油菜进化过程中A9染色体的结构变化

psRapeseed consists of three species Brassica rapa,B. juncea and B. napus, among which B. napus and B. juncea are allotetraploids derived from interspecific hybridization between B. rapa and B. oleracea or B. nigra.After formation of these allotetraploid species,various subspecies are produced through selection during domestication and breeding. What structual variation did chromosomes of B. juncea and B.napus experience on allopolyploidization? Did B. juncea and B. napus undergo the same chromsomal variation in structure although they have different genomic constitutions? What structural variation were brought about by selection during domestication and breeding? When and Which portion of a chromosome did these variations occur? To address these issues, the chromosome A9 is taken as an model for investigation by construcion of contigs and sequencing of B. juncea A9, comaprison of the aligned A9 chromsome nucleotide sequences from B. juncea, B.napus and B.rapa and association analysis of the genes for major agronomic characters.These investigations will not only uncover structural variation of Brassica A9 chromosome through evolution,but also show the genes this chromosome carries in various subspecies or even varietal groups,which will provide a theoretical foundation,gene resource and selection procedure for breeding.

油菜有白菜型、甘蓝型和芥菜型三类，其中甘蓝型和芥菜型油菜分别是白菜型油菜（白菜）与甘蓝、黑芥杂交形成的异源四倍体，它们形成之后由于选择、育种的作用各自又分化成多个亚种。在多倍化时，甘蓝型和芥菜型油菜中来自于白菜型油菜的染色体发生了哪些结构变化，不同基因组组成的芥菜型油菜与甘蓝型油菜这些染色体是否发生了相同的结构变化？在多倍化后，由于驯化选择和育种，又使得染色体在结构上发生了哪些变化？这些变化在何时、什么位置发生？围绕着上述问题，本项目将以A基因组最长的染色体A9为例，通过构建芥菜型油菜A9染色体BAC重叠群和测序、三类油菜A9染色体序列拼装比较和主要农艺性状基因关联分析进行研究。本研究不仅能阐释三类油菜A9染色体在进化不同阶段发生的结构变异，而且能揭示油菜不同类型、品种A9染色体的基因组成及其控制的性状，为育种提供理论依据、基因资源和选择方法。

异源多倍化是植物中常见的现象，异源多倍化过程中对基因组的结构会产生影响。本项目以共同具有A基因组异源四倍体芥菜型油菜（Brassica juncea）和甘蓝型油菜（B.napus）为对象，选择A基因组最长的染色体A9作为代表，比较其与祖先种白菜（B. rapa）的结构变化。通过超高密度遗传图谱构建、BAC重叠群构建和基因组测序分析，估计芥菜型油菜基因组大小为874Mb，A9染色体超高密度遗传连锁图谱含有15543个标记长1526.8cM，物理图含20个BAC重叠群474个BACs，组装序列49.817Mb。参与国际合作完成甘蓝型油菜全基因组测序并进行4个品种重测序，发现甘蓝型油菜品种间存在大量结构变异。从图谱和序列不同层次比较芥菜型油菜、甘蓝型油菜与白菜A9染色体的结构，发现在异源多倍化过程中着丝粒区域发生了结构改变，尽管芥菜型油菜与甘蓝型油菜多倍化过程中这种结构变化不相同，说明受到远缘杂种基因组组成的影响。此外，克隆了A9染色体控制原花色素合成和油脂积累的10余个基因。这些研究结果为进一步研究油菜进化奠定了基础，也为能揭示油菜不同类型、品种A9染色体的基因组成及其控制的性状，为育种提供理论依据、基因资源和选择方法。