陳志騰,杜予州
(揚(yáng)州大學(xué)園藝與植物保護(hù)學(xué)院應(yīng)用昆蟲(chóng)研究所,江蘇揚(yáng)州 225009)
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昆蟲(chóng)線粒體基因組重排的研究進(jìn)展
陳志騰,杜予州*
(揚(yáng)州大學(xué)園藝與植物保護(hù)學(xué)院應(yīng)用昆蟲(chóng)研究所,江蘇揚(yáng)州 225009)
動(dòng)物線粒體基因組通常組成穩(wěn)定,基因排列也相對(duì)保守,極少發(fā)生重組。但是昆蟲(chóng)的線粒體基因組具有重排的可能性,而且這些重排事件可能為系統(tǒng)發(fā)育研究提供重要的信息。因此,深入研究昆蟲(chóng)線粒體基因組的重排可能有助于解決具有爭(zhēng)議的系統(tǒng)發(fā)生關(guān)系。本文對(duì)昆蟲(chóng)線粒體基因組的重排類(lèi)型、重排機(jī)理和重排在昆蟲(chóng)系統(tǒng)發(fā)育分析中的應(yīng)用等方面的研究進(jìn)展進(jìn)行了介紹。
線粒體基因組;昆蟲(chóng);基因重排;系統(tǒng)進(jìn)化;系統(tǒng)發(fā)育
昆蟲(chóng)的線粒體基因組(mitochondrial genome)通常為雙鏈閉合的環(huán)狀DNA分子,長(zhǎng)15-20 kb,一般包含37個(gè)基因,即13個(gè)蛋白質(zhì)編碼基因(PCG)、22個(gè)轉(zhuǎn)運(yùn)RNA(tRNA)基因和2個(gè)核糖體RNA(rRNA)基因,此外還有一個(gè)最大的非編碼區(qū),即控制區(qū)(Boore, 1999)。昆蟲(chóng)線粒體基因組的多數(shù)基因在同一條鏈上編碼,該鏈稱(chēng)為J鏈(majority strand),少數(shù)基因在另一條鏈上編碼,該鏈稱(chēng)為N鏈(minority strand)(Simonetal., 1994)。線粒體基因組具有分子量小、進(jìn)化速率快和重組水平較低等特點(diǎn),因此已經(jīng)被作為分子標(biāo)記在昆蟲(chóng)系統(tǒng)學(xué)等研究中得到廣泛應(yīng)用(Wilsonetal., 2000; Lin and Danforth, 2004; Gissietal., 2008; Salvatoetal., 2008; Wangetal., 2014a; Wangetal., 2015; Amaraletal., 2016; Songetal., 2016)。
自從第一個(gè)昆蟲(chóng)線粒體基因組,即果蠅Drosophilayakuba的線粒體基因組被測(cè)序(Claryetal., 1985)以來(lái),隨著分子生物學(xué)技術(shù)和昆蟲(chóng)線粒體基因組研究技術(shù)的不斷進(jìn)步,被測(cè)定的昆蟲(chóng)線粒體基因組的數(shù)量迅速增加,目前GenBank中已有超過(guò)790種昆蟲(chóng)的線粒體基因組被測(cè)序。隨著昆蟲(chóng)線粒體基因組全序列數(shù)據(jù)的逐漸增加,昆蟲(chóng)線粒體基因的重排現(xiàn)象也不斷被發(fā)現(xiàn)(Crozier and Crozier, 1993; Flooketal., 1995; Szymuraetal., 1996; Shao and Barker, 2003; Thaoetal., 2004; 魏書(shū)軍,2009;Tayetal., 2014; Wangetal., 2014b),本文就不同類(lèi)別昆蟲(chóng)的線粒體基因重排、常見(jiàn)的重排類(lèi)型、可能的重排機(jī)制以及重排在系統(tǒng)發(fā)生上的應(yīng)用等方面的研究進(jìn)展做了介紹。
昆蟲(chóng)中線粒體基因排列比較保守,一般把果蠅的線粒體基因排列方式作為昆蟲(chóng)的模式排列方式(圖1),大多數(shù)昆蟲(chóng)的線粒體基因都遵循這個(gè)排列順序,但有些類(lèi)群會(huì)在進(jìn)化過(guò)程中發(fā)生重排(Boore, 1999),因此昆蟲(chóng)線粒體基因的重排是相對(duì)于果蠅的線粒體基因來(lái)說(shuō)的。在昆蟲(chóng)中,目前已在17個(gè)目中發(fā)現(xiàn)有線粒體基因重排現(xiàn)象,即膜翅目、鱗翅目、雙翅目、脈翅目、毛翅目、捻翅目、鞘翅目、纓翅目、半翅目、虱目、嚙蟲(chóng)目、直翅目、彈尾目、石蛃目、原尾目、紡足目和革翅目。
圖1 推測(cè)的昆蟲(chóng)線粒體基因原始排列方式Fig.1 Putative ancestral mitochondrial gene arrangement of insects注:加下劃線的基因編碼于N鏈,未加下劃線的編碼于J鏈。Note: Underlined genes are encoded on minority strand while non-underlined genes are encoded on majority strand.
在六足總綱中,各個(gè)目之間發(fā)生的線粒體基因重排是隨機(jī)的,與各類(lèi)群的進(jìn)化關(guān)系沒(méi)有直接關(guān)聯(lián)(Cameronetal., 2006)?,F(xiàn)在已經(jīng)在昆蟲(chóng)的17個(gè)目中發(fā)現(xiàn)了線粒體基因重排,但他們?cè)谥嘏诺陌l(fā)生頻率和規(guī)模上也有區(qū)別。線粒體基因重排較多的目中,所有類(lèi)群都檢測(cè)到了基因的重排,重排涉及的基因數(shù)量很多,包括蛋白質(zhì)編碼基因、rRNA基因和tRNA基因,如虱目、嚙蟲(chóng)目、纓翅目和膜翅目等(Dowton and Austin, 1999; Dowtonetal., 2002a),其中虱目、嚙蟲(chóng)目和纓翅目的重排現(xiàn)象不僅在重排熱區(qū)發(fā)生,在一些非常保守的區(qū)域也有發(fā)生(Schmidt and Barker, 2001)。重排較少的目中,發(fā)生重排的種類(lèi)和涉及的基因數(shù)量一般較少,如半翅目、雙翅目和鞘翅目等。在有些目中,所有種類(lèi)都有相同的基因重排,并且基因重排可能是某些類(lèi)群的共有衍征,如鱗翅目(魏書(shū)軍和陳學(xué)新,2011;Caoetal., 2012)。
2.1膜翅目
膜翅目昆蟲(chóng)的線粒體基因重排具有多種類(lèi)型,包括基因洗牌、移位和倒置(Dowton and Austin, 1999)。此外,膜翅目昆蟲(chóng)的線粒體基因重排還有以下特點(diǎn):重排速率較高、重排程度在各類(lèi)群間有差異、重排以tRNA重排為主、不同類(lèi)型的重排所占比例幾乎相同等等(魏書(shū)軍,2009;Weietal., 2009; Weietal., 2010a; Weietal., 2010b)。Wei等(2014)首次報(bào)道了針尾亞目(Aculeata)中出現(xiàn)的線粒體蛋白編碼基因的重排,并且這些重排在膜翅目的大多類(lèi)群中是獨(dú)立進(jìn)化的。每種已測(cè)序的膜翅目昆蟲(chóng)都有至少一個(gè)易位的tRNA,并且在COII-ATP8、ND3-ND5、ND2-COI、控制區(qū)-ND2基因連接部是膜翅目昆蟲(chóng)線粒體基因組中tRNA重排的多發(fā)區(qū)(Dowton, 1999; Dowton and Austin, 1999; Dowtonetal., 2003)。線粒體基因組的比較研究表明,廣腰亞目的基因排列比細(xì)腰亞目保守,即細(xì)腰亞目比廣腰亞目的基因重排頻率高;但相對(duì)于其他目的大多數(shù)昆蟲(chóng)來(lái)說(shuō),廣腰亞目的基因重排更加頻繁(Dowton and Austin, 1999; Dowtonetal., 2003; Songetal., 2016)。有研究發(fā)現(xiàn),膜翅目中獨(dú)特的重排非常常見(jiàn),在已鑒定的67個(gè)重排中,只有5個(gè)是在兩個(gè)或多個(gè)物種中共享的,并且5個(gè)重排中只有2個(gè)是真正同源的(Dowtonetal., 2009)。Maoetal. (2014) 在胡峰Conostigmussp. 中檢測(cè)到了線粒體基因組小環(huán),這為基因重組和線粒體基因重排之間的聯(lián)系提供了支持。魏書(shū)軍(2009)還發(fā)現(xiàn),在膜翅目昆蟲(chóng)的線粒體基因組中,有重疊部分的基因很少發(fā)生重排,而發(fā)生重排的基因兩側(cè)通常有基因間隔部分。
2.2鱗翅目
大多數(shù)鱗翅目昆蟲(chóng)線粒體基因的排列順序不同于果蠅,而是與第一個(gè)被測(cè)序的鱗翅目昆蟲(chóng)家蠶一致(王維等,2013)。鱗翅目中,已測(cè)定的線粒體基因組除了具有原始排列的種類(lèi)之外,還包括典型的trnM-trnI-trnQ重排順序,以及trnA-trnF基因簇中的基因重排(Caoetal., 2012; Gongetal., 2012; Wangetal., 2014a; Parketal., 2016)。但是,鱗翅目的原始類(lèi)群仍然需要更多測(cè)序工作來(lái)深入研究。
2.3雙翅目
雙翅目中,線粒體基因發(fā)生重排的種類(lèi)集中在長(zhǎng)角亞目Nematocera中(魏書(shū)軍,2009)。在雙翅目中比較普遍的重排現(xiàn)象是tRNA基因的增加或者發(fā)生基因倒置,轉(zhuǎn)移到另一條鏈上(de Azeredo-Espin, 2004; Yuetal., 2007)。進(jìn)化程度較高的種類(lèi)基因重排并不頻繁,較常見(jiàn)的只是涉及個(gè)別tRNA基因的重排;而在低等的雙翅目中,線粒體基因的重排很明顯,涉及到tRNA基因的位置以及蛋白質(zhì)編碼基因的位置(Beckenbach, 2012;梅琰等,2012)。
2.4鞘翅目
鞘翅目中,線粒體基因組的基因排列順序和組成相對(duì)保守。目前已知的鞘翅目線粒體基因組的基因組成,特別是蛋白質(zhì)編碼基因的排列大多與祖先昆蟲(chóng)一致,基因重排較少(Timmermans and Vogler, 2012)。例如,在花蚤Mordellaatrata和象甲Naupactusxanthographus中發(fā)生的tRNA重排(Songetal., 2010)。除了tRNA發(fā)生重排之外,在花螢科的Phrixtothrixhirtus和叩甲科的Teslasenafemoralis中還觀察到了控制區(qū)的位置變化(Amaraletal., 2016)。
2.5纓翅目
纓翅目(薊馬)中已測(cè)線粒體基因組的種類(lèi)有澳洲疫薊馬Thripsimaginis、西花薊馬Frankliniellaoccidentalis、茶黃薊馬Scirtothripsdorsalis、花薊馬Frankliniellaintonsa和稻管薊馬Haplothripsaculeatus(Shao and Barker, 2003; Yanetal., 2012; Yanetal., 2014; Dickeyetal., 2015),并且它們的線粒體基因組都高度重排。在澳洲疫薊馬T.imaginis中出現(xiàn)了2個(gè)非常相似的A+T富含區(qū)(Shao and Barker, 2003),在西花薊馬F.occidentalis和花薊馬F.intonsa中也都出現(xiàn)了3個(gè)控制區(qū)(Yanetal., 2014)。此外,在茶黃薊馬S.dorsalis的南亞1種群中,還出現(xiàn)了裂化的線粒體基因組,即同時(shí)具有兩個(gè)環(huán)狀的染色體(Dickeyetal., 2015)。系統(tǒng)發(fā)育研究表明,這幾個(gè)已測(cè)序的種類(lèi)所在的屬(薊馬屬、花薊馬屬)是薊馬科中種類(lèi)最為豐富的屬,也是最為進(jìn)化的支系,這暗示著薊馬的線粒體基因在早期大量重排后,經(jīng)過(guò)長(zhǎng)期的進(jìn)化現(xiàn)已保持穩(wěn)定(Buckmanetal., 2013; Yanetal., 2014)。
2.6半翅目(廣義)
已測(cè)序線粒體基因組的半翅目昆蟲(chóng)中,大多數(shù)種類(lèi)的線粒體基因排列與模式昆蟲(chóng)果蠅相同。半翅目中的3個(gè)亞目的昆蟲(chóng)都包含高度重排的類(lèi)群,即半翅目中胸喙亞目Sternorrhyncha的粉虱科Aleyrodidae、異翅亞目Heteroptera的光背奇蝽屬Stenopirates的個(gè)別種類(lèi)以及一些涉及tRNA重排的個(gè)例(Thaoetal., 2004; Lietal., 2012; Lietal., 2016)。在粉虱科中,已經(jīng)測(cè)序的12個(gè)種中就有8個(gè)種發(fā)生了線粒體基因重排,并且這些重排都涉及ND3-trnG-COIII基因簇的變動(dòng)。
2.7嚙蟲(chóng)目及虱目
近年來(lái)的研究表明,嚙蟲(chóng)目和虱目的親緣關(guān)系很近,并將二者組成一個(gè)總目,即嚙總目(Yoshizawaetal., 2006)。相比于其它目的昆蟲(chóng),嚙總目昆蟲(chóng)的線粒體基因組具有豐富的變異性,而且會(huì)發(fā)生裂化,即裂化成數(shù)個(gè)線粒體基因組小環(huán)(魏丹丹等,2014)。線粒體基因組的裂化為線粒體基因的重組提供了直接證據(jù),說(shuō)明線粒體基因組之間有同源與非同源性的重組(Shao and Barker, 2011)。線粒體基因組在裂化后會(huì)出現(xiàn)假基因,這可能是不同線粒體基因組環(huán)之間經(jīng)歷重組和刪除后的痕跡(Weietal., 2012)。
對(duì)于嚙蟲(chóng)目而言,已測(cè)定的各種類(lèi)線粒體基因組之間的基因排列均有差異(Shaoetal., 2001b)。在Liposcelisbostrychophila中,典型的單個(gè)線粒體基因組分裂成為兩個(gè),這種分裂的情況可能為物種帶來(lái)一些進(jìn)化的優(yōu)勢(shì)(Weietal., 2012)。但是相同屬中的L.decolor的線粒體基因排列卻與L.bostrychophila有很大差異,這種情況在動(dòng)物中很罕見(jiàn)(Chenetal., 2014)。
虱目昆蟲(chóng)的線粒體基因組在所有節(jié)肢動(dòng)物中是重排最多的(Shaoetal., 2001a),并且保留祖先昆蟲(chóng)的原始基因邊界極少,最多的也僅僅保留3個(gè),即發(fā)生在Bothriometopusmacrocnemis的線粒體基因組中(Cameronetal., 2007)。在B.macrocnemis中,基因重排導(dǎo)致了所有的基因均由J鏈編碼,即轉(zhuǎn)錄方向一致,這在昆蟲(chóng)中是個(gè)特例(Cameronetal., 2007)。在Heterodoxusmacropus中所有tNRA基因和9種蛋白質(zhì)基因均發(fā)生重排,并存在2個(gè)A+T富含區(qū)(Shaoetal., 2001a)。此外,除了來(lái)自Gonioidae科的兩個(gè)非常緊密相關(guān)的物種之外,虱目之間共享的異?;蛑嘏欧浅I?Cameron, 2014)。
2.8直翅目
直翅目的蝗亞目Caelifera昆蟲(chóng)中普遍存在trnK與trnD順序顛倒(DK 重排)的現(xiàn)象,但有個(gè)例外就是日本蚤螻Tridactylusjaponicus,這個(gè)種類(lèi)沒(méi)有發(fā)生線粒體基因重排(Sheffieldetal., 2010; Zhaoetal., 2010; 王鵬翔,2013)。在螽斯亞目Ensifera的黃臉油葫蘆Teleogryllusemma中,具有ARESNF結(jié)構(gòu)的tRNA排列方式(葉偉等,2008)。此外,在樹(shù)螽Phyllomimusdetersus中,還包括trnM-trnI-trnQ的獨(dú)特重排順序(Yangetal., 2016)。
2.9其它目
毛翅目:毛翅目中已經(jīng)測(cè)定的5個(gè)種中,只有Hydropsychepellucidula的srRNA和兩個(gè)tRNA(trnP和trnI)發(fā)生了重排(Linardetal., 2015)。
脈翅目:脈翅目中測(cè)定的15個(gè)種中只有部分涉及到trnC的轉(zhuǎn)置。
彈尾目:在彈尾目已測(cè)定線粒體基因組的10個(gè)種中,只有3個(gè)種涉及到tRNA的重排,其余均與模式昆蟲(chóng)果蠅的基因排列方式一致。
紡足目:目前僅已知一種紡足目昆蟲(chóng)Aposthoniajaponica的線粒體基因組,而且其具有trnD-ND5基因簇的重排以及1個(gè)額外復(fù)制的srRNA基因(Kmotoetal., 2012)。
革翅目:目前僅有一種革翅目昆蟲(chóng)Challiafletcheri的線粒體基因組已經(jīng)測(cè)序,其中涉及到7個(gè)tRNA的重排(Wanetal., 2012)。
迄今為止,根據(jù)不同的劃分標(biāo)準(zhǔn),線粒體基因的重排可以分為幾種不同的類(lèi)型。根據(jù)線粒體基因組重排基因的種類(lèi)可以分為主要重排(major rearrangement),即包含蛋白質(zhì)編碼基因或rRNA基因的重排,以及次要重排(minor rearrangement),即只包含tRNA基因的重排(Cameronetal., 2007)。
根據(jù)基因重排中基因的位置變化可以分為(1)基因洗牌(shuffling),即基因在同一條鏈上從一個(gè)位置滑移到相鄰位置,距離一般很短,而且一般不會(huì)跨越蛋白基因;(2)基因移位(translocation),即基因從原始位置跨越蛋白質(zhì)或rRNA基因重排到不同的位置;(3)基因倒置(inversion),即基因從一條編碼鏈轉(zhuǎn)換到另外一條編碼鏈編碼,這種基因編碼鏈的轉(zhuǎn)換,會(huì)導(dǎo)致其閱讀方向的改變,并且發(fā)生倒置的基因在基因組上的排列位置變化并不大?;虻怪糜职ㄔ坏怪?local inversion),即基因的相對(duì)位置不變,方向改變(Dowton and Austin, 1999),以及異位倒置(remote inversion),即基因的相對(duì)位置和方向都發(fā)生改變(Dowtonetal., 2003)。倒置在昆蟲(chóng)中是最不常見(jiàn)的重排類(lèi)型,在革翅目(Wanetal., 2012)、膜翅目(Dowtonetal., 2009)和3個(gè)準(zhǔn)新翅類(lèi)(Paraneoptera)(Shaoetal., 2001b; Shao and Barker, 2003; Thaoetal., 2004; Weietal., 2012)中都有記錄。這些不同類(lèi)型的重排可能組合發(fā)生,而且一般認(rèn)為短距離的重排比長(zhǎng)距離的重排更加頻繁(Dowtonetal., 2009)。
目前用于解釋線粒體基因重排的機(jī)制主要有:(1)復(fù)制-隨機(jī)丟失(duplication-random loss)(Moritz and Brown, 1987);(2)復(fù)制-非隨機(jī)丟失(duplication-nonrandom loss)(Lavrovetal., 2002);(3)重組(Recombination)(Poultonetal., 1993; Lunt and Hyman, 1997; Dowton and Campbell, 2001);(4)由tRNA 基因錯(cuò)誤起始引起的復(fù)制(illicit priming of replication by tRNA genes)(Cantatoreetal., 1987)。
4.1復(fù)制-隨機(jī)丟失
復(fù)制-隨機(jī)丟失是用于解釋線粒體基因重排的最廣泛被接受的機(jī)制,該模型由Moritz and Brown(1987)最早提出,并由Maceyetal.(1997)和Boore and Brown(1998)進(jìn)行了完善。在復(fù)制-隨機(jī)丟失模型中,一部分線粒體基因由于復(fù)制產(chǎn)生了多基因的重復(fù),其中復(fù)制可能是通過(guò)滑鏈錯(cuò)配(slipped-strand mispairing)、非精確終止(imprecise termination)、基因組的二聚作用(dimerization of the genome)或重組(recombination)(Moritz and Brown, 1987)。隨后,在多基因重復(fù)內(nèi)突變的積累最終使其中一個(gè)基因失去功能,這時(shí)候縮小基因組的選擇性壓力就會(huì)導(dǎo)致無(wú)功能基因的消除(Rand, 1994)。復(fù)制-隨機(jī)丟失模型很容易解釋基因移位但不能解釋基因倒置。在昆蟲(chóng)中,復(fù)制-隨機(jī)丟失模型解釋了大多數(shù)觀察到的線粒體基因重排,而在脊椎動(dòng)物中它解釋了幾乎所有觀察到的重排現(xiàn)象(Dowtonetal., 2009)。
4.2復(fù)制-非隨機(jī)丟失
復(fù)制-非隨機(jī)丟失模型由Lavrovetal.(2002)提出。該模型中,線粒體基因組先整體復(fù)制,形成一個(gè)首尾相連的環(huán)狀二聚體分子,然后根據(jù)基因的轉(zhuǎn)錄方向和位置進(jìn)行非隨機(jī)的刪除(Lavrovetal., 2002)。該模型與與復(fù)制-隨機(jī)丟失模型相似,只是基因的丟失受到基因組內(nèi)的轉(zhuǎn)錄模塊的限制;在這些轉(zhuǎn)錄模塊邊界的重復(fù)基因不能被表達(dá)所以被消除,因此基因缺失是非隨機(jī)性的(Lavrovetal., 2002)。復(fù)制-非隨機(jī)丟失模型不常被用于解釋昆蟲(chóng)中的重排,但它能解釋雙翅目等物種中極性相同的基因聚集的特殊現(xiàn)象(Beckenbach, 2012)。
4.3重組
重組模型由Poultonetal.(1993)首次提出。在該模型中,一個(gè)完整的線粒體基因組在多個(gè)位點(diǎn)斷裂,斷裂后的片段在重組時(shí)由于順序變化導(dǎo)致基因重排。雖然線粒體重組在歷史上有爭(zhēng)論(Moritz and Brown, 1987),但解釋基因倒置和大片段基因的相鄰互換就不能缺少某種形式的重組(Dowton and Campbell, 2001)。此外,該模型是解釋膜翅目昆蟲(chóng)線粒體基因重排的重要機(jī)制之一(Dowton and Austin, 1999)。
4.4由tRNA 基因錯(cuò)誤起始引起的復(fù)制
由tRNA 基因錯(cuò)誤起始引發(fā)的線粒體基因組復(fù)制模型由Cantatoreetal.(1987)首次提出。當(dāng)tRNA 作為復(fù)制起點(diǎn)引起線粒體基因組復(fù)制時(shí),該tRNA仍存在于新的DNA鏈上,隨后這個(gè)tRNA可能被作為模板而被復(fù)制,從而可能導(dǎo)致該tRNA被組合到線粒體基因組的復(fù)制起點(diǎn),使線粒體復(fù)制錯(cuò)誤產(chǎn)生基因重排現(xiàn)象。
目前人們?cè)诜治隼ハx(chóng)線粒體基因重排頻率加速的原因時(shí),大多集中于把生活史特性作為重排事件的預(yù)測(cè)因子。由于在幾個(gè)寄生性昆蟲(chóng)種群中發(fā)現(xiàn)了高度重排的線粒體基因組,所以寄生習(xí)性多次被認(rèn)為是誘發(fā)因素(Shaoetal., 2001a; Dowtonetal., 2002b)。但隨著線粒體基因組測(cè)序的種類(lèi)增多,有研究發(fā)現(xiàn),在雙翅目昆蟲(chóng)中寄生狀態(tài)和重排之間沒(méi)有相關(guān)性,但在膜翅目中具有相關(guān)性(Castroetal., 2002)。然而隨后的深入研究表明,膜翅目中加速的重排頻率并不與這個(gè)目?jī)?nèi)寄生習(xí)性的進(jìn)化情況相一致,從而基本否定了寄生這個(gè)因素對(duì)重排加速的作用(Dowtonetal., 2009)。這些研究還表明,在寄生的類(lèi)群中,加速的重排和核苷酸替代比率之間有明顯的相關(guān)性(Castroetal., 2002; Shaoetal., 2003)。
重排加速的第二個(gè)原因是控制區(qū)的復(fù)制,這已經(jīng)在薊馬和嚙蟲(chóng)目中得到證實(shí)(Shao and Barker, 2003; Shaoetal., 2005; Yanetal., 2012)。雖然控制區(qū)的復(fù)制對(duì)重排速率的影響尚未充分了解,但是薊馬的控制區(qū)實(shí)際上是符合穩(wěn)定的基因組排列的,原因是這兩個(gè)含有重復(fù)控制區(qū)的薊馬種群之間只存在6個(gè)tRNA的重排(Cameron, 2014)。
重排加速的第三個(gè)原因可能與單倍二倍體(haplodiploidy)的進(jìn)化有關(guān)。在8個(gè)具有獨(dú)立進(jìn)化的單倍二倍性的昆蟲(chóng)群體中,除了有4個(gè)種的線粒體基因組數(shù)據(jù)尚未獲得外,另外4個(gè)群體(膜翅目、纓翅目、粉虱科、眼蕈蚊科)具有加速的重排(Normark, 2003)。但有個(gè)例外是虱子,即虱子本身并沒(méi)有單倍二倍性,但它會(huì)進(jìn)行父性基因組的消除,從而產(chǎn)生與經(jīng)典的單倍二倍體相似的基因組遺傳模式(McMeniman and Barker, 2006; Cameron, 2014)。
總之,昆蟲(chóng)中線粒體基因發(fā)生重排的原因可能是多方面的,并且需要進(jìn)行更深入的研究。
一般來(lái)說(shuō),線粒體基因重排是一類(lèi)被稱(chēng)為“罕見(jiàn)的基因組改變(rare genomic changes,RGCs)”的系統(tǒng)發(fā)育標(biāo)記,并且它們的相似性很低(Rokas and Holland, 2000)。理論上,使用線粒體基因重排作為系統(tǒng)發(fā)育標(biāo)記是有利的,原因如下:(1)線粒體基因組的重排基因數(shù)據(jù)集在兩側(cè)對(duì)稱(chēng)動(dòng)物中幾乎不變;(2)重排基因的同源性通常是清楚的;(3)重排事件似乎不太常見(jiàn);(4)基因順序明顯選擇性地保持中性;(5)由于潛在基因順序的數(shù)量巨大,趨同的可能性通常很低(Boore and Brown, 1998)。
昆蟲(chóng)中的基因重排事件對(duì)昆蟲(chóng)各目之間的系統(tǒng)發(fā)育關(guān)系的研究貢獻(xiàn)不大,但是可能有利于研究昆蟲(chóng)目?jī)?nèi)各類(lèi)群之間的系統(tǒng)發(fā)育關(guān)系(Cameronetal., 2006; Cameron, 2014)。目前將基因重排現(xiàn)象應(yīng)用于昆蟲(chóng)的系統(tǒng)發(fā)育研究方面的研究很少,主要因?yàn)橐呀?jīng)研究過(guò)的重排現(xiàn)象和類(lèi)群非常少。因?yàn)榛蛑嘏艣](méi)有分子鐘,即沒(méi)有分子進(jìn)化速度的恒定性,所以具有相同基因排列的物種可能來(lái)自共同的祖先,但也可能是由于在短期內(nèi)快速發(fā)生過(guò)多的重排事件導(dǎo)致的,這對(duì)線粒體基因重排在系統(tǒng)發(fā)育中的應(yīng)用會(huì)產(chǎn)生干擾,因此要嚴(yán)格辨別(Yi, 2007)。
目前已經(jīng)測(cè)定的昆蟲(chóng)線粒體基因組幾乎覆蓋了所有的目,但有些目的線粒體基因組已測(cè)序的種類(lèi)很少,應(yīng)用這些序列進(jìn)行大規(guī)模的目與目之間的線粒體基因組比較研究來(lái)說(shuō),還是很有限的,因此對(duì)更多的昆蟲(chóng)類(lèi)群,特別是對(duì)一些重要類(lèi)群的線粒體基因組進(jìn)行測(cè)序和分析,顯得尤為重要。由于昆蟲(chóng)中的線粒體基因重排事件蘊(yùn)含著與物種系統(tǒng)進(jìn)化相關(guān)的遺傳信息,因此需要對(duì)昆蟲(chóng)各目的線粒體基因重排進(jìn)行更透徹和系統(tǒng)的研究。此外,在利用線粒體基因的重排信息來(lái)重建系統(tǒng)發(fā)育關(guān)系時(shí),仍然存在許多制約因素,因此要深入研究并且利用基因重排所透露的遺傳信息去更好地解決具有爭(zhēng)議的系統(tǒng)進(jìn)化問(wèn)題。
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Rearrangement of mitochondrial genome in insects
CHEN Zhi-Teng, DU Yu-Zhou*
(School of Horticulture and Plant Protection & Institute of Applied Entomology, Yangzhou University, Yangzhou 225009, Jiangsu Province,China)
Generally, animal mitochondrial genomes have stable gene content, relatively conserved gene arrangement and infrequent recombination. However, insect mitochondrial genomes have the potential of rearrangement, which might provide important information for phylogenetic studies, and further study into this tool may contribute to resolving the debatable phylogeny. This paper reviewed progress in this field, including types, mechanisms of gene rearrangement in insects and its utilization in phylogenetic analysis.
Mitochondrial genome; insects; gene rearrangement; phylogenetic evolution; phylogeny
國(guó)家自然科學(xué)基金項(xiàng)目(31572295)
陳志騰,男,1990年生,江蘇南通人,博士研究生,研究方向?yàn)槔ハx(chóng)系統(tǒng)學(xué),E-mail: 741208116@qq.com
Author for correspondence,E-mail: yzdu@yzu.edu.cn
2016-04-17; 接受日期 Accepted: 2016-05-09
Q963
A
1674-0858(2016)04-0843-09