基因可变剪接参与拟南芥生态型间杂交不亲合调控研究

It has long been known that species or subspecies hybrids, even when they are able to form, often fail owing to sterility, adult inferiority, or embryonic lethality, thus preventing gene flow among species or subspecies and leading to reproductive barriers and speciation. Assessing the phenomenon and underlying mechanism of hybrid incompatibility (HI) are critical for understanding microevolution. In the Dobzhansky-Muller model, two or more DM genes control HI via a negative interaction. Thus far, more than a dozen DM genes have been isolated from model animals and plants; however, little is known about the mechanism mediating HI. We previously showed that SKIP and HIC1 are novel DM genes in Arabidopsis thaliana accessions. We also demonstrated that natural variations in HIC1 determined HI, while an SNP in HIC1 affected the SKIP-mediated alternative splicing of HIC1 pre-mRNA in these accessions. The proposed work will use SKIP/HIC1-mediated HI in Arabidopsis thaliana accessions as a model system to further reveal the mechanism of HI, with the hope of establishing alternative gene splicing as a mechanism of Dobzhansky-Muller-type HI and a critical regulatory step in microevolution. Therefore, the results from the proposed work will provide new insight into our understanding of microevolution.

生物种间或亚种间杂交往往会导致杂交不亲合，并进一步导致基因在种间或亚种间流动障碍, 最终会导致生殖隔离和新物种的产生。对杂交不亲合现象以及机制的研究对于认识生物微进化的机制有重要意义。杂交不亲合一般由两个或两个以上Dobzhansky-Muller(DM)基因控制，近年来科学家已经从果蝇、线虫以及拟南芥和水稻等物种中鉴定到多个DM基因，但对调控杂交不亲合的机制了解甚少。我们前期的工作表明SKIP和HIC1是控制拟南芥生态型间杂交不亲合的两个新的DM基因，并有初步结果表明拟南芥生态型间HIC1基因的SNP差异决定生态型间杂交亲合与否，HIC1的SNP差异影响SKIP对HIC1前体mRNA的可变剪接。该项申请将在上述结果基础上，以SKIP和HIC1两个基因相互作用调控拟南芥生态型间杂交不亲合为切入点，拟揭示基因可变剪接是控制生物种内杂交不亲合的一种新机制，从而揭示和丰富生物微进化的分子机制。

不同物种或亚种间通过杂交得到的后代相对于亲本可能在营养生长阶段表现出杂交优势，但在生殖阶段表现出缺陷，或在生长发育或环境适应的各方面均表现出劣势。这种杂交后代相较于亲本出现劣势的现象称之为种间或亚种间的合子后杂交不亲和。亲和性作为物种演化和形成的生物学基础，决定和平衡了物种的多样性和稳定性，因此解析控制物种种间和亚种间杂交不亲和的分子机制是生物学研究的重要问题之一。杂交不亲和现象的理论遗传机制可通过Dobzhansky-Muller(DM)模型解释，两亲本原始遗传位点在演化过程中由于遗传变异的积累导致功能出现分化，在杂交后的重组遗传背景下，两个或两个以上遗传位点（DM基因）之间出现不匹配，产生有害相互作用进而导致杂交不亲和。本项目鉴定到两个新的DM基因，并发现SKIP和HIKI1的有害上位性互作会导致拟南芥生态型间杂交后的出现重组合子败育、雄配子体传递效率降低、SKIP位点偏分离的杂交不亲和现象，其分子机制是SKIP通过直接结合HIKI1的pre-mRNA调控其剪接，当SKIP剪接活性下降时，HIKI1的SNP4G会导致HIKI1出现内含子保留，触发拟南芥生态型间的杂交不亲和，即受SKIP调控的HIKI1可变剪接是导致拟南芥生态型间杂交不亲和的一个原初反应。综合上述结果证实基因转录后可变剪接是调控拟南芥生态型间杂交不亲和的一种新分子机制。