賀 振, 陳春峰, 張志想, 李世訪*

(1. 揚(yáng)州大學(xué)園藝與植物保護(hù)學(xué)院, 揚(yáng)州 225009; 2. 中國農(nóng)業(yè)科學(xué)院植物保護(hù)研究所,植物病蟲害生物學(xué)國家重點(diǎn)實驗室, 北京 100193)

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Reviews

馬鈴薯Y病毒科分子進(jìn)化研究進(jìn)展

賀 振1,2, 陳春峰1, 張志想2, 李世訪2*

(1. 揚(yáng)州大學(xué)園藝與植物保護(hù)學(xué)院, 揚(yáng)州 225009; 2. 中國農(nóng)業(yè)科學(xué)院植物保護(hù)研究所,植物病蟲害生物學(xué)國家重點(diǎn)實驗室, 北京 100193)

馬鈴薯Y病毒科Potyviridae包括許多重要的植物病毒。本文綜述了近年來該科馬鈴薯Y病毒屬Potyvirus、甘薯病毒屬Ipomovirus和禾草病毒屬Poacevirus內(nèi)20余種病毒的分子進(jìn)化研究現(xiàn)狀,從突變、重組、漂移、選擇和遷移5個方面探討了影響該科一些病毒分子進(jìn)化的因素,并展望了未來的研究方向,以期為該科病毒的有效防控提供理論依據(jù)。

馬鈴薯Y病毒科; 分子進(jìn)化

馬鈴薯Y病毒科Potyviridae是僅次于雙生病毒科的第二大植物病毒科[1]。根據(jù)2014年ICTV修訂的分類系統(tǒng),該科包括8個屬,分別為黑莓Y病毒屬Brambyvirus、大麥黃花葉病毒屬Bymovirus、甘薯病毒屬Ipomovirus、柘橙病毒屬M(fèi)acluravirus、禾草病毒屬Poacevirus、馬鈴薯Y病毒屬Potyvirus、黑麥草花葉病毒屬Rymovirus和小麥花葉病毒屬Tritimovirus,共計190個確定種和暫定種[1]。馬鈴薯Y病毒科病毒(potyvirids)大多寄主范圍廣泛,常給農(nóng)業(yè)生產(chǎn)帶來嚴(yán)重危害。該科病毒粒體呈線狀,直徑約為11～15 nm;大部分potyvirids具有一個長約為650～950 nm的單分體基因組,僅bymoviruses例外,其具有雙分體基因組,長度分別約為200～300 nm和500～600 nm。該科病毒基因組具有一個正單鏈RNA(positive-sense single-stranded RNA,+ssRNA)分子。單分體病毒大小約為8.0～11 kb;雙分體病毒基因組大小分別約為7.5 kb和3.5 kb。通常,單分體potyvirids可經(jīng)蚜蟲、螨類和粉虱等介體傳播,雙分體的bymoviruses可通過真菌(禾谷多黏菌Polymyxagraminis)傳播。此外,除bymoviruses外,大部分potyvirids可通過汁液摩擦傳播,部分potyviruses還可以通過種子傳播。

生物進(jìn)化是生命科學(xué)研究的最基本問題之一。分子進(jìn)化是指生物進(jìn)化過程中生物大分子的演變現(xiàn)象。分子系統(tǒng)樹是分子進(jìn)化研究的核心領(lǐng)域。自1859年達(dá)爾文在其《物種起源》中描述了第一個表示物種進(jìn)化關(guān)系的“樹”(分支圖解,branching diagram)以來,系統(tǒng)樹已經(jīng)廣泛應(yīng)用到生物分類與進(jìn)化起源的研究中。110年后,植物病毒研究中最早的一個基于核酸的分子系統(tǒng)樹由澳大利亞植物病毒學(xué)家Gibbs構(gòu)建發(fā)表[2]。其后由于測序技術(shù)的限制,以核酸信息為依據(jù)的系統(tǒng)樹分析在植物病毒研究領(lǐng)域進(jìn)展緩慢。自20世紀(jì)90年代以來,隨著測序技術(shù)的發(fā)展,大量的植物病毒基因組序列測定完成,基于植物病毒核酸信息的分子進(jìn)化研究得到快速發(fā)展。本文綜述了近20年來,20余種potyvirids的分子進(jìn)化研究現(xiàn)狀,以期加深對potyvirids種群結(jié)構(gòu)與進(jìn)化策略的理解,為設(shè)計合理的potyvirids病害防治策略提供依據(jù)。

1 馬鈴薯Y病毒屬Potyvirus

1.1 馬鈴薯Y病毒PotatovirusY(PVY)

PVY寄主范圍廣泛,常在馬鈴薯、煙草、番茄、辣椒和茄子等作物上造成嚴(yán)重的危害。依據(jù)生物學(xué)、血清學(xué)和基因組等特征,PVY包含3個基本株系,分別為:PVYN、PVYO和PVYC[3-4]。另外,近年來還報道了一些由重組產(chǎn)生的PVY新株系,例如PVYNTN和PVYNW等[5]。PVY基因組由長約9.7 kb的正單鏈RNA分子組成,包含一個大的開放閱讀框(open reading frame, ORF),編碼一個多聚蛋白(polyprotein),而后通過蛋白酶水解成P1、HC-Pro、P3等10個成熟的蛋白質(zhì)。另外,在P3蛋白N端編碼區(qū),還以+2移碼的方式翻譯出一個P3N-PIPO蛋白。在PVY編碼的上述11個蛋白中,Moury等發(fā)現(xiàn)在6K2和CP蛋白編碼區(qū)重組存在正向選擇位點(diǎn)[3];Cuevas等進(jìn)一步證明盡管PVY基因組中P1、P3、6K1、CI、Vpg、NIb和CP編碼區(qū)受到較強(qiáng)的負(fù)選擇壓力作用,但是部分堿基位點(diǎn)仍具有較強(qiáng)的正向選擇作用,而HC-Pro和NIa-Pro編碼區(qū)則未發(fā)現(xiàn)正向選擇位點(diǎn)[6-7];高芳鑾等發(fā)現(xiàn)P3N-PIPO具有較強(qiáng)的保守性,以中性進(jìn)化選擇為主,但也發(fā)現(xiàn)了一個正向選擇位點(diǎn)[8]。不同蛋白編碼區(qū)的選擇壓力結(jié)果證明,PVY的進(jìn)化過程受到強(qiáng)烈的負(fù)選擇、聯(lián)合中性選擇和部分位點(diǎn)的正選擇的共同作用。

PVY基因組間存在頻繁的重組現(xiàn)象。Ogawa等發(fā)現(xiàn)63%(32/51)已報道的PVY全長分離物屬于重組體,且重組位點(diǎn)多樣,不同蛋白編碼區(qū)重組位點(diǎn)發(fā)生頻率不一致,P1和CP蛋白編碼區(qū)重組發(fā)生頻率較高,組系間、組系內(nèi)皆有發(fā)生[9-10];Cuevas等的研究證明,截至2012年75%(58/77)已報道的PVY全長基因組具有不同的重組現(xiàn)象[7]。與已報道的3個基本株系相仿,PVY在系統(tǒng)發(fā)生分析上形成3個主要分支N、O和C,不同分支又分別可劃分為不同的亞組[9-10]。PVY不同組、亞組與其來源和寄主相關(guān),體現(xiàn)了地理(空間分布)和寄主對PVY進(jìn)化的限制作用[6,11]。PVY寄主種類還可能直接決定了P3N-PIPO的長度[7]。PVY具有比較明顯的種群分化,N組系中,PVY歐洲、北美和日本種群具有明顯的遺傳差距,部分亞種群的PVY具有典型的種群擴(kuò)張?zhí)卣鱗10]。

1.2 蕪菁花葉病毒Turnipmosaicvirus(TuMV)

TuMV廣泛分布在世界各地區(qū)的蘿卜、白菜、蕪菁等十字花科作物上,是除黃瓜花葉病毒Cucumbermosaicvirus(CMV)外,給世界各國蔬菜生產(chǎn)帶來嚴(yán)重?fù)p失的主要病毒[12-13]。TuMV寄主范圍廣泛,能夠侵染十字花科中大部分園藝作物。在東亞地區(qū),TuMV嚴(yán)重危害蕓薹屬作物的生產(chǎn)[14]。TuMV通過蚜蟲以非持久方式傳播[14]。根據(jù)TuMV侵染蕓薹屬Brassica和蘿卜屬Raphanus植物后表現(xiàn)癥狀的不同,TuMV可分為三種寄主類型:即只能侵染蕓薹屬植物并產(chǎn)生癥狀的B型[15];能夠同時侵染蕓薹屬植物和蘿卜屬植物,并都能引起癥狀的BR型;同時侵染蕓薹屬植物和蘿卜屬植物,只能在蕓薹屬植物上引起癥狀的B(R)型[16]。在中國、日本、越南等東亞、東南亞國家蘿卜上發(fā)生的TuMV絕大部分屬于BR型;在中國、澳大利亞和新西蘭蕓薹屬植物上發(fā)生的TuMV大部分屬于B型,而日本蕓薹屬植物上發(fā)生的TuMV主要為BR型[16-18]。

TuMV基因組中存在頻繁的重組現(xiàn)象,組系間或者組系內(nèi)的重組具有多種模型,不同地區(qū)的重組模型有差異,重組位點(diǎn)多發(fā)生在P1、P3和HC-Pro等蛋白編碼區(qū)[15-23]。2013年,Nguyen等對155個TuMV基因組序列進(jìn)行重組分析,結(jié)果發(fā)現(xiàn)多達(dá)118個TuMV分離物有重組現(xiàn)象[18-19]。另外,不同的重組模式還與病毒流行過程或者病毒的新發(fā)生相關(guān)。例如,在TuMV越南分離物中,大部分的重組位點(diǎn)在TuMV中國或者日本分離物中并未發(fā)現(xiàn),這說明TuMV在越南經(jīng)歷了一個獨(dú)特的進(jìn)化過程,可能是由于“建立者效應(yīng)”(founder effect)而導(dǎo)致的結(jié)果[18];在TuMV澳大利亞和新西蘭分離物中,發(fā)現(xiàn)21個重組位點(diǎn)與之前報道的不同,亦具有典型的地域特征[17]。

依據(jù)基因組全序列或者不同蛋白編碼區(qū)序列,對TuMV系統(tǒng)發(fā)育分析表明,歐亞大陸范圍內(nèi)不同TuMV分離物,結(jié)合其地理位置、寄主反應(yīng)類型的不同,可劃分為basal-B、Asia-BR、basal-BR和world B 4個分組[14, 23]。在種群流行時間的角度上,world B是當(dāng)前流行于世界大部分地區(qū)的TuMV主流株系,而basal-B則為TuMV的古老株系;Asia-BR和basal-BR兩個分組在一些地區(qū)時有發(fā)生,但并不占據(jù)主流地位[16-17,19]。2013年,Nguyen等在德國蘭花中發(fā)現(xiàn)了TuMV的祖先類型株系,該種類型在整個基因組上與TuMV當(dāng)前分離株親緣關(guān)系最近;其他諸如基因組長度、各蛋白編碼區(qū)長度,尤其是P1和CP區(qū)、蛋白酶切位點(diǎn)等方面,這些株系都表現(xiàn)出與TuMV最近的、最相似的特征,因此,這幾個病毒分離物被認(rèn)為是TuMV的祖先株系,并命名為TuMV-OM分組(即Orchis group)[19]。

利用貝葉斯法對TuMV的基因進(jìn)行分析,結(jié)果發(fā)現(xiàn)TuMV的三個主要蛋白編碼區(qū)核苷酸的替代率分別為:HC-Pro 1.11×10-3、P3 1.11×10-3和NIb 0.78×10-3核苷酸替代/位點(diǎn)/年(subs/site/year)[17,19]。進(jìn)化時間分析結(jié)果表明,TuMV-OM和TuMV-BIs(brassica-infecting TuMVs)組間約在1 005年前分化,而在TuMV BIs中,約850年前開始形成目前的4個分組[19]。

1.3 西葫蘆黃花葉病毒Zucchiniyellowmosaicvirus(ZYMV)

ZYMV是葫蘆科作物上的一類重要的病毒病原,目前已經(jīng)在世界上50多個國家發(fā)生[24]。ZYMV能夠引起葉片黃化、變形,植株矮化,果實褪色變形,嚴(yán)重降低作物產(chǎn)量[25]。ZYMV通過蚜蟲以非持久方式傳播,目前已鑒定出10種蚜蟲可在自然條件下傳播ZYMV,另有部分種類蚜蟲可在實驗室條件下傳播[26]。

ZYMV CP蛋白編碼區(qū)的核苷酸替代率為5.0×10-4核苷酸替代/位點(diǎn)/年[27]。Simmons等發(fā)現(xiàn)人類活動對ZYMV的分布具有重要影響,不同國家間ZYMV種群進(jìn)化受建立者效應(yīng)的影響較大[27]。在單一寄主中,ZYMV CP基因多樣性程度與一些動物RNA病毒相仿,為0.02%左右,CP基因中產(chǎn)生的突變也具有短暫、有害及快速被凈化的特點(diǎn)。蚜傳ZYMV病毒種群中還發(fā)現(xiàn)了一個證明存在缺失基因組短期互補(bǔ)作用的亞組系[28]。蚜傳和機(jī)械傳播對ZYMV種群突變的影響類似,但蚜傳對某些位點(diǎn)的突變有選擇性優(yōu)勢[29]。瓶頸作用影響ZYMV在單個西葫蘆植株中的系統(tǒng)傳播過程[30]。

1.4 大豆花葉病毒Soybeanmosaicvirus(SMV)

SMV在世界各大豆栽培產(chǎn)區(qū)普遍發(fā)生,常引起花葉、壞死等癥狀,顯著降低大豆產(chǎn)量和品質(zhì)[31]。依據(jù)不同品種大豆對SMV致病反應(yīng)的差異,SMV可分為多種株系。在美國,98個SMV分離物通過8個品種的大豆致病反應(yīng)分為7個株系(G1～G7)[32];依據(jù)該系統(tǒng),在韓國又發(fā)現(xiàn)了G5H、G6H和G7H株系[33-35];而在中國和日本,則分別采取了不同的株系分類系統(tǒng),例如中國把SMV劃分為21個株系[36-37],而日本則劃分為A～E共5個株系[38]。然而,Seo等發(fā)現(xiàn),SMV東北亞(韓國)種群和北美種群并不存在明顯的遺傳差異[39]。此外,Seo等還發(fā)現(xiàn)流行于韓國的SMV高侵染性株系多是重組體,重組對SMV跨越抗SMV大豆的屏障起到?jīng)Q定作用,并且發(fā)現(xiàn)SMV CI基因可能作為一個致病性決定因子,與大豆植株中抗SMV的Rsv3基因存在互作關(guān)系[39]。與之相似,Zhou等也發(fā)現(xiàn)SMV中存在普遍的重組現(xiàn)象[40],證明SMV中國種群與韓國和美國種群間存在比較明顯的遺傳差異,SMV的部分基因處在比較強(qiáng)的正向選擇壓力中,例如P1、HC-Pro和P3[40]。

1.5 甘蔗花葉病毒Sugarcanemosaicvirus(SCMV)

SCMV是Potyvirus中重要的植物病原,在世界范圍內(nèi)廣泛侵染玉米、甘蔗、高粱等禾本科作物和雜草,常造成嚴(yán)重的經(jīng)濟(jì)損失[41-42]。Li等和Xie等發(fā)現(xiàn),SCMV分離物存在兩個分組,組間具有較為清晰的寄主和地理特異性,不同來源的SCMV種群存在一定的基因交流現(xiàn)象;重組在SCMV基因組中發(fā)生的頻率較高[43-44]。SCMV處于較強(qiáng)的負(fù)選擇壓力作用下,近CP基因部分位點(diǎn)表現(xiàn)出較強(qiáng)的多樣性選擇作用[43]。

1.6 甘薯羽狀斑駁病毒Sweetpotatofeatherymottlevirus(SPFMV)

SPFMV是甘薯上最重要的病毒病原之一[45]。其在世界范圍內(nèi)分布廣泛,常造成儲藏期甘薯產(chǎn)生黃褐色龜裂和表皮變色[45]。目前,已報道的SPFMV包含4個株系,分別為RC(russet crack)、O(ordinary)、C(common)和EA(East Africa)[45-46]。RC、O和C株系分布廣泛,而EA株系主要分布在東非的部分地區(qū)[47]。SPFMV不同株系間存在一定程度的重組現(xiàn)象[47-48],Tugume等發(fā)現(xiàn)6K2-Vpg-NIaPro區(qū)是SPFMV-EA株系基因組上的一個重組熱點(diǎn)區(qū)域(recombination hotspot)[47]。在東非,SPFMV野生寄主種群與甘薯種群間存在較為明晰的跨寄主間傳播;相較于C株系,EA株系在東非具有很高的遺傳多樣性,可能起源于該地區(qū)[47]。

1.7 李痘病毒Plumpoxvirus(PPV)

PPV是李屬作物上的重要病原,由蚜蟲傳播,在世界范圍內(nèi)廣泛分布,常給李子等核果類果樹造成毀滅性災(zāi)害[49]。PPV具有多種不同株系,目前分布較為廣泛的主要包括PPV-D、M和Rec3種[50],不同株系間存在頻率較高的重組現(xiàn)象[51-52]。Jridi等在實驗室無介體昆蟲條件下,分析了PPV-M單一侵染桃樹15年后PPV種群結(jié)構(gòu)的變化,結(jié)果發(fā)現(xiàn),PPV可在單一寄主中建立寄主內(nèi)多樣性種群[53]。而在田間條件下,Predajňa等發(fā)現(xiàn)共侵染PPV-D、M和Rec3種株系,7年后,PPV-D和Rec兩種株系消失,而PPV-M株系產(chǎn)生大量的單體型變體,但并沒有產(chǎn)生明顯的遺傳差異[52]。依據(jù)CP基因,Gibbs等發(fā)現(xiàn)PPV-M株系的進(jìn)化率約1.4×10-4核苷酸替代/位點(diǎn)/年[54],與PVY、TuMV等其他馬鈴薯Y病毒屬成員相似。

1.8 玉米矮花葉病毒Maizedwarfmosaicvirus(MDMV)

MDMV世界性分布,是玉米上的一類重要的病毒病原。2012年,Achon等依據(jù)P1-HC-Pro基因,對西班牙MDMV種群分析發(fā)現(xiàn),MDMV P1和HC-Pro基因處在很強(qiáng)的純化選擇作用下,存在很高的遺傳多樣性,且P1的多樣性程度高于HC-Pro基因;系統(tǒng)發(fā)生分析發(fā)現(xiàn),MDMV具有5個分組,組內(nèi)存在明顯的重組現(xiàn)象,是MDMV種群多樣性的重要驅(qū)動力;相對于進(jìn)化時間和寄主因素,MDMV不同種群受到空間分布的影響較重[55]。

1.9 西瓜花葉病毒W(wǎng)atermelonmosaicvirus(WMV)

WMV是瓜類作物上一類重要的病毒病原之一。該病毒主要由蚜蟲傳播,常引起葫蘆科作物表現(xiàn)花葉癥狀[56]。Moreno等發(fā)現(xiàn),相對于CI和CP基因,WMV P1基因具有更高程度的遺傳多樣性;在CI-CP基因區(qū)段發(fā)現(xiàn)有重組現(xiàn)象,而在P1、CI和CP基因中并未發(fā)現(xiàn)重組位點(diǎn),表明單一重組基因受到強(qiáng)烈的負(fù)選擇作用影響;WMV種群進(jìn)化受到突變、重組和負(fù)選擇作用的驅(qū)動[57]。

1.10 哈登伯屬花葉病毒Hardenbergiamosaicvirus(HarMV)

HarMV是近年在澳大利亞西南部植物區(qū)流行的本土哈登伯豆Hardenbergiacomptoniana上發(fā)現(xiàn)的一種新的馬鈴薯Y病毒屬病毒[58-59]。Kehoe等于2014年首次發(fā)現(xiàn)在澳大利亞西南部地區(qū)HarMV從本土哈登伯豆傳播到入侵生物羽扇豆屬植物L(fēng)upinusspp.中,且HarMV基因組中存在重組現(xiàn)象[60]。

1.11 煙草脈帶花葉病毒Tobaccoveinbandingmosaicvirus(TVBMV)

TVBMV曾給北美和我國臺灣地區(qū)煙草生產(chǎn)帶來嚴(yán)重威脅,近年來在中國大陸多個省份煙草栽培區(qū)都有流行發(fā)生[61-62]。Zhang等通過對TVBMV的HC-Pro、P3、6K1和CP共4個基因的遺傳分析發(fā)現(xiàn),TVBMV中國分離物可形成MC和YN兩個分組,組間不存在明顯的基因交流;重組在TVBMV基因組中發(fā)生普遍;TVBMV受到較強(qiáng)的負(fù)選擇壓力作用,其中HC-Pro基因在這4個基因中受到的選擇壓力最大[63]。

1.12 薯芋花葉病毒Yammosaicvirus(YMV)

YMV是薯蕷Dioscoreasp.上一類危害嚴(yán)重的病毒病原,目前已在世界各地薯蕷產(chǎn)區(qū)廣泛流行發(fā)生[64]。依據(jù)NIb-CP-3UTR基因組區(qū),Bousalem等發(fā)現(xiàn)YMV具有極高的遺傳多樣性,共包含9個分組,且組間具有一定的地理相關(guān)性;YMV基因組中具有多種重組位點(diǎn),重組對YMV進(jìn)化具有重要的影響[65]。

1.13 番木瓜環(huán)斑病毒Papayaringspotvirus(PRSV)

PRSV是番木瓜和葫蘆科作物上的一類重要的病毒病原,是限制世界各地區(qū)番木瓜產(chǎn)量的主要因素之一[66]。PRSV主要包含兩種生物型:PRSV-P和PRSV-W。PRSV-P首次發(fā)現(xiàn)于美國夏威夷地區(qū),能夠自然侵染番木瓜,可給番木瓜生產(chǎn)帶來毀滅性危害,在世界各地廣泛流行[66];PRSV-W能夠自然侵染葫蘆科作物,但其流行分布報道得較少[12]。Bateson等證明PRSV-P可能是由PRSV-W型部分堿基突變產(chǎn)生[67]。PRSV的CP基因具有較高的遺傳多樣性,但不同地區(qū)遺傳多樣性程度不同,其中多樣性程度最高的是印度次大陸,說明PRSV很可能起源于東南亞地區(qū)并經(jīng)歷了長期的進(jìn)化過程[68]。

1.14 東亞西番蓮病毒EastAsianPassifloravirus(EAPV)

EAPV是西番蓮果實上重要的病毒病原之一,能夠引起西番蓮木質(zhì)病(woodiness disease),最初僅在日本和我國臺灣地區(qū)有過報道,目前已經(jīng)擴(kuò)展到馬來西亞和烏干達(dá)等地[69-71]。依據(jù)生物學(xué)和遺傳性狀,EAPV具有AO和IB兩種株系[69]。Fukumoto等發(fā)現(xiàn)在日本鹿兒島地區(qū)的EAPV僅存在AO株系,且具有很高的遺傳相似性;而在日本Sumiyo,EAPV表現(xiàn)為一個新出現(xiàn)病毒種群特征[72]。

1.15 菜豆普通花葉病毒Beancommonmosaicvirus(BCMV)

BCMV廣泛侵染多種豆科植物,常在菜豆Phaseolusvulgaris上引起嚴(yán)重危害,但在大豆上零星發(fā)生[73]。BCMV包括多種株系類型,例如NL1、NL4、NL6、NL7、PR1、RU1和US1-US10等[74]。Zhou等發(fā)現(xiàn)BCMV具有較高的寄主特異性,大豆分離物和花生分離物分別聚成獨(dú)立的分支;P1、P3、6K2和CP基因的N端具有較高的遺傳多樣性,且P1和P3中的部分堿基處于正選擇壓力作用下;重組在BCMV基因組中發(fā)生的頻率較高,是BCMV進(jìn)化過程中的重要作用力[75]。

1.16 辣椒脈斑駁病毒Chilliveinalmottlevirus(ChiVMV)

ChiVMV主要危害辣椒,能夠侵染茄科的多種作物,目前在東亞地區(qū)廣泛流行發(fā)生[76-78]。依據(jù)血清學(xué)、遺傳性狀和致病型等特征,ChiVMV表現(xiàn)出較高的多樣性[79-80],其不同種群受到空間分布的影響顯著[80]。ChiVMV的CP基因受到較強(qiáng)的純化選擇壓力,并伴有重組現(xiàn)象發(fā)生[80]。

2 甘薯病毒屬Ipomovirus

2.1 甘薯輕型斑駁病毒Sweetpotatomildmottlevirus(SPMMV)

SPMMV寄主范圍廣泛,自然條件下可侵染十幾個科的植物,是甘薯上重要的病毒病原之一[81-83]。SPMMV具有較高的遺傳多樣性,來自烏干達(dá)野生寄主的SPMMV在聚類分析中形成單獨(dú)的分支,與甘薯分離物具有明顯的遺傳差異[81, 84]。其P1基因的N端部分堿基處于較強(qiáng)的正向選擇壓力下,而HC-Pro、P3、6K1和CP等基因受到負(fù)選擇壓力影響顯著。SPMMV基因組中重組發(fā)生的頻率較高,特別是位于基因組兩端的區(qū)域重組位點(diǎn)較多[81]。

2.2 西葫蘆黃脈病毒Squashveinyellowingvirus(SqVYV)

SqVYV可以侵染葫蘆科的多種植物,侵染西瓜引起西瓜藤衰退,是嚴(yán)重危害西瓜生產(chǎn)的病害之一[85-87]。不同于potyviruses,Webster等發(fā)現(xiàn)佛羅里達(dá)地區(qū)的SqVYV種群具有較高的遺傳相似性,其分離物僅可形成兩個分組,且組間遺傳差異較小[88]。SqVYV佛羅里達(dá)種群受到負(fù)選擇壓力的作用明顯,尚未發(fā)現(xiàn)有正向選擇位點(diǎn),且其重組發(fā)生頻率較低,受到建立者效應(yīng)的影響顯著[88]。

2.3 木薯褐條病毒Cassavabrownstreakvirus(CBSV)

木薯褐條病是東非地區(qū)木薯上的主要病毒病害類型之一[89],是由CBSV和近年來新發(fā)生的另外一種病毒——烏干達(dá)木薯褐條病毒Ugandancassavabrownstreakvirus(UCBSV)引起的[90-91]。CBSV和UCBSV遺傳關(guān)系較近,核酸和氨基酸相似性分別在70%和74%左右。Mbanzibwa等發(fā)現(xiàn)兩種病毒分別存在較高頻率的重組現(xiàn)象,但未發(fā)現(xiàn)兩種病毒間存在重組。CBSV的CP基因和UCBSV的HAM1h基因中存在部分堿基處于正向選擇壓力作用下,表明CBSV和UCBSV可能處于不同的進(jìn)化過程中[92]。

3 禾草病毒屬Poacevirus

3.1 麥類花葉病毒Triticummosaicvirus(TriMV)

TriMV是近幾年在小麥上發(fā)現(xiàn)的一種病毒[93-94],由小麥卷葉螨AceriatosichellaKeifer傳播[95],目前已在美國大平原地區(qū)廣泛發(fā)生[93-94, 96-97]。Bartels等發(fā)現(xiàn)TriMV在同一寄主中進(jìn)化過程主要受到遺傳漂變的影響,不同代際間TriMV核苷酸突變具有很強(qiáng)的隨機(jī)性,CP基因突變頻率約1.95×10-4/nt,低于小麥線條花葉病毒W(wǎng)heatstreakmosaicvirus(WSMV),且具有平行進(jìn)化的特點(diǎn)[98]。

3.2 甘蔗線條花葉病毒Sugarcanestreakmosaicvirus(SCSMV)

SCSMV首先在甘蔗花葉病株上發(fā)現(xiàn),自然條件下能夠侵染甘蔗、高粱和一些禾本科雜草[99-105]。Viswanathan等[106]和Bagyalakshmi等[107]發(fā)現(xiàn)SCSMV印度分離物在CP和HC-Pro基因上存在較高的遺傳多樣性。SCSMV具有一個典型的“準(zhǔn)種”結(jié)構(gòu),普遍存在同種病毒不同分離物或株系混合侵染的現(xiàn)象;SCSMV在中印兩國間存在兩個獨(dú)立遺傳的種群,且種群間基因交換的頻率很低[108-110]。

4 問題與展望

綜上所述,目前已經(jīng)報道了多種potyvirids的分子進(jìn)化研究。單一potyvirids種群的分子進(jìn)化過程受到突變、重組、漂變、選擇壓力和遷移的共同作用。突變是促進(jìn)potyvirids種群分子進(jìn)化的主要作用力,potyvirids具有較高頻率的核苷酸替代率,平均水平在10-4級[111-114];在大部分potyvirids,特別是potyviruses基因組中,重組發(fā)生的頻率都很高,同種或者近緣病毒的分子間或者分子內(nèi)重組,是potyvirids增強(qiáng)種群適合度,增加寄主適應(yīng)性的主要方式之一,亦是當(dāng)前很多新型病毒產(chǎn)生或者老病毒某些新株系重新活躍的重要原因[115-118];漂變決定了Potyviridae進(jìn)化的隨機(jī)性和不可逆性,多種potyvirids種群在某些地區(qū)或者寄主中的進(jìn)化受到漂變,特別是建立者效應(yīng)的重要影響[16,18];選擇壓力對病毒進(jìn)化具有定向選擇的作用,potyvirids基因組受到負(fù)選擇壓力作用的影響顯著,證明了Potyviridae進(jìn)化上的保守性,而在P1、HC-Pro、P3和CP等基因中存在不同數(shù)量的正向選擇位點(diǎn),這顯示了獨(dú)特的地理環(huán)境和寄主條件對Potyviridae的定向選擇作用[30,44,75,108-109,119];potyvirids一般具有較為廣泛的寄主范圍,多種potyvirids在主要危害作物和其他寄主間的比較進(jìn)化研究表明,potyvirids在寄主間的遷移,對其進(jìn)化具有重要影響[75,98]。

研究病毒的分子進(jìn)化,很重要的目的是在分子水平上揭示病毒的進(jìn)化歷史,重演病毒在不同地區(qū)、不同寄主上的流行傳播過程[115-116,120]。然而,目前大部分potyvirids的進(jìn)化研究局限于單一種群,單一寄主中病毒進(jìn)化影響因素的闡釋。在今后的研究中,應(yīng)當(dāng)廣泛考慮病毒-寄主-介體-環(huán)境等多方面的因素,從分子生態(tài)學(xué)和種群生態(tài)學(xué)的角度,還原病毒起源、進(jìn)化和流行傳播過程,從而為病毒病害的防治提供合理的預(yù)防策略。

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(責(zé)任編輯：楊明麗)

Advances in molecular evolution of viruses in the familyPotyviridae

He Zhen1,2, Chen Chunfeng1, Zhang Zhixiang2, Li Shifang2

(1. School of Horticulture and Plant Protection, Yangzhou University, Yangzhou 225009, China;2. State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of PlantProtection, Chinese Academy of Agricultural Sciences, Beijing 100193, China)

Potyviridaeis one of important groups of plant viruses, and some species are significant pathogens in crop production. In the present review, we summarized the molecular evolution of more than 20 virus species in the generaPotyvirus,Ipomovirus, andPoacevirusof the familyPotyviridae, discussed some factors influencing mutation, recombination, genetic drift, selection and migration of potyvirids, and proposed future research directions, in order to provide effective strategies for prevention and control of the potyvirids.

Potyviridae; molecular evolution

2016-06-07

2016-07-15

國家自然科學(xué)基金(31601604);公益性行業(yè)(農(nóng)業(yè))科研專項(201303028);江蘇省高校自然科學(xué)基金(16KJB210015)

S 435.32

A

10.3969/j.issn.0529-1542.2017.03.003

* 通信作者 E-mail:sfli@ippcaas.cn