水稻 "杀手-保护者"生殖隔离体系的起源演化研究和在杂种优势上的应用

The hybrid sterility between the indica and japonica subspecies of Asian cultivated rice (Oryza sativa) is the best-characterized example of postzygotic reproductive isolation in plants. It is also a major barrier for utilization of the strong heterosis in inter-subspecific hybrids. S5 locus is a major locus conferring significant effect on hybrid fertility in indica-japonica crosses. Based on our previous work, a killer-protector system at the S5 locus was identified, which regulated fertility in indica-japonica hybrids by interactions between different alleles of three tightly linked genes. The origination and evolution of S5 system was accompanied with the occurrence of reproductive isolation. Therefore, understanding in the evolutionary process and divergence of S5 system provides insight in intrinsic mechanisms of evolution in multiple-interactive loci. Moreover, it also provides valuable clues for characterization of molecular and evolutionary mechanisms underlying reproductive isolation in plants. In this study, we plan to identify the origination time, the evolutionary steps, and establishment process of the S5 system in cultivated rice and its wild relatives. The evolutionary mechanisms underlying reproductive isolation will be investigated based on the evolutionary changes in S5 system. We also plan to investigate the primary functions of three genes in S5 system in ancient time by transformation and hybridization. The sequence and structure variations of the S5 system, as well as their effects in function divergence will be evaluated. In addition, we plan to investigate the divergence and evolutionary history of the regulatory network that the S5 system involved in, in order to unravel the driving force of such system during the evolution, as well as the intrinsic connection between natural selection, genetic variation, and reproductive isolation. Furthermore, we plan to screen for the wide-compatibility varieties at S5 locus based on the updated understandings, which may facilitate utilization of heterosis by overcoming indica-japonica hybrid sterility. These results will provide direct evidence in understanding the speciation in rice and evolutionary mechanisms underlying reproductive isolation, and they may also aid in rice genetic improvement.

水稻籼粳杂种不育是植物生殖隔离的代表实例，也是水稻杂交育种的主要障碍。S5位点是影响籼粳杂种育性的主效位点之一，前期工作发现该位点存在一个"杀手-保护者"互作体系，通过不同等位基因的互作引起杂种不育。S5体系的起源演化伴随着生殖隔离的产生，追溯其发生发展可揭示多基因互作的内在进化规律，也为理解植物生殖隔离的形成机制提供线索。 本研究（1）拟阐明S5体系的起源时间、建立顺序和产生机制，在此基础上阐明生殖隔离的发生机制。（2）拟鉴定三个基因的功能演变，以及序列变异和功能变化的联系。（3）拟研究S5体系所在调控网络的发生、演化和变异，并揭示其形成过程中进化的驱动力，自然选择、遗传变异和生殖隔离之间的关系和机制。（4）拟筛选S5位点广亲和品种，以S5为模式提出克服籼粳杂种不育的途径。 研究结果将增进对稻种起源演化和生殖隔离发生机制的理解，同时有助于亚种间杂种优势的利用，在理论和应用上都有重要意义。

亚洲栽培稻分为籼稻和粳稻两个亚种，亚种间杂种优势远大于亚种内的优势。籼粳稻亚种间普遍存在生殖隔离，导致亚种间杂种的育性下降，其强大的杂种优势难以利用。本研究对水稻杂种不育主效位点S5的起源演化规律进行研究，发现在稻族分化之后，该位点在Helitron转座子的介导下，由第五染色体三个连锁的母基因Ospara3-5复制所产生。在2个栽培稻种和11个野生稻种共计606份水稻中对S5位点进行基因型、核苷酸多态性以及单倍型分析，发现籼型等位基因为一次起源，而粳型等位基因经过两次突变产生，其基因型频率分别在自然选择和瓶颈效应的作用下上升，最终导致两个亚种间的生殖隔离。本研究还筛选出104份携带广亲和等位基因S5-n的水稻种质资源，这些材料与籼稻和粳稻在育性上表现出亲和性，可应用于水稻杂交育种和亚种间杂种优势利用。. 在上述对S5机制深入理解的基础上，本研究建立了广亲和分子育种体系，高效地将广亲和片段S5-n和f5-n精确导入籼稻品种9311。所获得的育种材料可提高33.6%~46.7%的杂种F1结实率。该研究建立的高效分子育种体系可为杂交育种提供有重要价值的育种材料。本研究亦创建了水稻已克隆基因和互作网络资源数据库，该数据库覆盖了水稻基因组19.2%的注释基因，释放以来被超过7000个不同的IP地址访问使用13500次以上，推进了水稻资源共享和遗传改良工作。. 本研究进一步在不同群体层面构建了水稻生殖隔离的遗传网络，通过对三个杂交组合的小穗育性、花粉育性和胚囊育性进行考察，基于超高密度遗传连锁图定位到43个杂种育性相关QTL和223对两位点互作位点，在全基因组层面阐明了籼粳亚种间以及籼籼亚种内杂种育性和生殖隔离的遗传机制，并鉴定了10个调控亚种间或亚种内杂种育性的新位点。研究结果表明不同类型的生殖隔离障碍具有截然不同的遗传与演化机制。.本研究从起源演化、杂种优势利用和遗传调控网络三个方面对杂种不育和生殖隔离的机制展开研究，研究结果对认识物种形成有重要理论价值，也为今后克服杂种不育和利用杂种优势提供了新的机遇。