天然异源四倍体甘蓝型油菜中C基因组的重建及遗传分析

Allopolyploid derived from the interspecific hybridizations between related diploid ancestors is a vital way for speciation in nature, therefore, with some special genetic methods, the sustitution of the constituent subgenome(s) from a natural allopolyploid species of long history will provide an unique avenue to decipher the effects of long-term genome evolution and interplay. We extracted A genome and obtained a restituted Brassica rapa (RBR) from the allotetraploid oilseed rape (B. napus L., AACC) through inducing the preferential elimination of C-subgenome chromosomes in intertribal crosses, previously. In the present study, an auto-allohexaploid (AAAACC) was obtained via doubling the seedlings from the hybridization between restituted B. rapa and its parental B. napus. The constituted C-subgenome will be extracted and then restituted the progenitor of B. oleracea (restituted B. oleracea, RBO) in B. napus, through eliminating A-subgenome chromosomes due to the unstability of their multiple copies in meiosis. Then, transcriptomic and epigenetic analysis of RBR and RBO is performed to unravel the component subgenomes interplay of gene expression in B. napus, to explore the effects of co-evolution between A and C subgenomes and to give comprehensive insights into the evolution of allopolyploid.

由于种间杂交产生的异源多倍体物种经历了长期的进化过程，如能利用特定的遗传手段从天然异源多倍体中剥离出二倍体染色体组并对其进行重建，将为异源多倍化中基因组的遗传及互作研究提供独特的信息。我们前期通过族间杂交诱导甘蓝型油菜中C染色体组的特异性消除，剥离出A染色体组并重建白菜型油菜祖先种（restituted Brassica rapa, RBR）。本项目以RBR与亲本甘蓝型油菜杂交产生三倍体杂种（AAC），染色体加倍后获得同源异源六倍体（AAAACC）；处于四体状态的A染色体组在连续自交过程中不稳定而被消除，故剥离出C染色体组并获得重建型二倍体甘蓝（restituted B. oleracea, RBO）。随后进行RBR，RBO及甘蓝型油菜的基因表达分析，表观遗传变化分析，揭示甘蓝型油菜A、C基因组的基因表达与互作规律，为异源多倍体进化的遗传机制提供新知识。

异源四倍体甘蓝型油菜（Brassica napus, AnAnCnCn）是研究异源多倍体遗传进化的模式植物之一，其二倍体A、C基因组的基因表达与互作也一直是研究的重点。项目组通过对剥离白菜RBR（AnAn）进行基因表达及表观遗传分析，揭示部分基因响应甘蓝型油菜多倍化过程及其后续的人工驯化，同时发现约20%的差异基因反映A与C基因组的长期互作效应。同时项目组通过对RBR附加C染色体的全套附加系（AnAn+Cn1-9）的基因表达分析，证实C基因组染色体均会对A基因组的基因表达造成广泛的反式影响，并且原本表达水平比较高的基因，在A与C基因组互作过程中呈现低表达，低表达水平的基因则呈现高表达，这些基因表达结果可能体现了天然甘蓝型油菜中A与C基因组的共进化效应。此外，我们虽未从甘蓝型油菜同源异源六倍体（AnAnAnAnCnCn）中剥离出二倍体甘蓝，但证实该同源异源六倍体会进行快速的二倍化过程，并通过该同源异源六倍体创制出新的甘蓝型油菜种质资源。本项目为甘蓝型油菜的A、C基因组互作提供了新证据，并拓宽了甘蓝型油菜的种质资源。