王景晨 ,陳信波
(1.湖南農(nóng)業(yè)大學(xué)作物基因工程湖南省重點(diǎn)實(shí)驗(yàn)室,湖南 長(zhǎng)沙 410128;2.湖南農(nóng)業(yè)大學(xué)生物科學(xué)技術(shù)學(xué)院,湖南 長(zhǎng)沙 410128)
近年來,氣候?yàn)?zāi)害的頻發(fā)給農(nóng)作物的生長(zhǎng)和產(chǎn)量帶來嚴(yán)重的危害[1]。利用基因工程手段對(duì)農(nóng)作物進(jìn)行改良,提高農(nóng)作物對(duì)災(zāi)害性氣候的抵抗能力保證糧食穩(wěn)產(chǎn)具有重要的意義。
當(dāng)植物受到外界的干旱、高溫等非生物脅迫時(shí),植物會(huì)通過一系列的信號(hào)傳遞激發(fā)轉(zhuǎn)錄因子。被激發(fā)的轉(zhuǎn)錄因子會(huì)與相應(yīng)的順式作用元件相結(jié)合啟動(dòng)特定基因的表達(dá),從而對(duì)非生物脅迫進(jìn)行應(yīng)答。至今,已研究的參與植物應(yīng)答非生物脅迫的轉(zhuǎn)錄因子主要有 AP2/EREBP、MYB、WRKY、bZIP 和HSFs,其中AP2/EREBP和MYB兩類轉(zhuǎn)錄因子近年來的研究成果較多。下面就5種與非生物脅迫相關(guān)的轉(zhuǎn)錄因子的特征、結(jié)構(gòu)、功能以及在抗逆性方面的研究進(jìn)展分別予以敘述。
AP2/EREBP家族中的亞族DREB(dehydration responsive element binding protein)轉(zhuǎn)錄因子與植物非生物脅迫密切相關(guān)。相對(duì)于其它亞族,DREB轉(zhuǎn)錄因子序列中只含有一個(gè)AP2/EREBP保守結(jié)構(gòu)域,該域一般由59個(gè)氨基酸組成,其中在N端和C端分別有YRG和RAYD兩個(gè)保守元件。目前在水稻、大豆、小麥、玉米等農(nóng)作物中都分離出了DREB類轉(zhuǎn)錄因子。對(duì)DREB類轉(zhuǎn)錄因子功能的研究表明,DREB轉(zhuǎn)錄因子在植物對(duì)非生物脅迫應(yīng)答過程中起著重要的調(diào)控作用。在植物受逆境脅迫后,DREB轉(zhuǎn)錄因子表達(dá)量會(huì)在短時(shí)間內(nèi)迅速增加,調(diào)控一系列下游逆境相關(guān)基因的表達(dá),從而提高植物的抗逆性。近年來,就植物中報(bào)道的與抗逆相關(guān)DREB轉(zhuǎn)錄因子以及它們?cè)诳鼓嬷械淖饔脷w納于表1。
MYB轉(zhuǎn)錄因子以其N端特有的MYB保守結(jié)構(gòu)域而得名,由一系列高度保守的氨基酸殘基和間隔序列組成。每個(gè)MYB結(jié)構(gòu)域折疊成螺旋-轉(zhuǎn)角-螺旋的空間結(jié)構(gòu),其中包含有3個(gè)色氨酸殘基,這3個(gè)殘基被18~19個(gè)氨基酸殘基隔開,具有疏水核心的作用[11]。MYB轉(zhuǎn)錄因子一般由三個(gè)保守的功能域組成:一個(gè)DNA結(jié)合結(jié)構(gòu)域,一個(gè)轉(zhuǎn)錄激活結(jié)構(gòu)域,以及一個(gè)不完全界定的負(fù)調(diào)節(jié)區(qū)[12]。MYB轉(zhuǎn)錄因子在植物中幾乎參與了發(fā)育和代謝的各個(gè)方面。Lee和Schiefelbein從擬南芥中分離出來一系列與根毛發(fā)育相關(guān)的基因如TTG、CPC、WER和GL2,并認(rèn)為其中兩個(gè)MYB類轉(zhuǎn)錄因子CPC蛋白和WER蛋白是決定根表皮細(xì)胞發(fā)育的關(guān)鍵基因[13]。擬南芥過量表達(dá)AtMYB24基因會(huì)導(dǎo)致植株矮小且花器官發(fā)育不良,花藥不開裂,花粉無活性[14]。MYB轉(zhuǎn)錄因子在植物應(yīng)答非生物脅迫方面也扮演了非常重要的角色。近年來,在植物中報(bào)道的與抗逆相關(guān)MYB轉(zhuǎn)錄因子歸納于表2。
表1 應(yīng)答植物非生物脅迫的DREB類轉(zhuǎn)錄因子
表2 應(yīng)答植物非生物脅迫的MYB類轉(zhuǎn)錄因子
WRKY類轉(zhuǎn)錄因子是植物中特有的轉(zhuǎn)錄因子家族,在植物中分布廣泛。目前在水稻、白薯、野燕麥、馬鈴薯等農(nóng)作物中都分離出了WRKY類轉(zhuǎn)錄因子[21]。WRKY轉(zhuǎn)錄因子共同的結(jié)構(gòu)特征是擁有一個(gè)高度保守的WRKYGQK七肽核心序列,稱為WRKY域。WRKY轉(zhuǎn)錄因子在植物中參與眾多代謝過程的調(diào)控,如植物損傷反應(yīng)、植物衰老反應(yīng)及植物發(fā)育,同時(shí)有研究指出,WRKY轉(zhuǎn)錄因子也參與植物對(duì)非生物脅迫的應(yīng)答反應(yīng)。Wu等通過基因表達(dá)譜分析,結(jié)果表明OsWRKY11可以誘導(dǎo)激活棉籽糖合成中的一些基因,而棉籽糖的積累對(duì)Os-WRKY11過量表達(dá)植株的耐旱起著重要作用[22]。擬南芥中,AtWRKY25的過量表達(dá)植株相對(duì)野生型植株有更強(qiáng)的高溫脅迫抗性[23]。Talanova等對(duì)小麥苗進(jìn)行4℃冷脅迫處理,發(fā)現(xiàn)WRKY轉(zhuǎn)錄因子在冷處理15 min后出現(xiàn)高表達(dá),說明WRKY轉(zhuǎn)錄因子參與了小麥對(duì)冷脅迫的應(yīng)答反應(yīng)[24]。
bZIP類轉(zhuǎn)錄因子非常保守,并且在植物中廣泛分布。目前,已在擬南芥基因組、豆科植物基因組、水稻基因組中發(fā)現(xiàn)了大量的bZIP轉(zhuǎn)錄因子。所有的植物bZIP轉(zhuǎn)錄因子都含有非常保守的與特異DNA序列相結(jié)合的堿性結(jié)構(gòu)域以及參與寡聚化作用的亮氨酸拉鏈區(qū)。一般根據(jù)植物bZIP轉(zhuǎn)錄因子的結(jié)構(gòu)特點(diǎn)和功能將其劃分為10個(gè)亞族:A、B、C、D、E、F、G、H、I、S 亞族,這些亞族在植物生長(zhǎng)過程中各自行使著重要的功能。Zou等發(fā)現(xiàn)水稻bZIP轉(zhuǎn)錄因子中A亞族基因的OsABI5基因在高鹽脅迫下表達(dá)量上調(diào),而在低溫和干旱條件下表達(dá)量下調(diào),說明其參與了水稻對(duì)非生物脅迫的應(yīng)答[25]。S亞族是擬南芥中最大的bZIP亞族,Sung等的研究表明,胡椒中的CAbZIP1轉(zhuǎn)錄因子在逆境脅迫應(yīng)答中起著調(diào)控作用[26]。Liao等將大豆基因GmbZIP44,GmbZIP62和GmbZIP78轉(zhuǎn)入擬南芥中,發(fā)現(xiàn)它們能夠提高植株對(duì)鹽和低溫脅迫的抗性[27]。
在熱脅迫逆境中,植物中的熱激蛋白(Heat shock protein,HSP)會(huì)在體內(nèi)迅速的積累,并以分子伴侶的形式幫助相關(guān)蛋白重新折疊、穩(wěn)定、組裝和降解,從而提高植物在高溫逆境下的生存能力。植物熱激蛋白在高溫脅迫中的表達(dá)受一類專門的熱激轉(zhuǎn)錄因子調(diào)控,即熱激轉(zhuǎn)錄因子(Heat stress transcription factors,HSFs)。一般根據(jù)N端結(jié)合域與寡聚域結(jié)構(gòu)之間螺旋的連接長(zhǎng)度以及HR-A/B之間插入的氨基酸殘基數(shù),將植物HSFs分成A、B、C三類成員。目前已在水稻、番茄、擬南芥等多種植物中克隆出HSFs基因,并發(fā)現(xiàn)它們能提高植物在非生物脅迫下的抗逆能力,但現(xiàn)階段主要研究都集中在熱激蛋白方面,而對(duì)HSFs在植物熱脅迫下的調(diào)控機(jī)制和網(wǎng)絡(luò)仍不明確。
上述研究成果說明,轉(zhuǎn)錄因子的過量表達(dá)能夠提高植物在非生物脅迫下的抗逆能力。轉(zhuǎn)錄因子基因過量的表達(dá)會(huì)影響下游一系列基因的表達(dá),相對(duì)于單基因的過量表達(dá)更能影響植物在非生物脅迫下的生長(zhǎng)和產(chǎn)量;有些轉(zhuǎn)錄因子不但參與植物對(duì)非生物脅迫的應(yīng)答,同時(shí)還直接承擔(dān)植物生長(zhǎng)發(fā)育中的信號(hào)因子,如水稻OsABI5在成熟的花粉中的高表達(dá)直接影響著作物產(chǎn)量[26]。對(duì)轉(zhuǎn)錄因子日益成熟的研究和利用,為農(nóng)作物在非生物脅迫下的生長(zhǎng)和產(chǎn)量提供了非常有利的理論依據(jù)。在氣候?yàn)?zāi)害威脅農(nóng)作物生產(chǎn)的今天,通過轉(zhuǎn)錄因子對(duì)農(nóng)作物進(jìn)行改良,從而維持糧食產(chǎn)量的穩(wěn)定有極其重要的意義。
[1]楊太明,陳金華.江淮之間夏季高溫?zé)岷?duì)水稻生長(zhǎng)的影響[J].安徽農(nóng)業(yè)科學(xué),2007,35(27):8530-8531.
[2]Zhang Y,Chen C,Jin X F,et al.Expression of a rice DREB1 gene,OsDREB1D,enhances cold and high-salt tolerance in transgenic Arabidopsis[J].BMB Reports,2009,31(8):486-492.
[3]Dubouzet J G,Sakuma Y,Ito Y,et al.OsDREB genes in rice,O-ryza sativa L,encode transcription activators that function in drought-,high-salt and cold-responsive gene expression[J].Plant Journal,2003,33(4):751-763.
[4]Wang Q,Guan Y,Wu Y,et al.Overexpression of a rice Os-DREB1F gene increases salt,drought,and low temperature tolerance in both Arabidopsis and rice[J].Plant Molecular Biology,2008,67(6):589-602.
[5]Chen M,Xu Z,Xia L,et al.Cold-induced modulation and functional analyses of the DRE-binding transcription factor gene,Gm-DREB3,in soybean(Glycine max L.)[J].Journal of Experimental Botany,2009,60(1):121-135.
[6]Oh S J,Kwon C W,Choi D W,et al.Expression of barley HvCBF4 enhances tolerance to abiotic stress in transgenic rice[J].Plant Biotechnology Journal,2007,5(5):646-656.
[7]Gao S Q,Chen M,Xia L Q,et al.A cotton(Gossypium hirsutum)DRE-binding transcription factor gene,GhDREB,confers enhanced tolerance to drought,high salt,and freezing stresses in transgenic wheat[J].Plant Cell Reports,2005,28(2):301-311.
[8]Shan D P,Huang J G,Yang Y T,et al.Cotton GhDREB1 increases plant tolerance to low temperature and is negatively regulated by gibberellic acid[J].New Phytologist,2007,176(1):70-81.
[9]Xu Z S,Ni Z Y,Li Z Y,et al.Isolation and functional characterization of HvDREB1 a gene encoding a dehydration-responsive element binding protein in Hordeum vulgare[J].Journal of Plant Research,2009,122(1):121-130.
[10]Matsukura S,Mizoi J,Yoshida D,et al.Comprehensive analysis of rice DREB2-type genes that encode transcription factors involved in the expression of abiotic stress-responsive genes[J].Molecular Genetics and Genomics,2010,283(2):185-196.
[11]Zhong R Q,Richardson E A,Ye Z H.The MYB46 transcription factor is a direct target of SND1 and regulates secondary wall biosynthesis in Arabidopsis[J].Plant Cell,2007,19 (9):2776-2792.
[12]Frampton J.MYB transcription factors:their role in growth,differentiation and disease[M].Dordrecht:Kluwer academic publishers,2004:6-8.
[13]Lee M M,Schiefelbein J.Cell pattern in the Arabidopsis root epidermis determined by lateral inhibition with feedback[J].Plant Cell,2002,14(3):611-618.
[14]Yang X Y,Li J G,Pei M,et al.Over-expression of a flower-specific transcription factor gene AtMYB24 causes aberrant anther development[J].Plant Cell,2007,26(2):219-228.
[15]Su C F,Wang Y C,Hsieh T H,et al.A Novel MYBS3-Dependent Pathway Confers Cold Tolerance in Rice[J].Plant Physiology,2010,153:145-158.
[16]Quan R D,Hu S J,Zhang Z L,et al.Over expression of an ERF transcription factor TSRF1 improves rice drought tolerance[J].Plant Biotechnology Journal,2010,(8):476-488.
[17]Pil J S,Xiang F N,Qiao M,et al.The MYB96 Transcription Factor Mediates Abscisic Acid Signaling during Drought Stress Response In Arabidopsis[J].Plant Physiology,2009,151:275-289.
[18]Liao Y,Zou H F,Wang H W,et al.Soybean GmMYB76,Gm-MYB92 and GmMYB177 genes confer stress tolerance in transgenic Arabidopsis plants[J].Cell Research,2008,18:1047-1060.
[19]Gao J J,Zhang Z,Peng R H,et al.Forced expression of Mdmyb10,a myb transcription factor gene from apple,enhances tolerance to osmotic stress in transgenic Arabidopsis[J].Mol Biol publishers,2010,38(1):205-211.
[20]Devaiah B N,Madhuvanthi R,Karthikeyan A S,et al.Phosphate Starvation Responses and Gibberellic Acid Biosynthesis Are Regulated by the MYB62 Transcription Factor in Arabidopsis[J].Molecular Plant,2009,(2):43-58.
[21]Eulgem T,Somssich I E.Network s of WRKY transcription factors in defense signaling[J].Current Opinion in Plant Biology,2007,(10):366-371.
[22]Wu X,Shiroto Y,Kishitanis S,et al.Enhanced heat and drought tolerance in transgenicriceseedlingsoverexpressingOs-WRKY11 under the control of HSP101 promoter[J].Plant Cell Rep,2009,28:21-30.
[23]Li S,F(xiàn)u Q,Huang W,et a1.Functional analysis of an Arabidopsis transcription factor WRKY25 in heat stress[J].Plant Cell Rep,2009,28(4):683-693.
[24]Talanova V V,Titov A F,Topchieca L V,et al.Expression of WRKY transcription factor and stress protein genes in wheat plants during cold hardening and ABA treatment[J].Russian Journal of Plant Physiology,2009,56(5):702-708.
[25]Zou M,Guan Y,Ren H,et al.A bZIP transcription factor,Os-ABI5,is involved in rice fertility and st ress tolerance[J].Plant Molecular Biolog,2008,66:675-683.
[26]Sung C L,Hyong W C,In S H,et al.Functional roles of the pepper pathogen-induced bZIP transcription factor,CAbZIP1,in enhanced resistance to pathogen infection and environmental stresses[J].Planta,2006,224:1209-1225.
[27]Liao Y,Zou H F ,Wei W,et al.Soybean GmbZIP44,GmbZIP62 and GmbZIP78 genes functionas negative regulator of ABA signaling and confer salt and freezing tolerance in transgenic Arabidopsis[J].Planta,2008,228:225-240.