拟南芥多倍体减数分裂同源重组频率的分子调控机制解析

Meiosis including homologous chromosome pairing, synapsis, recombination, and segregation, is the crucial process in eukaryotic sexual reproduction, which not only guarantees the constant chromosome number in plant species, also is the important source of genetic diversity. Although many genes participating in meiosis have been found so far, considering the complex regulation network involved, the mechanism regulating meiotic homologous recombination is still unclear. Previously, our studies have confirmed that compared with diploid, polyploid Arabidopsis gave rise to increased recombination frequency during meiosis, and accordingly the expression level of involved genes was also significantly upregulated. Based on these results, transcriptome analysis is used to reveal regulation network of differential expressed genes during meiosis in polyploid Arabidopsis in comparison with diploids, and novel key genes potentially involved in meiosis is to be clarified as well, which would contribute to reveal gene- regulating network involved in homologous recombination during meiosis in polyploid Arabidopsis. Meanwhile, we also propose to study molecular function on recombination frequency exerted by some key meiosis-specific genes including atspo11-1 (inducing DNA double-stranded breaks, atasy1 (homologous synapsis) and atdmc1 (recombination repair) using RNAi and overexpresssion in polyploid Arabidopsis to reveal their biological roles in homologous recombination. Therefore, the present work would theoretically be of great significance and contribute to explanation of evolutionary dominance of polyploidy and genetic diversity in flowering plants.

减数分裂包括同源染色体配对、联会、重组、分离等过程，是真核生物有性生殖的核心事件，不但保证了物种染色体数目的恒定，也是遗传多样性产生的重要源泉。尽管许多参与减数分裂的基因已被克隆, 但由于复杂的调控网络，减数分裂同源重组的机理仍不太清楚。我们前期研究已证实，与二倍体相比，拟南芥多倍体减数分裂同源重组频率显著提高，且其调控基因表达也增强。本项目在此基础上，引入转录组学研究策略，分析拟南芥多倍体减数分裂调控同源联会与重组的差异基因网络图谱，明确参与调控的关键基因，以深度解析拟南芥多倍体减数分裂调控同源联会与重组的网络机制。同时，利用转基因分析参与诱导DNA双链缺口、同源联会和重组修复等关键基因的过量表达及沉默对拟南芥多倍体同源重组频率的影响，明确其调控的生物学功能，进而阐明拟南芥多倍体同源重组频率提高的分子遗传机理。本项目研究结果对深入阐释多倍体植物进化的主导地位及遗传多样性具有重要理论意义。

减数分裂包括同源染色体配对、联会、重组、分离等过程，是真核生物有性生殖的核心事件，不但保证了物种染色体数目的恒定，也是遗传多样性产生的重要源泉。本研究以拟南芥（白菜）二倍体和四倍体为研究对象，首先解析了多倍体对基因组结构改变（或变异）的影响，研究结果表明，与拟南芥二倍体野生型相比，同源多倍化导致基因组结构发生明显改变（或变异），三倍体基因组结构改变（或变异）程度大于同源四倍体，这些结构改变的位点可以发生在基因间隔区和基因内部，并影响基因的转录和表达。此外，与拟南芥四倍体野生型相比，四倍体RNAi突变体（ SPO11-1 、PRD1、DMC1）基因组结构改变（变异）水平有所下降，表明多倍体可 能会对基因突变造成的的基因组结构变异产生一定的缓冲作用。细胞遗传学研究表明，多倍体减 数分裂过程均出现异常，中期I出现多价和单价体，后期I和后期II染色体不均等分离。转录组谱分析发现，DMC1是减数分裂特异基因，参与DNA缺 口断裂的修复和同源重组，在四倍体中显著下调，很可能是导致多倍体减数分裂 出现异常的重要原因。此外，一些参与同源重组， 剪接体装配和碱基切除过程的基因在四倍体中也发生一定程度的改变。蛋白质组学分析进一步表明，四倍体中与“细胞周期调控“，“细胞骨架”、“染色质结构及动力”相关的差异蛋白均明显上调表达，而涉及修复重组途径 的差异蛋白显著下调表达，尤其是，参与减数分裂期碱基修复的PARP1和LIG1以及涉及重组修复的蛋白BARD1在四倍体中显著下调表达，表明同源四倍体减数分裂期DNA的修复途 径可能受到一定程度的影响。通过对雌雄配子早期发育过程的基因表达谱分析，与雄配子相比，重组修复基因表达量在雌配子相对较高，在发生生殖细胞DNA损伤后，雌配子体具有较强的的DNA损伤修复能力，相同条件下，雄配子更容易发生突变而导致遗传多样性。