalexins; Zealexins; Phytocassanes; Kauralexins	[8,26]
	Deoxyanthocyanidins/luteolinidin and apigeninidin	[26,27]
	Flavanones/sakuranetin	[1]
	Phenylamides	[28]
Leguminosae	Isoflavones Isoflavanones Isoflavans Coumestans Pterocarpans/pisatin, phaseollin, glyceollin and maiackiain Furanoacetylenes/wyerone Stilbenes/resveratrol Pterocarpens	[1] and references therein
Linaceae	Phenylpropanoids/coniferyl alcohol	[29]
Malvaceae	Terpenoids naphtaldehydes/gossypol	[11]
Moraceae	Furanopterocarpans/moracins A-H	[30]
Orchidaceae	Dihydrophenanthrenes/loroglossol	[31]
Rutaceae	Methylated phenolic compounds/xanthoxylin	[32]
Umbelliferae	Polyacetylenes/falcarinol	[33]
	Phenolics: xanthotoxin	[34]
	6-methoxymellein	[35]
Vitaceae	Stilbenes/resveratrol	[9]
Rosaceae	Biphenyls/auarperin	[36]
	Dibenzofurans/cotonefurans
Solanaceae	Phenylpropanoid related compounds	[1] and references therein
	Steroid glycoalkaloids
	Norsequi and sesquiterpenoids
	Coumarins
	Polyacetylenic derivatives

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Chen et al., describe a series of compounds produced by the genus Tephrosia, which belongs to the Leguminosae family, and possesses phytoalexin-like activities [37]. Five main classes of phytoalexins have been reported in Solanaceae: phenylpropanoid-related compounds, steroid glycolalkaloids, norsesqui- and sesquiterpenoids, coumarins and polyacetylenic derivatives (Table 1) ([1] and references therein).

Although considerable work has been done on phytoalexins from the Leguminosae and Solanaceae families, it has been recently overshadowed by the discovery of two new phytoalexin classes from the Poaceae [8,26] and Brassicaceae families [20,21]. The main phytoalexins of Poaceae (rice, maize and sorghum) are represented by members of the labdane-related diterpenoid superfamily (zealexins, kauralexins, momilactones, oryzalexins and phytocassanes) [8,26], flavanones, an unusual group of flavonoid phytoalexins, the 3-deoxyanthocyanidins [27] and phenylamides [28] (Table 1 and references therein). The current knowledge on phytoalexins produced by sorghum (3-deoxy-anthocyanidins like luteolinidin and apigeninidin) and maize (zealexins, kauralexins) has been reviewed previously [26]. Indole compounds such as camalexin and brassinin represent the major phytoalexins from the Brassicaceae family (Table 1 and references therein).

Not unexpectedly, phytoalexins from very diverse plant families are represented by many different chemical classes. Naphtaldehyde compounds such as gossypol and its derivatives constitute the main Malvaceae phytoalexins [11] (Table 1). Antifungal polyacetylenes have been isolated as phytoalexins from the Compositae and Umbelliferae families [23,33]. Furanosesquiterpenes and diterpenes constitute the phytoalexins from the Convolvulaceae and Euphorbiaceae families [24,25]. The majority of phytoalexins found in the following plant families are phenolic compounds: flavans in Amaryllidaceae [19], flavanones and isoflavones from Chenopodiaceae [22], Linaceae phenylpropanoids [29], furanopterocarpans in Moraceae [30], dihydrophenanthrenes from Orchidaceae [31], Rutaceae methylated phenolics [32], biphenyls and dibenzofurans in Rosaceae [36], xanthotoxin and 6-methoxymellein in Umbellifereae [34,35] and finally hydroxystilbenes from Vitaceae (Table 1) [1,9,10].

콩과 식물과 가지과 식물에서 식물방어물질에 대한 상당한 연구가 이루어졌지만,

최근에는 벼과 식물[8,26]과 십자화과 식물[20,21]에서

두 가지 새로운 식물방어물질이 발견되면서

그 중요성이 다소 감소했습니다.

벼과 식물(벼, 옥수수, 수수)의 주요 피토알렉신(phytoalexins)은

랩다네 관련 디테르페노이드 슈퍼패밀리(labdane-related diterpenoid superfamily)의 구성원

(제알렉신, 카우알렉신, 모밀락톤, 오리잘렉신, 피토카산)으로 대표됩니다[8,26],

플라바논, 특이한 플라보노이드 피토알렉신 그룹인

3-데옥시안토시아니딘[27] 및 페닐암 ides [28] (표 1 및 그 안의 참고 문헌).

수수(루테올리니딘과 아피제니딘 같은 3-데옥시안토시아니딘)와

옥수수(제알렉신, 카우알렉신)에서 생산되는

피토알렉신에 대한 현재의 지식은 이전에 검토된 바 있습니다 [26].

카말렉신(camalexin)과 브라시닌(brassinin)과 같은 인돌 화합물은

십자화과(Brassicaceae)의 주요 식물 알렉신(phytoalexins)을 대표합니다

(표 1 및 그 안의 참고 문헌).

예상대로, 매우 다양한 식물군의 식물 알렉신은 다양한 화학 종류로 대표됩니다.

고시폴(gossypol)과 그 유도체와 같은 나프탈데히드 화합물은

아욱과(Malvaceae)의 주요 식물 알렉신을 구성합니다[11] (표 1).

항진균성 폴리아세틸렌은

국화과와 미나리과 식물에서 식물방어물질로 분리되었습니다 [23,33].

푸라노스퀴테르펜과 디테르펜은

나팔꽃과 다래과 식물에서 식물방어물질로 구성됩니다 [24,25].

다음 식물군에서 발견되는

대부분의 피토알렉신(phytoalexins)은 페놀 화합물입니다:

수선화과의 플라반(flavan) [19], 쇠비름과의 플라바논(flavanone)과 이소플라본(isoflavone) [22], 퉁퉁마디과의 페닐프로파노이드(phenylpropanoid) [29], 모과과의 푸란오프테로카르판(furanopterocarpans) [30], 난초과의 디하이드로페난트렌(dihydrophenanthrenes) [31], 귤나무과의 메틸화 페놀(methylated phenolics) [32], 비페닐(biphenyls) 장미과 식물에서 디벤조푸란(36), 미나리과 식물에서 잔토톡신과 6-메톡시멜레인(34,35), 그리고 마지막으로 포도과 식물(표 1)에서 하이드록시스틸벤(1,9,10)이 발견되었습니다.

3. Main Biosynthetic Pathways

Various pathways are utilized for producing different phytoalexins. As it is not our goal to describe each of these biosynthetic routes in details, we will simply outline the three most characteristic ones:

• (i)
• (ii)
• (iii)

3.1. Phytoalexins Deriving from the Phenylpropanoic-Polymalonic Acid Route

All flavonoid phytoalexins (isoflavonoids, isoflavones, pterocarpans, isoflavans, coumestans and arylbenzofurans) as well as stilbene phytoalexins and derivatives (dihydrophenanthrenes) are formed through the universal phenylpropanoic-polymalonic acid pathway. It begins with phenylalanine and the phenylalanine ammonia lyase (PAL) or to a lesser extent with tyrosine and the tyrosine ammonia lyase (TAL). The obtained para-coumaric acid is activated in para-coumaroyl-CoA by ligation to a coenzyme A by 4-coumaroyl:CoA ligase (C4L). Subsequently, chalcone synthase (CHS) on the one hand and stilbene synthase (STS) on the other hand use this same substrate and condense it with three successive units of malonyl-CoA, leading respectively to the production of naringenin chalcone, the first C15 intermediate in the flavonoid pathway and resveratrol, the precursor of all stilbenes. The possible biosynthetic routes to the main flavonoid and stilbene-like phytoalexins from the Leguminosae family are illustrated in Figure 1 [10,38,39].

Figure 1.

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Biosynthetic pathways to the main flavonoid and stilbenoid phytoalexins from the Leguminosae family. (adapted from [10,38,39]). The dashed arrows represent hypothetical steps and the solid arrows denote reactions for which the catalyzing enzymes have been cloned.

3.2. Meval‎onoid-Derived Phytoalexins

These phytoalexins are represented by members of the monoterpene, sesquiterpene, carboxylic sesquiterpene and diterpene families. Specific attention will be given to the diterpene phytoalexin class [8]. This assumption has been confirmed by the observed synchronous accumulation of seven MEP pathway gene transcripts (OsDXS3, OsDXR, OsCMS, OsCMK, OsMCS, OsHDS and OsHDR) in elicitor-induced rice (Oryza sativa) cells and the next steps of this biosynthesis are predicted to occur in plastids. Diterpenoids result from the subsequent action of diverse enzymes using GGDP as the starting block. Class II diterpene cyclases named copalyldiphosphate synthases (CPS) are the first to act on GGDP catalyzing the initial cyclization of the latter to copalyldiphosphate (CDP). CDP is the required substrate for class I diterpene synthases named kaurene synthase like (KSL). Sequential action of CPS and KSL produces the olefin precursors of the main diterpene phytoalexin families [8]. Stereochemically differentiated isomers are used subsequently by KSL: the ent-CDP in the biosynthesis of phytocassanes A-E and oryzalexins A-F and the syn-CDP in the construction of momilactones A and B (Figure 2). Further additions of oxygen in the formation of oryzalexins, momilactones and phytocassanes require a series of cytochrome P450 (CYPs) (Figure 2).

Figure 2.

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Biosynthetic pathway of diterpenoid phytoalexins.

3.3. Indole Phytoalexins

Specific attention will be paid in this section to camalexin, the major phytoalexin of Arabidopsis. The indolic ring of camalexin is derived from tryptophan (Trp) which in turn arises from chorismate (Figure 3). The first step in the route from Trp to camalexin is under the control of two cytochrome P450 homologues CYP79B2 and CYP79B3, leading to indole-3-acetaldoxime. The latter is then transformed into indole-3-acetonitrile (IAN) via the cytochrome P450, CYP71A13. Subsequent conjugation of IAN with glutathione is performed by the combined action of a glutathione-S-transferase and most likely a cytochrome P450. The IAN glutathionyl derivative is then converted into IAN cysteinyl-glycine via a phytochelatin synthase or into γ-glutamyl-cysteine IAN through the action of two γ-glutamyltranspeptidases 1 and 3 [2]. Both intermediates lead to the IAN cysteine conjugate. The last steps of this biosynthesis pathway are under the control of a CYP71B15 (PHYTOALEXIN DEFICIENT 3, PAD 3) gene encoding a multifunctional enzyme which forms camalexin via dihydrocamalexic acid (Figure 3).

3.3. 인돌 피토알렉신

이 섹션에서는 아라비도스의 주요 피토알렉신인 카말렉신에 대해 자세히 살펴볼 것입니다.

카말렉신의 인돌 고리는

트립토판(Trp)에서 유래하며,

트립토판은 다시 코리스테인(그림 3)에서 유래합니다.

트립토판에서 카말렉신으로 가는 경로의 첫 번째 단계는

두 개의 사이토크롬 P450 동족체 CYP79B2와 CYP79B3의 통제하에 진행되어 인돌-3-아세탈독심을 생성합니다.

이 후, 사이토크롬 P450인 CYP71A13을 통해

인돌-3-아세토니트릴(IAN)로 변환됩니다.

그 후 글루타티온과 IAN의 결합은

글루타티온-S-트랜스퍼라제(glutathione-S-transferase)와

시토크롬 P450(cytochrome P450)의 결합 작용에 의해 수행됩니다.

그런 다음 IAN 글루타티오닐 유도체는

피토첼라틴 신타제(phytochelatin synthase)를 통해

IAN 시스테닐-글리신(IAN cysteinyl-glycine)으로 전환되거나,

두 개의 γ-글루타밀트랜스펩티다제 1과 3[2]의 작용을 통해

γ-글루타밀-시스테인 IAN으로 전환됩니다.

두 중간체 모두 IAN 시스테인 접합체로 이어집니다.

이 생합성 경로의 마지막 단계는

디하이드로카말렉산(dihydrocamalexic acid)을 통해

카말렉신을 형성하는 다기능 효소를 암호화하는

CYP71B15(PHYTOALEXIN DEFICIENT 3, PAD 3) 유전자의 제어하에 있습니다(그림 3).

Figure 3.

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Biosynthetic pathway from tryptophan to camalexin (adapted from [2]).

4. Regulation Networks

Phytoalexin biosynthesis is up- or downregulated by expression‎ of many endogenous molecules such as phytohormones (jasmonic acid, salicylic acid, ethylene, auxins, abscisic acid, cytokinins and to a lesser extent gibberellins), transcriptional regulators, defense-related genes, phosphorylation relays and cascades [1,2].

Regulatory mechanisms of phytoalexin biosynthesis also depend on the nature of the infecting pathogen as well as the nature of the induced phytoalexin itself. For example, in the Arabidopsis-Alternaria brassicicola interaction, accumulation of camalexin was reported to be independent from jasmonic acid (JA) [40,41] though JA was involved in the regulatory signaling pathways of this phytoalexin in Arabidopsis plants challenged with the fungal pathogen Botrytis cinerea [42]. Similarly, existence of JA-dependent and independent pathways in the modulation of diterpenoid phytoalexins in the interaction between rice and the fungal agent Magnaporthe oryzae was clearly evidenced by the use of rice mutants [43]. These mutants lacking a functional allene oxide cyclase required for JA production were impaired in momilactone accumulation upon fungal infection whereas phytocassane production was not altered.

Besides, regulation of camalexin production in Arabidopsis is controlled by either salicylic acid (SA)-independent [44,45] or SA-dependent signaling pathways [46]. Indeed, biosynthesis of this phytoalexin was also found to be lower in SA-induction deficient mutants of Arabidopsis with impaired production of ethylene upon bacterial infection by Pseudomonas syringae [47].

Other phytohormones have been involved in the regulatory mechanisms of phytoalexin biosynthesis. Auxins and abscisic acid (ABA) generally appear to negatively regulate phytoalexin production [1]. Suppression of auxin signaling has recently been shown to increase the resistance of Arabidopsis to biotrophic pathogens and to redirect phytoalexin metabolism [48]. The biosynthesis of numerous phytoalexins is downregulated by ABA. For example, synthesis of kievitone in bean [49], synthesis of glyceollin in soybean [50,51] and production of rishitin and lubimin in potato [52] are all decreased by ABA. Tobacco mutants deficient in ABA exhibit twice as much capsidiol as wild-type plants [53]. In contrast, cytokinin overexpression‎ was shown to enhance resistance of tobacco to P. syringae [54]. This increased resistance correlated well with the up-regulated synthesis of two phytoalexins, capsidiol and scopoletin.

Mitogen-Activated Protein Kinases (MAPKs) have been involved in the induction of camalexin accumulation in Arabidopsis plants upon treatment with Microbe-Associated Molecular Patterns (MAMPs) [12]. Specifically two MAP kinases, MPK3 and MPK6 take part in the up-regulation of numerous enzymes of the camalexin biosynthetic route. For example, expression‎ of the CYP71B15 gene, which encodes the multifunctional enzyme acting at the end of the pathway showed a 400-fold increase upon overexpression‎ of these two MAPKs [12]. In Arabidopsis mpk3/mpk6 double mutants, camalexin production was completely abolished concomitantly with an increased susceptibility to B. cinerea.

Protein phosphorylation-induced phytoalexin production is also under the control of cell calcium transfers which in turn are decoded and transmitted by a toolkit of calcium binding proteins [1]. Several families of calcium sensors are indeed involved in the phytoalexin regulation networks. For instance, overexpression‎ of two genes encoding a calcineurin B-like protein-interacting protein kinase in rice was found to induce two phytoalexin classes, phytocassanes and momilactones upon MAMP treatment [55].

Other regulators of phytoalexin biosynthesis have been identified [1]. Overexpression‎ of Rac proteins in rice induced disease resistance to bacterial blight together with a 19- to 180-fold increase in the accumulation of the rice phytoalexin momilactone A [56]. Production of this phytoalexin is also controlled by selenium-binding protein homologues as shown in the interaction between rice and both the rice blast fungus and the rice bacterial blight [57]. Overexpression‎ of microbial virulence factors belonging to the Nep1-like protein family in Arabidopsis was associated with a strong transcriptional activation of genes involved in the camalexin route [58]. Various sugars (sucrose, glucose and fructose) acting as endogenous signals, have been reported to regulate the biosynthesis and accumulation of some phytoalexins [59]. Finally, overexpression‎ of non-expressor of pathogenesis-related genes-1 which play a critical role in the systemic acquired resistance was reported to induce the biosynthesis of the cotton phytoalexin gossypol [60]. Knowledge of the regulatory mechanisms of phytoalexin biosynthesis thus paves the way for metabolic engineering of plants for disease resistance (see Section 6).

5. Biological Activity against Microorganisms

Are phytoalexins biologically active compounds? Do phytoalexins show antibacterial activities? Over 70 years after their discovery, the actual role of phytoalexins in plant defense mechanisms is still debated. Phytoalexins are considerably less toxic than chemical fungicides. Lack of activity of isoflavonoid phytoalexins was indeed reported in comparison to classic fungicides like benomyl and mancozeb [61]. Effective doses of phytoalexins generally fall within orders of magnitude 10−5 to 10−4 M [62,63]. Phytoalexin fungitoxicity is clearly evidenced by the inhibition of germ-tube elongation, radial mycelial growth and/or mycelia dry weight increase, as best illustrated by the action of resveratrol on B. cinerea, the causal agent for gray mold in grapevine [63,64]. Phytoalexin antifungal activity can considerably vary from one compound to another. For example, Hasegawa et al., show that the rice phytoalexin sakuranetin displays a higher activity against the blast fungus than does another rice phytoalexin, momilactone A, both in vivo and in vitro [65].

Phytoalexins may also exert some effects on the cytological, morphological and physiological characteristics of fungal cells. The activity of four phytoalexins from the Solanaceae family (rishitin, phytuberin, anhydro-β-rotunol and solavetivone) on three Phytophthora species resulted in loss of motility of the zoospores, rounding-up of the cells associated with some level of swelling, cytoplasmic granulation and bursting of the cell membrane [66]. The two latter are very general features of the action of phytoalexins on fungal cells ([63,64,67] and references therein). The extensive membrane damage occurring after fungal exposure to phytoalexins is reflected in substantial leakage of electrolytes and metabolites [68]. However, it has been observed that despite the presence of wyerone acid or resveratrol, surviving B. cinerea fungal cells could produce secondary and to a lesser extent tertiary germ tubes suggesting that some sort of escape from phytoalexin damage could take place [63,69]. Asymetric growth of the germ tube resulting in the production of “curved-germ tubes” has also been observed in B. cinerea conidia treated with sub-lethal doses of resveratrol [63]. This cytological abnormality suggests that stilbenic compounds may interact with tubulin polymerization, the mode of action of many synthetic fungicides and anticancer agents [70]. Moreover, phytoalexins may affect glucose uptake by fungal cells as reported in the interactions between phaseollin or kievitone/and Rhizoctonia solani [68]. Observations of B. cinerea conidia showed a complete disorganization of mitochondria and disruption of the plasma membrane upon treatment with the stilbene phytoalexins, resveratrol and pterostilbene [63,64,67]. Pterostilbene especially led to a rapid and complete cessation of respiration in B. cinerea conidia which can be explained by its activity as an uncoupling agent of electron transport and phosphorylation [67]. Camalexin has recently been involved in the induction of fungal apoptotic programmed cell death in B. cinerea [71]. The efficaciousness in vivo of some phytoalexins, namely the coumarin phytoalexin, scopoletin on the reduction of green mold symptoms caused by Penicillium digitatum on oranges was shown [72]. In the same way, phenolic phytoalexins (resveratrol, scopoletin, scoparone and umbelliferone) were shown to significantly inhibit the growth of Penicillium expansum and patulin accumulation in apples [73]. To increase the fungitoxicity of phytoalexins, design and synthesis of more active phytoalexin derivatives is needed [74,75].

Beside their antifungal activity, phytoalexins possess some antibacterial activity. Rishitin for instance decreased the viability of cells of Erwinia atroseptica by around 100% at a dose of 360 μg/L [76]. Resveratrol also exerts some activity against numerous bacteria affecting humans: Chlamydia, Helicobacter, Staphylococcus, Enterococcus, Pseudomonas and Neisseria ([14] and references therein). It is thus clear that phytoalexins exhibit toxicity across much of the biological spectrum, prokaryotic and eukaryotic.

6. Engineering of Phytoalexins and Role in Plant Defense Mechanisms

Gain- or loss-of-function genetic approaches addressing phytoalexin production for disease resistance have provided direct and indirect proofs of their implication in plant/microorganism interactions. Relatively simple genetic constructs involving the introduction of a single gene in plants are required in the case of the grapevine phytoalexin resveratrol, synthesis of which is controlled by the stilbene synthase (STS). The first report of increased disease resistance resulting from foreign phytoalexin expression‎ in a novel plant was brought by the group of Kindl with the transfer of two grapevine STS genes (Vst 1 and Vst 2) into tobacco [77]. Introduction of these two genes was shown to confer higher resistance to B. cinerea. From that point, a number of transformations were then completed in alfalfa, rice, barley, wheat, tomato, papaya and Arabidopsis using the same STS genes or STS genes from other plant origins, conferring resistance to various pathogens [1]. All these results clearly showed that phytoalexins could act as determinant factors in the expression‎ of the defense mechanisms of plants against phytopathogenic microorganisms though there are rare examples of STS overexpression‎ not being associated with disease resistance [1].

Following the works on stilbene phytoalexins, other genetic transformations were achieved with other phytoalexin genes. Surprisingly, engineering phytoalexins seems to have been limited to exploiting only a few phytoalexin biosynthetic genes. This has mainly concerned the genetic manipulation of phytoalexin glycosylation by the use of a tobacco glucosyltransferase acting on scopoletin [78]. Overexpression‎ of the isoflavonoid-7-O-methyltransferase in alfalfa, an enzyme with a crucial role in the biosynthesis of the phytoalexin maiackiain, was also linked to an increased resistance of that plant to Phoma medicaginis [79]. Transformation of soybean hairy roots with both the peanut resveratrol synthase 3 AhRS3 gene and resveratrol-O-methyltransferase ROMT gene catalyzing the transformation of resveratrol to pterostilbene [80] resulted in the resistance of that plant to Rhizoctonia solani [81]. In many cases, engineering the entire phytoalexin biosynthetic pathway is not feasible and the problem researchers are facing is to choose the right enzyme catalyzing the limitant step of this pathway.

Loss-of-function genetic approaches clearly evidenced the role played by phytoalexins in plant-microorganism interactions. In almost all experiments, mutants impaired in phytoalexin production showed increased susceptibility to pathogens. Reduced amounts of pisatin in hairy roots of pea transformed with antisense 6-α-hydroxymaiackiain-3-O-methyltransferase were associated with a decreased resistance to the fungal pathogen Nectria haematococca [17]. RNAi silencing of isoflavone synthase or chalcone reductase in soybean suppressed by 90% the accumulation of daidzein and glyceollin as well as disease resistance to P. sojae [82]. Loss-of-function alleles of the yellow seed1 gene encoding CHS, chalcone isomerase, dihydroflavonol reductase and flavonoid-3'-hydroxylase induced deficiency in the accumulation of 3-deoxyanthocyanidin associated with severe symptoms of the anthracnose disease in sorghum [83]. Effect of the PHYTOALEXIN DEFICIENT mutation on camalexin in Arabidopsis was found to be dependent on the infecting pathogen. This mutation was not associated with increased susceptibility to P. syringae, Perenospora parasitica, Erysiphae oronti and B. cinerea though it markedly affected its susceptibilty to A. brassicicola ([1] and references therein). Finally loss-of-function genetic approaches have underlined the role of phytoalexin glycosylation in plant-pathogen interactions. Transgenic tobacco leaves downregulated for a tobacco specific phenylpropanoid glucosyltransferase saw their scopolin content decreased by 70% to 75% associated with a 63% increase in TMV lesion surfaces [84].

Indirect modulation of phytoalexin levels through manipulation of hormone signaling, phosphorylation cascades or defense-related marker genes also demonstrated the role of phytoalexins in plant defense mechanisms. For instance cytokinin overexpression‎ in tobacco led to increased resistance to P. syringae which strongly correlated with up-regulated synthesis of two phytoalexins, capsidiol and scopoletin [54]. Mutations in two MAP kinases MPK3 and MPK6 impaired camalexin production and disease resistance to B. cinerea in Arabidopsis [12].

Though phytoalexin engineering seems to have been limited to exploiting only a few genes mainly stilbene and isoflavonoid ones, indirect modulation of phytoalexin accumulation employing transcriptional regulators or components of upstream regulatory pathways becomes a useful approach to improve plant disease resistance [1].

7. Fungal Metabolism and Transporters

The interaction between a plant and its pathogen can be envisaged as a balance between phytoalexin production by the host and phytoalexin metabolism or inactivation via transporters (mainly ATP Binding Cassette, ABC transporters) by the second actor of this interaction. Modification of any of the factors contributing to this balance could modify the outcome of the interaction. We will further see that in phytopathogenic fungi, ABC transporters act as virulence factors, conferring protection against defense compounds produced by the host. In several plant-fungus interactions, it has become evident that the ability to weaken or neutralize the effects of phytoalexins is one of the essential determinants of fungal/host coupling. Detoxification processes of phytoalexins by fungi are far from being clearly understood [85].

It is rather difficult to derive any comprehensive generalizations from the existing data on phytoalexin metabolism per se. The known catabolic pathways of phytoalexins by fungi may involve monoxygenation, reduction, hydration, oxidation, oxidative dimerization, glycosylation and demethylation reactions. Since most phytoalexins are lipophilic compounds that efficiently penetrate cell membrane structures, phytoalexin metabolism usually involves their conversion to more polar products. Creation of new hydroxyl groups by oxygenation, demethylation, reduction of aldehydes and ketones or hydration of double bonds as well as glycosylation increase the degree of polarity of phytoalexins. Detoxification of the cruciferous phytoalexins, brassinin, 1-methoxybrassinin and cyclobrassinin, by the stem rot fungus Sclerotinia sclerotiorum indeed requires a brassinin glucosyltransferase [86]. Methylated phytoalexins are well known to be more fungitoxic than the non-methylated ones owing to the fact that phytoalexin methylation enhances their lipophilic character. Moreover the presence of methylated groups or any other electron-attracting groups on the aromatic ring of some phytoalexins plays an important role in the formation of charge transfer complexes, favoring contact and affinity with (membrane) proteins and acting as uncoupling agents of electron transport and photophosphorylation. A cytochrome P450 pisatin demethylase transforming pisatin into 6-α-hydroxymaiackiain and 3-hydroxymaackiain-isoflavan was characterized from the fungal pathogen Nectria haematococca [87]. Interestingly, fungal isolates with the highest pisatin demethylating activity were shown to be the most virulent on pea [87]. In addition, overexpression‎ of this pisatin demethylating activity in hairy roots of pea resulted in reduced amounts of this phytoalexin in the plant tissues upon infection by N. haematococca with a correlated decreased resistance to this pathogen [17]. Two hydratases, a kievitone hydratase from Fusarium solani [88] and one inducible hydrolase of Leptosphaeria maculans acting on brassinin [89] were implicated in the detoxification process of these two phytoalexins.

Oxidation and oxidative dimerization processes can also take place in the metabolism of phytoalexins. A brassinin detoxifying oxidase with a molecular mass of 57 kDa has been characterized and purified from the blackleg fungus L. maculans. This oxidase transforms the cruciferous phytoalexin brassinin into the less fungitoxic compound indol-3-carboxaldehyde [90]. Interestingly, this pathogen was unable to metabolize camalexin, another major phytoalexin from crucifers, conferring this plant family protection against L. maculans. Simple stilbenes produced by members of the Vitaceae family may undergo oxidative dimerization by a laccase-like stilbene oxidase from B. cinerea with a molecular mass of 32 kDa [91]. This process involves the 4'-hydroxyphenyl group of one resveratrol unit leading to a dehydrodimer with a dihydrobenzofuran structure named δ-viniferin [92,93]. Importantly, B. cinerea isolates possessing the highest oxidative activity were found to be the most virulent on grapevine [94]. Very recently, the stilbene-type phytoalexin astringin produced by Norway spruce in the interaction with the bark beetle (Ips spp.) and its fungal associate, Ceratocystis polonica was shown to undergo metabolism by the latter [95]. C. polonica converted astringin to ring-opened lactones, aglycones and dehydrodimers in vitro. In this study, the virulence of the fungal pathogen on Norway spruce correlated well with differential usage of the various pathways for stilbene biotransformation.

Phytopathogenic fungi evolved mechanisms of insensitivity or resistance to protect themselves against phytoalexins. One of them involves extruding toxic compounds out of the cell through transporters, conferring them protection against plant defense products. In fungi, the role of ATP-binding cassette (ABC) transporters in the efflux of natural and synthetic toxicants is well known [96,97,98]. In addition, several genes encoding ABC transporters have been shown to be involved in fungal virulence on plant hosts [99,100,101,102,103,104]. A number of phytoalexins and other toxic compounds induced expression‎ of these fungal transporters [99,100,105,106,107]. However, only a few studies have demonstrated the ability of these transporters to confer tolerance to a known phytoalexin. In B. cinerea, the BcatrB ABC transporter has been shown to be a virulence factor that increases tolerance of the pathogen towards phytoalexins. Indeed, BcatrB replacement mutants revealed increased sensitivity to resveratrol and reduced virulence on grapevine leaves [100]. Moreover, a B. cinerea strain lacking functional BcatrB was more sensitive to camalexin in vitro and less virulent on A. thaliana wild-type plants, but was fully virulent on camalexin-deficient A. thaliana mutants [103]. In the same way, ABC transporters related to BcatrB, such as GpABC1 from Gibberella pulicaris, act as virulence factors on potato. GpABC1 provides tolerance to rishitin, while a GpABC1 mutant is essentially non-pathogenic [101]. In N. haematococca, the NhABC1 gene is induced after treatment with pisatin in vitro and during infection of pea plants. Mutation in NhABC1 gene rendered the fungus even more sensitive to pisatin and led to lower pathogenicity on pea, indicating that NhABC1 contributes to the tolerance to pisatin and acts as a virulence factor [102]. The substrate range of ABC transporters can vary from a single compound to a wide spectrum of molecules with no identified common feature. BcatrB from B. cinerea has a wide substrate range, comprising mainly aromatic compounds [100,103,107,108,109] such as the phytoalexins eugenol, resveratrol and camalexin, the fungicides fenpiclonil and fludioxonil, as well as the antibiotics phenazine-1-carboxylic acid and phenazine-1-carboxamide. The closest identified homologue of BcatrB, AtrB from Aspergillus nidulans, shows a similar function in multidrug resistance [110]. Two other homologues with similar substrate ranges are MgAtr5 from Mycosphaerella graminicola [111] and PMR5 from Penicillium digitatum [112], indicating that other homologues of BcatrB may function also in multidrug resistance and pathogenesis. Taken together, it becomes evident that ABC transporters can be essential for the development of phytopathogenic fungi, providing protection against phytoalexins produced by the host plant and acting as virulence factors.

8. Role of Phytoalexins in Human Health

Phytoalexins may display health-promoting effects in humans. A few of them have been reported to exert antioxidant, anticarcinogenic and cardiovascular protective activities. Maslinic acid, a natural phytoalexin-type triterpene from olives exerts a wide range of biological activities as an antitumor, antidiabetic, neuroprotective, cardioprotective, antiparasitic and growth-stimulating agent, providing evidence of the potential of this molecule as a nutraceutical [113]. Health benefit properties of Brassicaceae were attributed in part to their phytoalexins, camalexin and related indolic compounds [114]. Camalexin namely is able to induce apoptosis in prostate cancer cells [115]. 3-deoxyanthocyanidins, flavonoid phytoalexins produced by members of the Poaceae family, are helpful in reducing the incidence of gastro-intestinal cancer [116]. Moreover, other indolic phytoalexins such as brassinin and its derivative, homobrassinin, show marked antiproliferative activities in human colorectal cancer cells in vitro [117]. The most promising results in this area were obtained with resveratrol, the phytoalexin from grapevine. This compound is indeed considered to be an antiproliferative agent exerting antitumor activity either as a cytostatic or a cytotoxic agent in various cancers [118]. The first report of the cancer chemoprotective activity of a phytoalexin is the study of the group of Pezzuto [119]. This pioneering work was then confirmed on many other human cancer models. The most frequently described mode of antitumor action for phytoalexins concerns apoptosis which may be via the inhibition of antiapoptotic molecules such as survivin [120] or, for instance as reported in this issue, alterations of expression‎ and activity of lysosomal protease cathepsin D [115].

Resveratrol exerts antitumor activities in vivo, namely in skin cancers by topical applications. It does not seem to be very effective in inhibiting leukemia despite displaying antileukemic activity in vitro and shows anticancer effects in experimentally-induced breast cancers only at high doses. Resveratrol presents some anticancer activities in hepatoma, lung carcinoma and intestinal tumors ([14] and references therein). However lack of efficacy of natural phytoalexins in reducing tumors has led to a number of investigations regarding the design and synthesis of more potent anticancer derivatives of known phytoalexins such as brassinin [121], methoxybrassinol [122] and resveratrol [123].

There are also several studies providing evidence of the cardioprotective activity of phytoalexins such as indoles and stilbenes [14,114]. Resveratrol namely was proven to inhibit LDL peroxidation in ex vivo rat heart studies, to have a potent role in preventing atherosclerosis and to block platelet aggregation from high-cholesterol-fed rabbits ([14] and references therein). Besides, this compound has an effect in neurological diseases such as cerebral ischemia, Parkinson’s disease, pain and cognitive impairment in rats, spinal cord lesion in rabbits and finally brain edema and tumors in human cells ([14] and references therein). Interestingly, additional studies have also demonstrated that resveratrol increases lifespan in lower organisms (yeast, metazoans) and higher organisms through the activation of the sirtuin proteins [124,125]. Resveratrol’s mechanisms of action are likely to be pleitropic and mediated by the interaction of this compound with key signaling proteins controlling cellular calcium homeostasis [126]. Interestingly, quercetin and umbelliferone were also reported to reduce mycotoxin accumulation in apple fruits by P. expansum by down-regulating relative expression‎ of genes encoding patulin biosynthesis [127].

Some other phytoalexins like the steroid glycoalkaloids from potato or the dimeric sesquiterpene gossypol from cotton display a certain level of toxicity for humans explaining the crucial interest in engineering those plants for abolishing production of these undesirable compounds [11,128].

8. 인체 건강에 있어서 피토알렉신의 역할

피토알렉신은 인체 건강에 긍정적인 영향을 미칠 수 있습니다.

그 중 일부는

항산화, 항암, 심혈관 보호 작용을 하는 것으로 보고되었습니다.

올리브에서 추출한 천연 식물성 알렉신(phytoalexin) 유형의

트리테르펜인 마슬린산은

항암, 항당뇨, 신경보호, 심장보호, 항기생충, 성장 촉진 작용을 하는 등

다양한 생물학적 활성을 발휘하며,

이 분자가 기능성 식품으로서 잠재력을 가지고 있다는 증거를 제시합니다 [113].

브라시카과 식물의 건강에 유익한 성분은

부분적으로 식물 알렉신, 카말렉신 및 관련 인돌 화합물에 기인합니다 [114].

카말렉신은

전립선암 세포에서 세포 사멸을 유도할 수 있습니다 [115].

벼과 식물의 구성원이 생산하는 플라보노이드 식물 알렉신인

3-데옥시안토시아니딘은

위장암 발생률을 줄이는 데 도움이 됩니다 [116].

또한,

브라시닌과 그 유도체인 호모브라시닌과 같은 다른 인돌계 식물알렉신(phytoalexins)은

시험관 내에서 인간 대장암 세포에서 현저한 항증식 작용을 나타냅니다 [117].

이 분야에서 가장 유망한 결과는

포도나무에서 추출한 식물알렉신인 레스베라트롤을 통해 얻어졌습니다.

이 화합물은 실제로 다양한 암에서 세포 증식 억제제 또는 세포 독성제로서 항암 작용을 하는 항증식제로 간주됩니다 [118]. 식물 알렉신(phytoalexin)의 항암 화학 보호 작용에 대한 최초의 보고서는 Pezzuto 그룹의 연구입니다 [119]. 이 선구적인 연구는 이후 다른 많은 인간 암 모델에서 확인되었습니다. 식물 알렉신에 의한 항암 작용의 가장 빈번하게 설명되는 방식은 세포자멸사(apoptosis)와 관련이 있는데, 이것은 생존(survival)과 같은 항세포자멸 분자의 억제를 통해 이루어질 수 있습니다[120] 또는, 예를 들어 이번 호에서 보고된 바와 같이, 리소좀 프로테아제 카텝신 D의 발현과 활성의 변화와 관련이 있을 수 있습니다[115].

레스베라트롤은 생체 내, 즉 피부암에 국소적으로 적용할 때 항암 작용을 발휘합니다. 체외에서 항백혈병 작용을 나타내지만, 백혈병 억제에는 그다지 효과적이지 않은 것으로 보이며, 실험적으로 유발된 유방암에 대한 항암 효과는 고용량에서만 나타납니다. 레스베라트롤은 간암, 폐암, 장암에 대한 항암 작용을 나타냅니다([14] 및 그 안에 있는 참고 문헌). 그러나 천연 식물성 알렉신(phytoalexins)이 종양 감소에 효과가 없다는 사실이 밝혀지면서, 브라시닌(brassinin) [121], 메톡시브라시놀(methoxybrassinol) [122], 레스베라트롤(resveratrol) [123]과 같은 알려진 식물성 알렉신의 더 강력한 항암 유도체의 설계와 합성에 관한 많은 연구가 이루어졌습니다.

또한 인돌과 스틸벤과 같은 식물성 알렉신(phytoalexins)의 심장 보호 작용에 대한

증거를 제공하는 여러 연구가 있습니다 [14,114].

레스베라트롤은 생체 외 쥐 심장 연구에서 LDL 과산화 억제를 통해 죽상 동맥 경화 예방에 강력한 역할을 하고, 고콜레스테롤을 섭취한 토끼의 혈소판 응집을 차단하는 것으로 입증되었습니다 ([14] 및 그 안에 있는 참고 문헌). 게다가, 이 화합물은 쥐의 뇌허혈, 파킨슨병, 통증, 인지장애, 토끼의 척수 손상, 그리고 인간 세포의 뇌부종과 종양과 같은 신경학적 질병에 효과가 있습니다 ([14] 및 그 안에 있는 참고문헌). 흥미롭게도, 추가 연구에 따르면 레스베라트롤은 시르투인 단백질의 활성화를 통해 하등생물(효모, 다세포동물)과 고등생물(인간)의 수명을 늘린다는 사실이 밝혀졌습니다 [124,125]. 레스베라트롤의 작용 메커니즘은 다중적일 가능성이 높으며, 이 화합물과 세포 내 칼슘 항상성을 조절하는 주요 신호 전달 단백질 간의 상호 작용에 의해 매개될 수 있습니다 [126]. 흥미롭게도, 퀘르세틴과 움벨리페론은 또한 사과 과일에 있는 푸사리움 팽창균에 의한 마이코톡신 축적을 감소시키는 것으로 보고되었습니다. 이는 파툴린 생합성을 암호화하는 유전자의 상대적 발현을 하향 조절함으로써 이루어집니다 [127].

감자에서 추출한 스테로이드 글리코알칼로이드나 면에서 추출한 이합체 세스퀴테르펜 고시폴과 같은 다른 식물 알렉신(phytoalexins)은 인간에게 어느 정도의 독성을 나타내므로, 이러한 바람직하지 않은 화합물의 생산을 중단시키기 위해 식물을 조작하는 것에 대한 관심이 매우 높습니다 [11,128].

9. Concluding Remarks

Works on phytoalexins from diverse chemical families have generated a lot of data regarding basic aspects of plant defenses and their regulatory mechanisms. As a result, engineering of phytoalexins has arisen as a new area in the development of useful approaches to disease control. Nonetheless, while a variety of genetic transfers were carried out in order to investigate the potential of stilbene and flavonoid phytoalexin biosynthetic genes in conferring disease resistance, strategies focusing on the other phytoalexin chemical families did not [1].

Some studies have attempted to determine the actual concentration and the nature of phytoalexins directly in plant tissues in response to invading microorganisms using spectroscopic methods [129,130]. However, our general knowledge remains limited by the difficulty to analyse the events occurring under natural conditions between the plant and the pathogen.

On the other hand, the potential value of several phytoalexins on a therapeutic point of view has made their large-scale production a necessity. Engineering yeast and bacteria, may represent valuable means for the production of phytoalexins at an industrial scale [14,131]. However, their tailoring is needed as they do not possess the genes encoding phytoalexin biosynthesis. Another approach is large-scale production of phytoalexins using plant cell suspensions in bioreactors. Some experiments are underway to optimize stilbene phytoalexin production in bioreactors [132,133].

Although considerable work has already been done on phytoalexins, the ways in which they act against microorganisms and the mechanisms the latter have developed to counteract their action are still poorly understood keeping this subject an active field of research even after over 70 years.

AbbreviationIFS

2-hydroxy isoflavanone synthase;

DMI

7,2'-dihydroxy-4'-methoxy-isoflavanol;

DMDI

7,2'-dihydroxy-4',5'-methylenedioxy-isoflavanol;

HMM

6α-hydroxymaackiain 3-O-methyltransferase

HI4'OMT: SAM:

2,7,4'-trihydroxy-isoflavanone 4'-O-methyltransferase;

STS

stilbene synthase;

CHS

chalcone synthase.

Author Contributions

Philippe Jeandet wrote the paper. Marie-Alice Deville edited the whole manuscript. Aziz Aziz, Stephan Dorey and Sylvain Cordelier checked the regulatory and molecular engineering sections. Claire Hébrard and Jérôme Crouzet wrote the ABC transporter section.

Conflicts of Interest

The authors declare no conflict of interest.

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