柴松岳,姚 琴,程怡然,王 超,周永紅,王 益
(四川農(nóng)業(yè)大學(xué)小麥研究所,成都 611130)
利用SLAF-Seq-BSA定位矮稈波蘭小麥矮化基因Rht-dp
柴松岳,姚 琴,程怡然,王 超,周永紅,王 益*
(四川農(nóng)業(yè)大學(xué)小麥研究所,成都 611130)
【目的】為了顯著地縮小矮稈波蘭小麥矮化基因Rht-dp的候選區(qū)域?!痉椒ā拷柚鶶LAF-Seq-BSA(specific-locus amplified fragment sequencing and bulked segregant analysis)技術(shù)進(jìn)行Rht-dp的關(guān)聯(lián)分析。【結(jié)果】通過對親本、極高和極矮池的SLAF-Seq分析,SLAF標(biāo)簽均勻分布在A和B基因組上,但仍有部分標(biāo)簽分布在D基因組或沒有綁定在中國春基因組上。同時(shí)將Rht-dp定位在4B基因組上的154766 751-343858 300區(qū)域;結(jié)合前期SSR標(biāo)記分析結(jié)果(99826 939-250584 662),最終將Rht-dp縮小在4B基因組上的154766 751-250584 662區(qū)域?!窘Y(jié)論】矮稈波蘭小麥與中國春具有一定的遺傳差異。SLAF-Seq-BSA能有效地用于矮稈波蘭小麥矮化基因Rht-dp的定位,為后期建立其他分子標(biāo)記快速縮小目的區(qū)域奠定了物質(zhì)基礎(chǔ)。
矮稈波蘭小麥;SLAF-Seq;BSA;Rht-dp
株高影響植物倒伏、收獲指數(shù)以及產(chǎn)量。從發(fā)現(xiàn)和利用植物矮化基因開啟“綠色革命”至今,大量水稻、玉米以及小麥等矮化優(yōu)良品種應(yīng)用于農(nóng)業(yè)生產(chǎn)。因此,對農(nóng)作物等的矮化基因及其機(jī)制的研究也成為植物研究的熱點(diǎn)和重點(diǎn)。
目前,小麥中已經(jīng)發(fā)現(xiàn)和命名了24個(gè)矮化基因,共29個(gè)等位基因。這些等位基因中,20個(gè)來源于六倍體普通小麥(Triticum aestivu m,2n=6x=42),其中圍繞Rht-B1、Rht-D1、Rht-8和Rht 12的研究較多,它們通過干擾小麥體內(nèi)赤霉素的合成或轉(zhuǎn)導(dǎo)抑制莖稈的伸長導(dǎo)致矮化[1-4]。其余小麥矮化基因主要集中在簡單的基因定位和對赤霉素的敏感性檢測:其中16個(gè)為赤霉素敏感類型,13個(gè)為赤霉素不敏感類型[5];以及23個(gè)等位基因分別定位在小麥的2A、2B、3B、4B、4D、5A、5D、6A、7A 和 7B 染色體上[6-18]。同時(shí),這29個(gè)等位基因中,16個(gè)為隱性或部分隱性基因,13個(gè)為顯性或半顯性基因;以及14個(gè)為天然矮化基因,15個(gè)為人工誘變矮化基因(見表1)。
表1 小麥矮稈基因(24個(gè)基因,共29個(gè)等位基因)Table1 All dwarfing genes in wheat(24 genes,totally 29 alleles)
作為普通小麥的親緣物種,至今在四倍體小麥中先后發(fā)現(xiàn)9個(gè)矮化基因,分別是來源于硬粒小麥(T.turgidum)的 Rht14、Rht15、Rht16、Rht18 和 Rht19[8,11],圓錐小麥(T.durum)的 Rht22[12]和 Rht-B1f[13],以及波蘭小麥(T.polonicum)的Rht-B1IC12196[5]和Rht-dp[10]。與來源于日本波蘭小麥的顯性基因Rht-B1IC12196不同,Rht-dp為隱性主效基因且來源于我國新疆矮稈波蘭小麥(dwarf polish wheat,DPW,2n=4x=28,AABB,AS304)。2012 年 Kang H.Y.等[10]利用 SSR 標(biāo)記對DPW×高稈波蘭小麥的124個(gè)F2單株進(jìn)行了遺傳分析,發(fā)現(xiàn)該基因位于DPW的4BS染色體上,與SSR標(biāo)記Xwmc511和Xgpw3017連鎖且遺傳距離分別為5.5 cM和0.5 cM。與國際小麥基因組測序組織最新公布的中國春序列比對,發(fā)現(xiàn)Xwmc511和Xgpw3017之間具有約1.5億(99826 939~250584 662)個(gè)堿基序列。如此大的遺傳區(qū)間不能實(shí)現(xiàn)Rhtdp的基因克隆。因此,進(jìn)一步顯著性地縮小與Rhtdp連鎖的遺傳區(qū)域是實(shí)現(xiàn)Rht-dp基因克隆的前提保障。
得益于新一代測序技術(shù)的發(fā)展和應(yīng)用,高通量的分子標(biāo)記技術(shù)如單核苷酸多態(tài)性標(biāo)記(single nucleotide polymorphisms,SNP)芯片、多樣性芯片技術(shù)(diversity arrays technology,DArT)、SLAF-Seq-BSA(specific-locus amplified fragment sequencing and bulked segregant analysis)等已經(jīng)廣泛應(yīng)用于植物目標(biāo)性狀的定位或全基因組關(guān)聯(lián)分析。SLAF-Seq是一種高通量SNP挖掘和基因型鑒定技術(shù)[19]。群體分組分析法(BSA)通過構(gòu)建某一性狀的兩個(gè)極端群體能有效地檢測該性狀的位點(diǎn)[20]。這兩者的結(jié)合已經(jīng)廣泛應(yīng)用于小麥及其近緣物種目標(biāo)性狀的精細(xì)定位及其候選基因的選擇,如控制小麥粒重的TaTGW-7A[21]。因此,本研究借助SLAF-Seq-BSA技術(shù),對DPW×高稈波蘭小麥重組自交系(F7-8)群體構(gòu)建的兩個(gè)極高和極矮的庫進(jìn)行分析,以期顯著性地縮小Rht-dp的遺傳連鎖區(qū)域。
DPW、高稈波蘭小麥、DPW×高稈波蘭小麥重組自交系(F7-8)群體。DPW和高稈波蘭小麥均是采自于我國新疆吐魯番地區(qū)的自然分布的四倍體材料(2n=4x=28,AABB)。所有實(shí)驗(yàn)材料均種植在四川農(nóng)業(yè)大學(xué)崇州現(xiàn)代農(nóng)業(yè)研發(fā)基地,且保存在四川農(nóng)業(yè)大學(xué)小麥研究所。
對田間種植的DPW、高稈波蘭小麥、DPW×高稈波蘭小麥重組自交系(F7-8)進(jìn)行成熟期株高測量。親本及每個(gè)株系測量10個(gè)單株。同時(shí)在重組自交系中選擇30個(gè)最高株系以及30個(gè)最矮株系,并收集葉片保存在-20℃冰箱,為DNA提取備用。
親本及兩個(gè)重組自交系庫的SLAF測序及分析參照 Hu M.等[21]和 J.T.Hill等[22]的方法,并由北京百邁克生物技術(shù)有限公司完成。利用國際小麥基因組測序組織公布的中國春基因組(v1.0-assembly)為參考基因組。
在成熟期,高稈和矮稈波蘭小麥平均株高分別為165 cm和95 cm;極高和極低重組自交系混合池的平均株高分別為150 cm和87 cm(見圖1)?;旌铣亻g以及親本間株高差異顯著,符合SLAF-Seq-BSA分析要求。
圖1 成株期不同材料間的株高Figure1 Plant height of different materials at the maturation stage plant height
經(jīng)過酶切成460~480 bp片段后,測序共獲得18453 632~34557 031個(gè)讀序,質(zhì)量大于或等于30的堿基占 88.04%~88.83%,GC含量為 44.89%~45.61%。共獲得532907個(gè)SLAF標(biāo)簽,每個(gè)SLAF標(biāo)簽的親本測序深度為28.95×~29.01×,高稈和矮稈池測序深度分別為52.38×和43.70×。與中國春基因組比對,這些SLAF標(biāo)簽較均勻分布在各條A和B基因組上,其中3B基因組最多為46796個(gè),而1A基因組最少為29179個(gè)。但共有19648個(gè)SLAF標(biāo)簽位于D基因組或沒有綁定到中國春基因組上(見表2)。親本間和混池間分別獲得134779和145317個(gè)SNP。通過親本和混池過濾,共獲得37447個(gè)高質(zhì)量的SNP位點(diǎn)。
根據(jù)J.T.Hill等[22]的ED值計(jì)算方法,計(jì)算獲得所有位點(diǎn)擬合值的中間值作為關(guān)聯(lián)閾值為1.49。根據(jù)該閾值,獲得1個(gè)位于4B染色體上的關(guān)聯(lián)區(qū)域,總長度為5.20億個(gè)堿基(64715 030~585564 036,見圖 2),
表2 SLAF標(biāo)簽在基因組上的分布統(tǒng)計(jì)Table2 The distribution of SLAF tags on genomes
通過計(jì)算混池間基因型頻率的顯著差異,用Δ(SNP-index)統(tǒng)計(jì)。SNP標(biāo)記與性狀關(guān)聯(lián)度越強(qiáng),Δ(SNP-index)越接近1。通過計(jì)算,取擬合后的Δ(SNP-index)值0.91為關(guān)聯(lián)閾值(見圖3),在4B染色體上獲得一個(gè)總長度為1.89億個(gè)堿基的關(guān)聯(lián)區(qū)域。該區(qū)域在4B基因組上的起始位置為154766 751到343858 300。
綜合ED和SNP-index分析,SLAF-Seq-BSA將Rht-dp定位在4B基因組上的154766 751~343858 300區(qū)域。然而,Kang H.Y.等[10]的SSR標(biāo)記分析結(jié)果,即Rht-dp位于4B基因組上的99826 939~250584 662區(qū)域。因此,取這兩次分析的交集,最終將Rht-dp縮小在4BS基因組上的154766 751~250584 662區(qū)域,該區(qū)域具有約0.95億個(gè)堿基。該區(qū)域內(nèi)約有269個(gè)編碼基因(見表1),其中含有一個(gè)依賴 S-腺苷-L-蛋氨酸(S-adenosyl-L-methionine)的甲基轉(zhuǎn)移酶(Methyltransferase)。
圖2 歐式距離方法關(guān)聯(lián)分析Figure2 The euclidean distance correlated analysis
波蘭小麥與圓錐小麥、硬粒小麥和普通小麥的遺傳相似度較低[23-24]。同時(shí)能積累高濃度的鋅、鐵和銅等營養(yǎng)元素在種子中,以及具有高千粒重等因素,波蘭小麥也廣泛地受到育種家的重視[25]。同時(shí),相關(guān)研究也表明來源于中國的波蘭小麥與圓錐小麥、硬粒小麥和普通小麥的遺傳相似度更低[23]。矮稈波蘭小麥來源于我國新疆,對鋅和鎘等重金屬元素具有較高的耐受性[26]。盡管其攜帶的天然主效隱性矮化基因Rht-dp也位于4BS上,但利用Rht-B1進(jìn)行同源克隆,在高稈和矮稈波蘭小麥中我們沒有獲得與Rht-B1相似的基因序列。同時(shí),Rht-B1IC12196是一個(gè)顯性主效基因[5],其所在的4BS基因組區(qū)域與Rht-dp的區(qū)域不同。因此,Rht-dp與Rht-B1IC12196不同,是一個(gè)獨(dú)立起源于中國的矮化基因。同時(shí),本研究的SLAF-Seq分析發(fā)現(xiàn)共19648個(gè)SLAF標(biāo)簽位于D基因組或沒有綁定到中國春基因組上,表明這兩份波蘭小麥與中國春確實(shí)具有一定的遺傳差異,盡管未綁定的部分SLAF標(biāo)簽也可能是由于中國春參考基因組的不完善導(dǎo)致。
圖3 SNP-index關(guān)聯(lián)分析Figure3 The SNP-index correlated analysis
不同的矮化基因涉及不同的矮化機(jī)制。多數(shù)矮化基因干擾植物激素的合成、信號轉(zhuǎn)導(dǎo)或運(yùn)輸,抑制細(xì)胞的生長和分化而導(dǎo)致矮化。主要包含赤霉素、細(xì)胞分蘗素、油菜內(nèi)酯素、吲哚乙酸、獨(dú)腳金內(nèi)酯素等[27-30]。然而,還有部分矮化基因通過干擾苯丙氨酸途徑從而影響木質(zhì)素或異黃酮等物質(zhì)的合成導(dǎo)致矮化[31-32]。我們前期利用轉(zhuǎn)錄組和蛋白質(zhì)組學(xué)對矮稈波蘭小麥和高稈波蘭小麥在不同光照條件下的莖稈進(jìn)行分析,發(fā)現(xiàn)矮稈波蘭小麥的Rht-dp可能干預(yù)木質(zhì)素和纖維素合成,導(dǎo)致矮稈波蘭小麥莖稈的木質(zhì)素和纖維素含量降低從而導(dǎo)致矮化[26]。本研究利用SLAF-Seq-BSA分析和前期的SSR標(biāo)記分析結(jié)果相結(jié)合,最終將Rht-dp縮小在4BS基因組上的154766 751~250584 662區(qū)域,該區(qū)域具有約0.95億個(gè)堿基。與之前的SSR標(biāo)記結(jié)果相比,顯著性地縮小了0.55億個(gè)堿基位置。在該區(qū)域內(nèi)約有269個(gè)編碼基因(見表2),其中包含一個(gè)依賴S-腺苷-L-蛋氨酸的甲基轉(zhuǎn)移酶,該轉(zhuǎn)移酶是木質(zhì)素和異黃酮合成的關(guān)鍵限速酶[33]。阻礙S-腺苷-L-蛋氨酸的合成或者抑制S-腺苷-L-蛋氨酸甲基轉(zhuǎn)移酶均能導(dǎo)致植物的矮化[34-35]。因此,該基因可以作為Rht-dp的目標(biāo)候選基因,但有待于進(jìn)一步的驗(yàn)證。然而,由于Rht-dp的連鎖區(qū)域仍然較大,不利于目的基因的篩選。當(dāng)前中國春基因組參考序列版本(v1.0-assembly,2017年1月公布)的釋放以及目前候選區(qū)域的確定也將極大地利于其它分子標(biāo)記的開發(fā)和利用,從而進(jìn)一步縮小該區(qū)域并實(shí)現(xiàn)Rht-dp的精細(xì)定位和目的基因的克隆。目前,我們也正依據(jù)該目的區(qū)域內(nèi)參考基因組序列挖掘和設(shè)計(jì)了大量的SSR標(biāo)記并應(yīng)用于該重組自交系的驗(yàn)證,將Rht-dp的候選區(qū)域縮小到了0.1億個(gè)堿基區(qū)域內(nèi)(數(shù)據(jù)未發(fā)表),證實(shí)了利用SLAF-Seq-BSA關(guān)聯(lián)分析目標(biāo)性狀是切實(shí)可行的。
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Mapping of Rht-dp Derived from Dwarf Polish Wheat(Triticum polonicum)via SLAF-Seq-BSA
CHAI Song-yue,YAO Qin,CHENG Yi-ran,WANG Chao,ZHOU Yong-hong,WANG Yi*
(Triticeae Research Institute,Sichuan Agricultural University,Chengdu 611130,China)
【Objective】Fine mapping of Rht-dp derived from dwarf polish wheat(DPW).【Method】In this study,SLAF-Seq-BSA(specific-locus amplified fragment sequencing and bulked segregant analysis)was used to map the Rht-dp associated with dwarfism in DPW.【Results】Most of SLAF tags were evenly distributed in A and B genomes.However,a handful of tags were distributed in D genome or were not mapped on the genomes of Chinese Spring.Meanwhile,Rht-dp was mapped on the 4B genome started from 154766 751 to 343858 300.Combined with our previous SSR results,Rht-dp was finally mapped on the 4B genome started from 154766 751 to 250584 662.【Conclusion】All results indicated that there are some differences of genetic similarity between DPW and Chinese Spring.SLAF-Seq-BSA is an efficient strategy for mapping the Rht-dp,which would further help to fine map the Rht-dp by developing other new molecular markers,such as SSR marker.
dwarf polish wheat;SLAF-Seq;BSA;Rht-dp
S512.5
A
1000-2650(2017)04-0459-06
10.16036/j.issn.1000-2650.2017.04.001
2017-11-09
國家自然科學(xué)基金項(xiàng)目(31671688)。
柴松岳,碩士生。*責(zé)任作者:王益,副研究員,從事作物功能基因組學(xué)研究,E-mail:wangyi@sicau.edu.cn。
(本文審稿:武 晶;責(zé)任編輯:劉詩航;英文編輯:劉詩航)