劉羽 傳志 長生 翠 興軍
摘要:過敏性反應(yīng)是植物抗病機制中最常見的形式之一。過敏性誘導(dǎo)反應(yīng)(Hypersensitive-induced reaction)基因HIR是與過敏反應(yīng)相關(guān)的一類基因,屬于PID家族成員,參與許多細(xì)胞生理過程,并與細(xì)胞程序化死亡有密切關(guān)系。本研究從花生轉(zhuǎn)錄組文庫中篩選到編碼HIR基因的部分序列,通過5′-RACE獲得花生HIR基因的全長cDNA序列,并克隆了其基因組序列。分析表明,花生HIR基因與其他物種HIR基因具有高度同源性。對6個物種共17條HIR序列使用最大似然法進行進化分析表明,該基因在進化中受到了強烈的純化選擇作用。qRT-PCR分析發(fā)現(xiàn),該基因的表達量在冷處理4 h時顯著降低,隨著處理時間延長其表達量逐漸回升;在病菌處理的材料中該基因的表達下調(diào)。這些結(jié)果為進一步研究HIR基因在花生抗病、耐逆中的功能奠定了基礎(chǔ)。
關(guān)鍵詞:花生;HIR;基因表達;抗逆;抗?。患兓x擇
中圖分類號:Q785文獻標(biāo)識號:A文章編號:1001-4942(2014)05-0001-06
病菌侵染植物后會誘導(dǎo)相關(guān)基因的表達,引起物質(zhì)積累和代謝途徑的改變,進而使植物表現(xiàn)出一系列的生理反應(yīng)。植物依賴兩個免疫機制來對抗病原:病原物相關(guān)分子模式觸發(fā)的免疫(PAMP-triggered immunity, PTI)和效應(yīng)子觸發(fā)的免疫(Effector-triggered immunity, ETI)[1]。在PTI途徑中,植物基于病原體分子的進化保守性來提供基本的免疫力;在ETI途徑中,植物通過識別病原體的非毒性Avr基因產(chǎn)物,激活抗性基因,產(chǎn)生過敏反應(yīng)(HR),在細(xì)胞內(nèi)激活一系列反應(yīng),包括活性氧的產(chǎn)生、胞內(nèi)離子流的變化、細(xì)胞膜功能紊亂等[2,3]。HR反應(yīng)導(dǎo)致感染部位細(xì)胞迅速死亡從而阻止病原體的蔓延,HR蛋白通過誘導(dǎo)HR反應(yīng),在植物抗病性上起著重要作用[4]。
過敏性誘導(dǎo)反應(yīng)基因(HIR)是與HR反應(yīng)相關(guān)的一類基因,他們屬于PID(Proliferation, ion channel regulation, and death)家族成員,PID蛋白由防衛(wèi)反應(yīng)基因抑制素Prohibitins和Stomatins兩類蛋白組成。PID家族蛋白參與許多細(xì)胞生理過程,包括離子通道調(diào)節(jié)、細(xì)胞死亡等[5~8]。1998年,Karrer等[9]在煙草中最早鑒定出HIR基因,并證明該基因能夠在葉片中誘導(dǎo)PR2的表達,產(chǎn)生組織壞死,該基因被命名為NG1。隨后,Nadimpalli等[5]根據(jù)NG1氨基酸序列,在玉米中鑒定出Zm-HIR1、Zm-HIR2和Zm-HIR3三個基因。2003年,Rostoks等[10]在大麥中克隆到了Hv-HIR1、Hv-HIR2、Hv-HIR3和Hv-HIR4四個基因,其中Zm-HIR3和Hv-HIR3基因在模擬病原侵害自發(fā)壞死的突變體上出現(xiàn)了明顯的上調(diào)表達,證明HIR不僅在雙子葉植物中通過參與HR反應(yīng)誘導(dǎo)細(xì)胞死亡及抗病功能,在多種單子葉植物中同樣參與HR反應(yīng)。Jung等[11,13]將辣椒的CaHIR1和水稻的OsHIR1在擬南芥中過表達,引起了類似HR反應(yīng)的組織壞死,提高了對細(xì)菌及真菌的抗性,且證明CaHIR1在胡椒抵御滲透脅迫中也發(fā)揮了重要作用。Choi等[12]發(fā)現(xiàn)CaHIR1在植物抗病及免疫過程中是參與植物細(xì)胞死亡的正調(diào)節(jié)蛋白。HIR基因已從許多植物中克隆到,花生是我國重要的經(jīng)濟作物,目前,在花生上尚未見HIR基因克隆的報道。
1材料與方法
1.1材料與處理
本研究選用花生品種魯花14號,于光照培養(yǎng)箱中培養(yǎng),光照時間16 h,溫度28℃;黑暗8 h,溫度26℃。青枯病菌在含有紅四氮唑(TTC)的NA培養(yǎng)基中培養(yǎng),用無菌水懸浮菌液至OD600=0.6。使用Tseng等[14]的方法侵染兩周齡花生的根,以水處理為對照。侵染48 h后將根切下,液氮速凍后于-80℃保存?zhèn)溆?。選用兩周齡花生苗進行4℃低溫處理(處理6、12、24、48 h),對照材料在25℃條件下培養(yǎng),每日光照16 h,處理24 h后將葉片切下,液氮速凍后于-80℃保存?zhèn)溆谩?/p>
1.2試驗方法
1.2.1花生總RNA提取和cDNA合成總RNA提取使用改良的CTAB法。用Eppendorf Biophotometer Plus型核酸蛋白檢測儀檢測RNA濃度和純度,1%瓊脂糖凝膠電泳鑒定其完整性。cDNA的合成參考TaKaRa PrimeScriptTM 1st Strand cDNA Synthesis Kit 試劑盒說明進行。
1.2.2AhHIR全長cDNA克隆從本實驗室花生果針轉(zhuǎn)錄組數(shù)據(jù)中獲得一段長為656 bp的EST序列,BLAST分析表明,該序列與大豆HIR(JN083835.1)具有高度同源性,其開放閱讀框不完整,5′端缺失約450 bp。根據(jù)該序列設(shè)計5′-RACE引物TSP1和TSP2(表1),通過Clontech公司SMARTerTM RACE cDNA擴增試劑盒進行5′-RACE擴增,PCR程序為:第一輪:94℃ 30 s,72℃ 3 min,5個循環(huán);94℃ 30 s,70℃ 30 s,72℃ 3 min,5個循環(huán);94℃ 30 s,68℃ 30 s,72℃ 3 min,25個循環(huán);72℃ 5 min。以第一輪PCR 產(chǎn)物為模板進行第二輪PCR 擴增,PCR程序為:94℃ 5 min;94℃ 30 s,60℃ 30 s,72℃ 2 min,30個循環(huán);72℃ 5 min。分析測序結(jié)果后設(shè)計引物HIROF和HIROR(表1),以花生cDNA為模板克隆AhHIR的完整ORF序列。
1.2.3AhHIR基因組序列的克隆和測序分析取干凈新鮮花生種子約500 mg, 采用CTAB法提取并純化基因組DNA。利用引物HIROF和HIROR,擴增AhHIR的基因組序列,測序后與cDNA序列比對,驗證其是否為AhHIR的基因組序列。
1.2.4AhHIR的qRT-PCR分析qRT-PCR 反應(yīng)以花生根和葉不同脅迫處理的cDNA作模板,以花生Actin基因為內(nèi)參,以HIRQF和HIRQR為引物(表1),采用FastStart SYBR Green試劑盒(Roche)進行擴增。反應(yīng)程序為:預(yù)變性95℃ 10 min;兩步法擴增95℃ 15 s,60℃ 1 min,40個循環(huán);測定溶解曲線95℃ 15 s,60℃ 15 s, 95℃ 15 s。每個反應(yīng)均設(shè)3 次重復(fù)。根據(jù)溶解曲線檢測PCR產(chǎn)物的特異性。基因表達水平測定使用相對表達,通過2-△△CT方法計算。
1.2.5AhHIR的生物信息學(xué)分析AhHIR基因編碼蛋白預(yù)測使用EMBOSS Transeq(http://www.ebi.ac.uk/Tools/st/emboss_transeq/),跨膜區(qū)預(yù)測使用TMHMM (http://www.cbs.dtu.dk/services/TMHMM/)。使用NCBI在線工具BLAST和Phytozome下載與AhHIR同源的16條核酸和蛋白序列,用ClustalW軟件對其進行多序列比對,使用Mrbayes軟件進行進化樹構(gòu)建,用Evoview繪制進化樹,使用PAML軟件包進行適應(yīng)性進化分析,用Swiss-Model預(yù)測AhHIR蛋白三級結(jié)構(gòu)模型,使用PFAM數(shù)據(jù)庫檢驗預(yù)測模型,使用Swiss-PDBviewer標(biāo)記氨基酸位點。
1.2.6AhHIR的進化分析對與花生AhHIR同源的16條核酸序列,用ClustalW軟件進行核酸堿基序列對位排列,并對部分序列進行手動修正。使用MrBayes3.1.2軟件經(jīng)貝葉斯模型進行系統(tǒng)進化分析[21],模型中參數(shù)使用默認(rèn)值,共運行1 000 000代,每1 000代取樣一棵樹,去除前10 000代老化樣本,剩余樣本構(gòu)建最終進化樹。使用上述貝葉斯樹文件和序列重排文件作為輸入樣本,每條序列存在304個氨基酸位點,使用PAML軟件包內(nèi)的模型:M0、M1a、M2a、M3、M7和M8進行進化分析[22]。
2結(jié)果與分析
2.1AhHIR基因的克隆
RACE擴增結(jié)果見圖1A,經(jīng)測序、序列拼接后設(shè)計引物,擴增AhHIR的完整ORF及基因組序列,分別獲得了900 bp和1 900 bp的PCR產(chǎn)物(圖1B和圖1C),經(jīng)測序證明所克隆的序列均為花生HIR。該基因由5個外顯子和4個內(nèi)含子組成(圖2)。
2.2AhHIR的表達分析
qRT-PCR結(jié)果(圖3)表明,4℃處理6 h后,葉片中AhHIR表達出現(xiàn)明顯的下調(diào),表達水平只有對照的20%,但隨著處理時間的延長,AhHIR表達量逐漸升高,冷處理12 h后表達水平恢復(fù)到對照的47%,處理48 h后恢復(fù)到對照的76%。青枯病菌侵染48 h后根中AhHIR表達量下調(diào)約30%。
2.3AhHIR蛋白序列分析
用EMBOSS Transeq對AhHIR基因編碼的蛋白序列預(yù)測表明,該基因編碼288個氨基酸。將預(yù)測的花生HIR蛋白序列與其他5個物種的16條HIR蛋白序列使用ClustalW進行同源比對,發(fā)現(xiàn)不同物種間HIR同源性很高,達95%以上,其中花生與大豆和菜豆親緣關(guān)系最近。根據(jù)TMHMM預(yù)測結(jié)果,花生HIR蛋白存在跨膜區(qū)的概率小于0.1%,存在膜上的概率小于5%,推測該蛋白應(yīng)存在于胞質(zhì)中。該蛋白與其他同源蛋白相似,N端有一個十四酰化的甘氨酸,可將蛋白錨定到質(zhì)膜上[10]。
2.4AhHIR的系統(tǒng)進化分析
選用包括花生在內(nèi)的6個物種共17條HIR基因序列,根據(jù)貝葉斯模型構(gòu)建進化樹(圖4),結(jié)果顯示整個進化樹的枝長較短,這與HIR基因的高度保守有關(guān)。根據(jù)進化樹各枝遺傳距離,將其分為三種類型(在進化樹中分別以色塊和括號標(biāo)記),AhHIR與大豆HIR1、玉米HIR1、小麥HIR1和HIR2、大麥HIR1聚為類型A;大豆HIR4、玉米HIR4等屬于類型C,類型C的HIR基因與其他類型遺傳距離較遠(yuǎn)。查詢PFAM蛋白數(shù)據(jù)庫,發(fā)現(xiàn)類型C的HIR蛋白除了在N端存在與其他類型相同的Band-7結(jié)構(gòu)域,還在C端存在其他結(jié)構(gòu)域。
2.5選擇壓力和氨基酸替代情況分析
選用6個物種共17條HIR基因序列通過比對重排,每一條序列含有912個堿基位點,304個氨基酸位點,用PAML分析時選用的模型參數(shù)參見表2,似然率檢驗結(jié)果參見表2。根據(jù)M0模型,所有位點與分支的平均ω=0.05997,說明HIR基因在進化中受強烈的純化選擇。在M8模
大豆(G. max),NM_001289276.1;GmaHIR3:大豆(G. max),JN083834.1;GmaHIR3like: 大豆(G. max),NM_001252931.2;GmaHIR4: 大豆(G. max),JN083833.1;GmaHIR4like:大豆(G. max),NM_001254549.1;CanHIR:辣椒(Capsicum annuum)AY529867.1。
圖4不同物種HIR基因系統(tǒng)進化樹及對應(yīng)的蛋白結(jié)構(gòu)型BEB分析結(jié)果中,針對所有氨基酸位點的ω值進行統(tǒng)計,在99%后驗概率下,ω值≤0.1的為負(fù)選擇位點,共存在202個,占總序列的69%;ω≤0.01的負(fù)選擇位點有129個,占總數(shù)的44%。位點編號以HvuHIR1為標(biāo)準(zhǔn)(圖5)。蛋白晶體模型預(yù)測結(jié)果表明,AhHIR與同樣存在Band-7 domain的Stomatin蛋白三級結(jié)構(gòu)(圖6A)相同[20]。將以上位點數(shù)據(jù)通過SwissPDB-viewer導(dǎo)入AhHIR晶體模型中,結(jié)果顯示這些受強烈純化選擇的氨基酸位點大多位于α螺旋和β折疊中(圖6B、C),這部分氨基酸在維持蛋白結(jié)構(gòu)中非常重要,而通道區(qū)域(圖6B白色箭頭標(biāo)記)的保守性相對較低。
3討論
HIR基因參與ETI途徑的免疫應(yīng)答[5,10~12,18],在植物HR反應(yīng)中行使重要的功能。本研究首次在花生中克隆了HIR基因,對花生HIR氨基酸序列分析表明其存在Band-7蛋白結(jié)構(gòu)域,AhHIR蛋白可能與其他家族成員一樣參與了細(xì)胞膜離子通道的控制[5]。通過qRT-PCR分析了該基因在受到生物脅迫和非生物脅迫時的表達情況,結(jié)果表明,兩種逆境脅迫均使AhHIR表達短期下調(diào)。由于HIR的表達升高可能會導(dǎo)致更多的細(xì)胞死亡[11],短期內(nèi)的低溫脅迫使HIR基因強烈下調(diào)有助于細(xì)胞死亡率降低,隨著低溫脅迫延續(xù),HIR基因緩慢上調(diào),這可使細(xì)胞死亡正常化,但其表達量并沒有超出正常表達水平。HIR基因在逆境下的表達變化可能與細(xì)胞為適應(yīng)環(huán)境改變而做出的一系列生理反應(yīng)有關(guān),如誘使內(nèi)源激素合成信號的傳導(dǎo)以及活性氧的積累[19]。
生物在進化中對環(huán)境的改變會做出一系列的適應(yīng)性進化,例如核酸的突變和蛋白的變化,HIR基因在進化分析中表現(xiàn)為強烈的保守性,在99%后概率檢驗下,ω≤0.1的負(fù)選擇位點有202個,占總數(shù)的69%,ω≤0.01的負(fù)選擇位點有129個,占總數(shù)的44%,這說明HIR基因受到了強烈的純化選擇,可能是由于該基因的功能非常重要,該基因突變后植物難以存活。將這些高度保守位點導(dǎo)入Band-7 domain蛋白質(zhì)三級結(jié)構(gòu)模型發(fā)現(xiàn),大多數(shù)受強烈純化選擇的位點都位于α螺旋和β折疊中,而在3個Band-7亞基形成的通道結(jié)構(gòu)中的氨基酸位點保守性相對較低。
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[15]Tavernarakis N, Driscoll M, Kyrpides N C. The SPFH domain: implicated in regulating targeted protein turnover in stomatins and other membrane-associated proteins [J]. Trends in Biochemical Sciences, 1999, 24(11): 425-427.
[16]Browman D T, Hoegg M B, Robbins S M. The SPFH domain-containing proteins: more than lipid raft markers [J]. Trends in Cell Biology, 2007, 17(8): 394-402.
[17]Qi Y, Tsuda K, Nguyen L V, et al. Physical association of Arabidopsis hypersensitive induced reaction proteins (HIRs) with the immune receptor RPS2 [J]. Journal of Biological Chemistry, 2011, 286(36): 31297-31307.
[18]Zhou L, Cheung M Y, Li M W, et al. Rice hypersensitive induced reaction protein 1 (OsHIR1) associates with plasma membrane and triggers hypersensitive cell death[J]. BMC Plant Biology, 2010, 10(1): 290.
[19]Fujita M, Fujita Y, Noutoshi Y, et al. Crosstalk between abiotic and biotic stress responses: a current view from the points of convergence in the stress signaling networks [J]. Current Opinion in Plant Biology, 2006, 9(4): 436-442.
[20]Yokoyama H, Fujii S, Matsui I. Crystal structure of a core domain of stomatin from Pyrococcus horikoshii ill ustrates a novel trimeric and coiled-coil fold [J]. Journal of Molecular Biology, 2008, 376(3): 868-878.
[21]Yang Z. PAML: a program package for phylogenetic analysis by maximum likelihood [J]. Computer Applications in the Biosciences: CABIOS, 1997, 13(5): 555-556.
[22]Yang Z. Maximum likelihood estimation on large phylogenies and analysis of adaptive evolution in human influenza virus A [J]. Journal of Molecular Evolution, 2000, 51(5): 423-432.山 東 農(nóng) 業(yè) 科 學(xué)2014,46(5):7~11,30Shandong Agricultural Sciences
[12]Choi H W, Kim Y J, Hwang B K. The hypersensitive induced reaction and leucine-rich repeat proteins regulate plant cell death associated with disease and plant immunity [J]. Molecular Plant-Microbe Interactions, 2011, 24(1): 68-78.
[13]Jung H W, Lim C W, Lee S C, et al. Distinct roles of the pepper hypersensitive induced reaction protein gene CaHIR1 in disease and osmotic stress, as determined by comparative transcriptome and proteome analyses[J]. Planta, 2008, 227(2): 409-425.
[14]Tseng H, Katawczik M, Mila A. Comparison of Ralstonia solanacearum strains isolated from tobacco and vegetable crops in North Carolina[C]. The American Phytopathological Society, 2012, 102(7): 122.
[15]Tavernarakis N, Driscoll M, Kyrpides N C. The SPFH domain: implicated in regulating targeted protein turnover in stomatins and other membrane-associated proteins [J]. Trends in Biochemical Sciences, 1999, 24(11): 425-427.
[16]Browman D T, Hoegg M B, Robbins S M. The SPFH domain-containing proteins: more than lipid raft markers [J]. Trends in Cell Biology, 2007, 17(8): 394-402.
[17]Qi Y, Tsuda K, Nguyen L V, et al. Physical association of Arabidopsis hypersensitive induced reaction proteins (HIRs) with the immune receptor RPS2 [J]. Journal of Biological Chemistry, 2011, 286(36): 31297-31307.
[18]Zhou L, Cheung M Y, Li M W, et al. Rice hypersensitive induced reaction protein 1 (OsHIR1) associates with plasma membrane and triggers hypersensitive cell death[J]. BMC Plant Biology, 2010, 10(1): 290.
[19]Fujita M, Fujita Y, Noutoshi Y, et al. Crosstalk between abiotic and biotic stress responses: a current view from the points of convergence in the stress signaling networks [J]. Current Opinion in Plant Biology, 2006, 9(4): 436-442.
[20]Yokoyama H, Fujii S, Matsui I. Crystal structure of a core domain of stomatin from Pyrococcus horikoshii ill ustrates a novel trimeric and coiled-coil fold [J]. Journal of Molecular Biology, 2008, 376(3): 868-878.
[21]Yang Z. PAML: a program package for phylogenetic analysis by maximum likelihood [J]. Computer Applications in the Biosciences: CABIOS, 1997, 13(5): 555-556.
[22]Yang Z. Maximum likelihood estimation on large phylogenies and analysis of adaptive evolution in human influenza virus A [J]. Journal of Molecular Evolution, 2000, 51(5): 423-432.山 東 農(nóng) 業(yè) 科 學(xué)2014,46(5):7~11,30Shandong Agricultural Sciences
[12]Choi H W, Kim Y J, Hwang B K. The hypersensitive induced reaction and leucine-rich repeat proteins regulate plant cell death associated with disease and plant immunity [J]. Molecular Plant-Microbe Interactions, 2011, 24(1): 68-78.
[13]Jung H W, Lim C W, Lee S C, et al. Distinct roles of the pepper hypersensitive induced reaction protein gene CaHIR1 in disease and osmotic stress, as determined by comparative transcriptome and proteome analyses[J]. Planta, 2008, 227(2): 409-425.
[14]Tseng H, Katawczik M, Mila A. Comparison of Ralstonia solanacearum strains isolated from tobacco and vegetable crops in North Carolina[C]. The American Phytopathological Society, 2012, 102(7): 122.
[15]Tavernarakis N, Driscoll M, Kyrpides N C. The SPFH domain: implicated in regulating targeted protein turnover in stomatins and other membrane-associated proteins [J]. Trends in Biochemical Sciences, 1999, 24(11): 425-427.
[16]Browman D T, Hoegg M B, Robbins S M. The SPFH domain-containing proteins: more than lipid raft markers [J]. Trends in Cell Biology, 2007, 17(8): 394-402.
[17]Qi Y, Tsuda K, Nguyen L V, et al. Physical association of Arabidopsis hypersensitive induced reaction proteins (HIRs) with the immune receptor RPS2 [J]. Journal of Biological Chemistry, 2011, 286(36): 31297-31307.
[18]Zhou L, Cheung M Y, Li M W, et al. Rice hypersensitive induced reaction protein 1 (OsHIR1) associates with plasma membrane and triggers hypersensitive cell death[J]. BMC Plant Biology, 2010, 10(1): 290.
[19]Fujita M, Fujita Y, Noutoshi Y, et al. Crosstalk between abiotic and biotic stress responses: a current view from the points of convergence in the stress signaling networks [J]. Current Opinion in Plant Biology, 2006, 9(4): 436-442.
[20]Yokoyama H, Fujii S, Matsui I. Crystal structure of a core domain of stomatin from Pyrococcus horikoshii ill ustrates a novel trimeric and coiled-coil fold [J]. Journal of Molecular Biology, 2008, 376(3): 868-878.
[21]Yang Z. PAML: a program package for phylogenetic analysis by maximum likelihood [J]. Computer Applications in the Biosciences: CABIOS, 1997, 13(5): 555-556.
[22]Yang Z. Maximum likelihood estimation on large phylogenies and analysis of adaptive evolution in human influenza virus A [J]. Journal of Molecular Evolution, 2000, 51(5): 423-432.山 東 農(nóng) 業(yè) 科 學(xué)2014,46(5):7~11,30Shandong Agricultural Sciences