摘要:植物促生菌具有抗病和促生的潛能,在農(nóng)業(yè)生產(chǎn)及環(huán)境保護(hù)方面都具有重要的作用。在許多革蘭氏陰性細(xì)菌中,N-乙酰基高絲氨酸內(nèi)酯(AHLs)介導(dǎo)的群體感應(yīng)(QS)系統(tǒng)不僅參與對(duì)細(xì)菌多種生理行為和生物學(xué)功能的調(diào)控,而且影響植物基因的表達(dá)及細(xì)菌與宿主植物間的互作。為了更好地開(kāi)發(fā)利用生防菌,綜述了多年來(lái)對(duì)AHLs跨界信號(hào)轉(zhuǎn)導(dǎo)參與調(diào)節(jié)植物生長(zhǎng)發(fā)育和抗逆性的研究,并對(duì)該領(lǐng)域今后的研究方向進(jìn)行了展望,以期為改善植物抗逆性和促進(jìn)生長(zhǎng)提供一些新思路。
關(guān)鍵詞:N-乙?;呓z氨酸內(nèi)酯(AHLs);群體感應(yīng);信號(hào)轉(zhuǎn)導(dǎo);生長(zhǎng)發(fā)育;抗逆
中圖分類號(hào):Q935 文獻(xiàn)標(biāo)識(shí)碼:A 文章編號(hào):0439-8114(2016)14-3537-06
DOI:10.14088/j.cnki.issn0439-8114.2016.14.001
Abstract: With the development of biological control, people pay more and more attention to plant promoting bacteria, which can be used as biological agent against most of fungi pathogens play an important role in agricultural production and environmental protection. In most of gram negative(G-) bacteria, N-acylhomoserine lactones (AHLs)-mediated quorum-sensing (QS) systems is not only involved in the regulation of various physiological behavior and biological function, but also affect the interaction between bacterial and host plants and the expression of plant genes. In order to better exploit and utilization of biocontrol bacteria, this paper summarized the studies of AHLs regulating plant growth and resistance by crossover signal transduction,while the prospects are forecasted in order to provide some new ideas for the improvement of plant resistance and growth, and hoping to improve the plant resistance and promote growth to provide some new ideas.
Key words: N-acyl-homoserine lactone; quorum sensing; signal transduction; plant development; resistance
隨著生物防治的發(fā)展,植物促生菌日益引起人們的關(guān)注。它可以促進(jìn)植物的生長(zhǎng),提高植物的抗逆性,增強(qiáng)植物抵抗病原菌的能力,在農(nóng)業(yè)生產(chǎn)及環(huán)境保護(hù)方面都具有重要的作用,因此如何更好地利用這些細(xì)菌來(lái)保護(hù)植物也逐漸成為研究的焦點(diǎn)。許多革蘭氏陰性菌利用N-乙?;呓z氨酸內(nèi)酯 (N-acyl-homoserine lactones,AHLs)作為胞間信號(hào)分子改變和協(xié)調(diào)細(xì)菌群體基因的表達(dá),協(xié)同調(diào)節(jié)種群的某些生理特性和行為,以及與動(dòng)植物寄主/宿主的互作,從而實(shí)現(xiàn)單個(gè)細(xì)菌無(wú)法完成的某些生理功能和調(diào)節(jié)機(jī)制。這一調(diào)控系統(tǒng)被稱為細(xì)菌的群體感應(yīng)調(diào)節(jié)(Quorum sensing,QS)[1-3]。
AHLs依賴的QS機(jī)制最先在海洋細(xì)菌費(fèi)氏弧菌(Vibrio fischeri)的研究中發(fā)現(xiàn),V. fischeri是一種海洋發(fā)光菌,具有熒光素酶的結(jié)構(gòu)基因(靶基因)LuxCDABE, 群體感應(yīng)的調(diào)控機(jī)制需要兩種組分參與:LuxI蛋白與LuxR蛋白。其中,LuxI蛋白負(fù)責(zé)信號(hào)分子AHLs的合成,而LuxR蛋白則結(jié)合AHLs并激活熒光素酶基因的轉(zhuǎn)錄。人們發(fā)現(xiàn)當(dāng)V. fischeri菌體濃度上升的同時(shí),會(huì)伴隨著AHLs分子濃度的增加,而當(dāng)AHLs濃度達(dá)到微摩爾級(jí)范圍時(shí),就會(huì)與LuxR蛋白結(jié)合,結(jié)合復(fù)合物再去激活熒光素酶基因的啟動(dòng)子轉(zhuǎn)錄,表現(xiàn)為發(fā)出肉眼可見(jiàn)的光[4,5]。同時(shí),AHLs分子與受體蛋白的復(fù)合體也對(duì)AHLs分子及受體蛋白本身的產(chǎn)生具有反饋調(diào)節(jié)效應(yīng)。多年來(lái),V. fischeri的LuxI/LuxR雙元件系統(tǒng)一直被視為群體感應(yīng)的經(jīng)典(圖1)。目前,已經(jīng)在70多種不同的革蘭氏陰性菌中發(fā)現(xiàn)了相似或同源的QS系統(tǒng)[6,7]。不同細(xì)菌的QS系統(tǒng)可以產(chǎn)生不同的信號(hào)分子,調(diào)節(jié)多種功能,如可影響細(xì)菌毒力因子的產(chǎn)生[8]、生物發(fā)光[4]、生物膜形成[9]、胞外酶和次生代謝物的生物合成[10]、共生現(xiàn)象[11]、孢子形成[12]以及質(zhì)粒結(jié)合和轉(zhuǎn)移等[13]。在QS參與調(diào)控的很多生物學(xué)功能中,對(duì)病原菌毒性因子的表達(dá)和生物膜形成的調(diào)控是目前備受關(guān)注的熱點(diǎn)問(wèn)題。由于微生物與植物之間互作的復(fù)雜性,目前對(duì)生防細(xì)菌QS的探索還集中在對(duì)其調(diào)控機(jī)理的研究[7]。
AHLs介導(dǎo)的細(xì)菌QS系統(tǒng)不僅參與細(xì)菌多種生理行為和生物學(xué)功能的調(diào)控,還影響真核生物基因的表達(dá)。近幾年,許多證據(jù)表明植物進(jìn)化出許多方式感知和響應(yīng)QS信號(hào)AHLs[14,15]。當(dāng)AHLs在植物周圍存在時(shí),可以引起植物基因和蛋白表達(dá)的變化。目前關(guān)于單個(gè)細(xì)菌AHLs影響的研究多來(lái)自無(wú)菌的植物體系,外源施加少量純的QS信號(hào)分子。本文結(jié)合近年來(lái)AHLs與植物之間跨界信號(hào)轉(zhuǎn)導(dǎo)的研究進(jìn)展,著重闡述細(xì)菌AHLs對(duì)植物防御和發(fā)育的影響,以及不同的AHLs在植物環(huán)境中的去向,以期為優(yōu)化生防菌并利用細(xì)菌群體感應(yīng)調(diào)節(jié)信號(hào)作為新型植物生長(zhǎng)調(diào)節(jié)劑改善作物產(chǎn)量和品質(zhì)提供一些新思路。
1 QS信號(hào)分子AHLs
細(xì)菌的群體感應(yīng)是由細(xì)菌自身合成并分泌到環(huán)境中的一些特殊、微小、可擴(kuò)散的有機(jī)化學(xué)分子介導(dǎo)的,這些物質(zhì)被稱為自誘導(dǎo)物(Autoinducer) 或信號(hào)素(Pheromone)。截至2006年,科學(xué)家對(duì)近百種微生物的QS進(jìn)行了深入研究,發(fā)現(xiàn)有多種與微生物群體感應(yīng)相關(guān)的化學(xué)信號(hào)分子。其中AHLs及其衍生物作為信號(hào)分子主要作用于革蘭氏陰性細(xì)菌,如V. fischeri 中的LuxI/LuxR生物發(fā)光系統(tǒng),AHLs分子在費(fèi)氏弧菌中與LuxR受體蛋白結(jié)合,促進(jìn)發(fā)光酶基因的表達(dá)[4];軟腐歐文氏菌(Erwinia carotovora)中的ExpI/ExpR-CarI/CarR毒性/抗生素表達(dá)系統(tǒng)等[16],AHLs與ExpR受體蛋白結(jié)合促進(jìn)致病胞外酶的表達(dá),與CarR受體蛋白結(jié)合促進(jìn)碳青霉烯抗生素的產(chǎn)生,這些胞外酶及抗生素的產(chǎn)生是軟腐類病原菌成功侵入寄主并繁衍種群的關(guān)鍵因子;銅綠假單胞菌(Pseudomonas aeruginosa)中的LasI/LasR-RhlI/RhlR毒性表達(dá)系統(tǒng)等[17]。此外,脂肪酸衍生物如3-羥基棕櫚酸甲酯(3-Hydroxypalmitic acid methylester)以及一些順式不飽和脂肪酸(Cis-unsaturated fatty acids)也可作為信號(hào)分子。例如青枯菌(Ralstonia solanacearum)產(chǎn)生的3-羥基棕櫚酸甲酯,通過(guò)調(diào)控其表現(xiàn)性轉(zhuǎn)換系統(tǒng)Phc調(diào)節(jié)子的表達(dá)以適應(yīng)青枯菌的密度效應(yīng)及增殖[18]。另外,還有2-庚基-3-羥基-4-喹啉、二酮吡嗪DKP以及γ-丁酸內(nèi)酯等,在不同菌體中都能起到與AHLs類似的作用[19]。這說(shuō)明細(xì)菌QS信號(hào)分子具有復(fù)雜性和多樣性。AHLs信號(hào)分子可自由穿透細(xì)胞壁與膜并在環(huán)境中累計(jì),當(dāng)達(dá)到一定密度閾值時(shí),能與相應(yīng)受體蛋白的氨基端結(jié)合,形成特定的構(gòu)象,使羧基端能與靶DNA序列相結(jié)合,從而調(diào)控某些功能基因的表達(dá)。不同細(xì)菌的I蛋白產(chǎn)生的信號(hào)不同,這種不同主要有兩方面:一是?;湹奶挤肿拥拈L(zhǎng)度不同,碳的長(zhǎng)度由4個(gè)到18個(gè)不等;二是C3位置是否有氧取代基或者氫氧根取代基。下圖所示的就是幾種來(lái)源于革蘭氏陰性細(xì)菌的AHLs信號(hào)的分子結(jié)構(gòu)(圖2)。
2 細(xì)菌AHLs對(duì)植物防御系統(tǒng)的影響
越來(lái)越多的證據(jù)表明,細(xì)菌產(chǎn)生的AHLs以及AHLs本身可以對(duì)植物防御系統(tǒng)產(chǎn)生影響。植物也可以利用QS系統(tǒng)信號(hào)分子來(lái)誘發(fā)抗病性。2006年Schuhegger等[20]通過(guò)對(duì)番茄和液化沙雷氏菌互作的研究首次報(bào)道了AHLs對(duì)植物免疫性有重要作用,研究發(fā)現(xiàn)根際生防菌Serratia liquefaciens MG1和 Pseudomonas putida IsoF產(chǎn)生C4和C6-HSL可以誘導(dǎo)番茄中水楊酸(SA)和乙烯(ET)介導(dǎo)的防衛(wèi)反應(yīng),它們對(duì)于激活植物系統(tǒng)抗性和提高植物對(duì)黑斑病菌(Alternaria alternate)的抗性有重要作用,而液化沙雷氏菌的AHLs突變體MG44對(duì)真菌的生防能力大大降低。而后許多實(shí)驗(yàn)室通過(guò)試驗(yàn)也分別獨(dú)立地發(fā)現(xiàn)根際促生菌產(chǎn)生的AHLs或植物營(yíng)養(yǎng)液中添加的AHLs都具有調(diào)節(jié)植物防衛(wèi)的能力。相類似的,可以產(chǎn)生AHLs的普城沙雷菌在黃瓜的定殖能提高黃瓜對(duì)土傳病害終極腐霉(Pythium ultimum)的抗性,以及提高番茄和大豆對(duì)真菌灰霉菌的抗性,而AHLs產(chǎn)生受影響的splI突變體則不能[21]。不同的AHLs具有誘導(dǎo)對(duì)細(xì)菌病原物丁香假單胞菌Pseudomonas syringae pv. tomato DC3000(Pst) DC3000抗性的能力。比如oxo-C14-HSL可以顯著提高擬南芥對(duì)Pst DC3000的抗性。同樣,在植物根經(jīng)oxo-C14-HSL預(yù)處理后,可以顯著提高對(duì)活體營(yíng)養(yǎng)真菌病原菌擬南芥白粉菌以及大麥白粉菌的抗性。另外,OH-C14-HSL及oxo-C12-HSL也具有誘導(dǎo)抗性的潛力,但相比C14-HSL衍生物的能力減弱[22]。最近有研究表明oxo-C14-HSL不但可以提高農(nóng)作物包括小麥、大麥及番茄對(duì)致病菌的抗性,而且可以提高人類病原菌的抗性[23]。外源施加黏質(zhì)沙雷氏菌(Serratia marcescens)90-166后,可以產(chǎn)生AHL的轉(zhuǎn)基因番茄對(duì)病原菌的誘導(dǎo)系統(tǒng)抗性(ISR)增強(qiáng),而不能產(chǎn)生AHLs的AiiA轉(zhuǎn)基因番茄對(duì)胡蘿卜軟腐果膠桿菌(Pectobacterium carotovorum subsp. carotovorum)和煙草野火病菌(Pseudomonas syringae pv. tabaci)兩種病原菌的抗性降低,相反,AHLs轉(zhuǎn)基因植株對(duì)黃瓜花葉病毒的ISR降低,而在AiiA轉(zhuǎn)基因植株中升高,說(shuō)明S. marcescens 90-166誘導(dǎo)的QS依賴的ISR可能與病原菌的種類有關(guān)[24]。
但也有一些相反的報(bào)道,比如擬南芥根經(jīng)C4和C6短鏈AHLs預(yù)處理后并沒(méi)有提高植物系統(tǒng)抗性。一些系統(tǒng)病原物響應(yīng)的基因比如幾丁質(zhì)酶、PR1等也沒(méi)有被誘導(dǎo)[25]。Zarkani等[26]比較了分別施加兩種不同的根瘤菌對(duì)植物抗性的影響,結(jié)果發(fā)現(xiàn)可以產(chǎn)生長(zhǎng)鏈oxo-C14-HSL的苜蓿中華根瘤菌(Sinorhizobium meliloti)能提高植物對(duì)致病菌的抗性,而可以產(chǎn)生短鏈oxo-C8-HSL的埃特里根瘤菌(Rhizobium etli)對(duì)植物的抗性沒(méi)有影響。利用基因組或蛋白組學(xué)的方法,一些研究比較了植物對(duì)不同AHL的反應(yīng),結(jié)果發(fā)現(xiàn)只有長(zhǎng)鏈的AHLs可以引發(fā)抗性相關(guān)的變化[27]。因此,AHLs是否可以誘導(dǎo)系統(tǒng)反應(yīng)或在植物體內(nèi)運(yùn)輸可能取決于AHLs分子的種類,尤其是脂肪酸鏈的長(zhǎng)度及修飾,具有不同脂肪酸鏈的AHL在不同的物種中可能引發(fā)不同的響應(yīng)。
對(duì)于oxo-C14-HSL誘導(dǎo)的植物抗性可能與氧脂(Oxylipins)以及SA有關(guān)。SA是激發(fā)系統(tǒng)獲得性抗性的主要信號(hào)分子,與受侵染組織的局部抗性和未侵染組織的系統(tǒng)獲得性抗性的形成密切相關(guān),氧脂包括茉莉酸及其代謝物等都是脂源性化合物,在植物-病原物互作中,SA和JA之間存在拮抗作用[28]。Schenk等[29]發(fā)現(xiàn)經(jīng)oxo-C14-HSL預(yù)處理后,氧脂和SA信號(hào)轉(zhuǎn)導(dǎo)途徑之間存在協(xié)同作用,并且不依賴于JA信號(hào)轉(zhuǎn)導(dǎo)途徑。oxo-C14-HSL可以引起植物體內(nèi)酚類物質(zhì)和木質(zhì)素的積累以及胼胝質(zhì)在細(xì)胞壁的沉積,另外氧脂在遠(yuǎn)端組織的積累可以導(dǎo)致氣孔關(guān)閉,也可以提高植物對(duì)細(xì)菌病害的抗性[14,26,29,30]。植物的防衛(wèi)機(jī)制受到嚴(yán)格的調(diào)控并且只在病原物被識(shí)別后誘導(dǎo)。因?yàn)閷?duì)抗病反應(yīng)持續(xù)的誘導(dǎo)會(huì)打亂植物代謝,抑制植物生長(zhǎng)和發(fā)育。有絲分裂原活化蛋白激酶MPK3和MPK6是植物防御系統(tǒng)調(diào)控網(wǎng)絡(luò)中關(guān)鍵的組分[28]。在植物中,經(jīng)細(xì)菌病原物相關(guān)的分子模式flg22處理后引發(fā)對(duì)MPK3和MPK6的短暫激活,一般處理30 min后活性降低。然而,植物經(jīng)AHLs預(yù)處理后可以延長(zhǎng)對(duì)MPK3和MPK6的激活,繼而伴隨對(duì)一些防衛(wèi)相關(guān)基因的強(qiáng)烈誘導(dǎo),如WRKY22、WRKY29及防御素PDF1.2。這種表達(dá)變化是否代表HSL誘導(dǎo)的抗性的一部分還需要進(jìn)一步驗(yàn)證[22]。
3 細(xì)菌AHLs對(duì)植物生長(zhǎng)發(fā)育的影響
目前另外一個(gè)關(guān)于植物和AHLs互作研究熱點(diǎn)是AHLs對(duì)植物生長(zhǎng)發(fā)育的影響。許多研究都表明不同的HSL處理后可引起根發(fā)育的變化(主要是擬南芥)。如前面所述,AHLs的差異主要在于脂肪鏈長(zhǎng)度的不同以及C3脂肪酸碳?xì)埢〈锏牟煌?。Ortiz-Castro等[31]通過(guò)測(cè)定不同濃度AHLs處理后擬南芥生長(zhǎng)的表型變化,發(fā)現(xiàn)AHLs主要影響主根的生長(zhǎng)、側(cè)根的形成和根毛的發(fā)育,其中C10-HSL是改變擬南芥根系統(tǒng)結(jié)構(gòu)最有效的AHLs。Von Rad等[25]研究表明擬南芥根經(jīng)1-10 μmol/L C4-和C6-HSL處理后可以提高根的生長(zhǎng),作者利用基因芯片技術(shù)檢測(cè)擬南芥對(duì)AHLs的響應(yīng),發(fā)現(xiàn)C6-HSL可以引起細(xì)胞生長(zhǎng)相關(guān)基因及生長(zhǎng)激素調(diào)控基因的表達(dá)。生長(zhǎng)素和細(xì)胞分裂素的比率增加,這也解釋了這種表型。在擬南芥中C6-HSL對(duì)主根生長(zhǎng)的刺激作用可能與鈣調(diào)素有關(guān),因?yàn)橥庠词┘? μmol/L的3OC6-HSL后,不管是轉(zhuǎn)錄水平還是蛋白水平都可以引起根部鈣調(diào)素表達(dá)的上升,而鈣調(diào)素缺失突變體對(duì)3OC6-HSL引起的主根延長(zhǎng)不敏感。另外,鈣調(diào)素并不參與長(zhǎng)鏈AHLs如C10-HSL及C12-HSL引起的對(duì)主根長(zhǎng)度的抑制作用,因此,植物響應(yīng)的特征依賴于HSL另一部分不同的結(jié)構(gòu)[32]。Jin等[33]研究發(fā)現(xiàn)在擬南芥中G-蛋白偶聯(lián)受體Cand2和Cand7參與調(diào)控細(xì)菌AHLs介導(dǎo)的根的伸長(zhǎng)。Mathesius等[34]利用蛋白組學(xué)的方法研究蒺藜苜蓿對(duì)細(xì)菌QS信號(hào)3OC12-HSL和3OC16-HSL的響應(yīng),發(fā)現(xiàn)150多種蛋白均發(fā)生了變化,大約有1/3的上調(diào)蛋白對(duì)各自的AHL是特異的。包括參與植物防衛(wèi)反應(yīng)、脅迫響應(yīng)、能量和代謝活性、轉(zhuǎn)錄加工、細(xì)胞骨架活性、激素響應(yīng)等功能調(diào)控的蛋白質(zhì)。近期Bai等[35]研究表明oxo-C10-HSL而不是它的非修飾同源物C10-HSL可以誘導(dǎo)綠豆植物不定根的形成,oxo-C10-HSL加速了向基的生長(zhǎng)素運(yùn)輸, 其中生長(zhǎng)素依賴的不定根的形成與過(guò)氧化氫以及NO依賴的cGMP信號(hào)轉(zhuǎn)導(dǎo)途徑密切相關(guān)。外源施加1 μmol/L的S. meliloti特異的3-oxo-C14-HSL可以顯著提高苜蓿根瘤的數(shù)目,但是對(duì)根長(zhǎng)和側(cè)根數(shù)目沒(méi)有影響,并且對(duì)根瘤數(shù)目的影響是通過(guò)依賴乙烯不依賴自動(dòng)調(diào)節(jié)的機(jī)制實(shí)現(xiàn)的[36]。
根據(jù)這些年對(duì)植物和AHLs互作的研究,總結(jié)了擬南芥對(duì)含有不同長(zhǎng)度側(cè)鏈的HSL分子的響應(yīng)。包括對(duì)植物抗性、主根延伸、次根形成、不定根形成及根毛生長(zhǎng)的影響(表1)[14,22,25,31,35]。
4 不同AHLs在植物體內(nèi)的運(yùn)輸及對(duì)系統(tǒng)反應(yīng)的誘導(dǎo)
目前關(guān)于AHLs的研究很關(guān)鍵的一個(gè)問(wèn)題是AHLs在植物體內(nèi)的運(yùn)輸是否是它們影響植物的前提條件。研究表明?;鶄?cè)鏈長(zhǎng)度小于C8的AHLs可以較快地進(jìn)入植物根部,然后運(yùn)輸?shù)角o。而側(cè)鏈長(zhǎng)度較長(zhǎng)(一般大于10)的AHLs在根表面附著,不能在大麥、玉米和擬南芥中運(yùn)輸[22,25,37]。因此,AHLs在植物體內(nèi)的轉(zhuǎn)運(yùn)能力和它對(duì)生長(zhǎng)促進(jìn)作用的相關(guān)性還是很難以捉摸的。
AHLs對(duì)植物影響的另一個(gè)方面是它對(duì)系統(tǒng)抗性的誘導(dǎo)。盡管oxo-C14-HSL不能在莖中被檢測(cè)到,但經(jīng)oxo-C14-HSL預(yù)處理后可以顯著提高葉子對(duì)活體病原菌的抗性[22]。因此,揭示AHLs誘導(dǎo)的植物體內(nèi)信號(hào)是理解AHLs影響宿主植物機(jī)制的關(guān)鍵一步。Schikora等[22]鑒定出MPK6是oxo-C14-HSL信號(hào)轉(zhuǎn)導(dǎo)途徑的關(guān)鍵激酶。Liu等[38]發(fā)現(xiàn)在擬南芥中GCR1 G蛋白以及典型的Gα亞基GAP1是C6-HSL信號(hào)轉(zhuǎn)導(dǎo)途徑必需的。
在植物中抗菌及抗蟲(chóng)間的相互作用是跨界交叉對(duì)話的另一個(gè)例子。在利用天蛾幼蟲(chóng)對(duì)煙草抗蟲(chóng)性測(cè)試中發(fā)現(xiàn)C6-HSL處理后的植株幼蟲(chóng)增加了4倍的生物量,作者通過(guò)對(duì)C6-AHL和茉莉酸誘導(dǎo)的脂肪酸-氨基酸結(jié)合物處理的植株進(jìn)行基因芯片分析,發(fā)現(xiàn)蛋白酶抑制劑下調(diào)表達(dá)。這個(gè)結(jié)果表明幼蟲(chóng)的生物量增加可能是由于C6-HSL對(duì)JA介導(dǎo)防衛(wèi)反應(yīng)的直接或間接作用導(dǎo)致的[39]。
5 總結(jié)與展望
AHLs介導(dǎo)的細(xì)菌QS系統(tǒng)不僅參與細(xì)菌多種生理行為和生物學(xué)功能的調(diào)控,還影響真核生物基因的表達(dá),反過(guò)來(lái)真核生物也可能會(huì)通過(guò)產(chǎn)生AHLs類似物影響細(xì)菌QS反應(yīng)[40-42]。最早是在從海洋紅藻中發(fā)現(xiàn)一種信號(hào)分子類似物-鹵化呋喃酮,它能干擾細(xì)菌的QS系統(tǒng),使之不能在其葉表群聚 (Swarming)和形成生物膜,現(xiàn)在已在豌豆、水稻、番茄、大豆和苜蓿等植物中發(fā)現(xiàn)可能存在細(xì)菌QS信號(hào)類似物,這些類似物可以破化或者促進(jìn)病原菌的QS系統(tǒng),但是目前這些植物化合物還沒(méi)有通過(guò)化學(xué)方法鑒定,所以它們與AHLs在結(jié)構(gòu)上的相似性還不是很清楚[29]。通過(guò)轉(zhuǎn)基因抑制AHLs合成基因的表達(dá),降低了細(xì)菌AHLs的產(chǎn)生,從而成功地降低它們的毒力[43-46]。另外,可以產(chǎn)生不同類型AHLs復(fù)合物的轉(zhuǎn)基因番茄,改變了植物促生細(xì)菌在根際的活力[47]。隨著科學(xué)的發(fā)展,一旦從高等植物中獲得信號(hào)分子阻遏物,就可以通過(guò)轉(zhuǎn)基因的方式達(dá)到抗病的目的,而不會(huì)擔(dān)心病原菌的抗性與生態(tài)安全性問(wèn)題。
植物相關(guān)細(xì)菌的QS系統(tǒng)調(diào)控與生物防治相關(guān)的表型包括調(diào)控抗生素和胞外酶的產(chǎn)生、生物膜形成和根際定殖能力等。將細(xì)菌的群體調(diào)控運(yùn)用到生防中可以有兩種策略,一種是針對(duì)病原細(xì)菌,通過(guò)利用一些低分子量化合物或AHLs降解酶干擾或淬滅QS信號(hào)分子AHLs,弱化病原菌致病力,控制發(fā)病的數(shù)量和蔓延程度,從而抑制病害發(fā)展[48-50];另一種是針對(duì)生防菌,通過(guò)分子生物學(xué)手段操縱QS信號(hào)途徑增強(qiáng)生防相關(guān)基因的表達(dá),從而更好地發(fā)揮生防菌的優(yōu)勢(shì)[51]。由于微生物與植物之間互作的復(fù)雜性,目前對(duì)生防細(xì)菌QS的探索還集中在對(duì)其調(diào)控機(jī)理的研究。人們對(duì)于QS信號(hào)參與調(diào)控植物促生及抗逆的分子機(jī)制,以及AHLs下游的信號(hào)傳導(dǎo)途徑等還缺乏了解。為了更好地開(kāi)發(fā)利用生防菌,揭示其AHLs跨界信號(hào)轉(zhuǎn)導(dǎo)參與調(diào)節(jié)寄主生長(zhǎng)發(fā)育和抗逆的機(jī)制是十分必要的。植物與細(xì)菌相互作用方式能否被運(yùn)用到生產(chǎn)實(shí)踐中來(lái),還有許多工作要做,對(duì)QS的進(jìn)一步研究有可能為控制作物病害及促進(jìn)植物生長(zhǎng)提供有效的生物技術(shù)。
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