水稻结实率杂种优势负向超显性位点的功能研究与利用

As a major determinant of grains per panicle, decrease in seed setting rate affects yield in hybrids significantly. The loci showing negative overdominance in heterosis for fertility lead to reduced seed setting rate in heterozygote relative to its parents, which provide insight into yield improvement and mechanisms with respect to heterosis.. Previously, we have constructed an immortalized F2 population, an F2 population, and reciprocal introgressive lines derived from the cross between Zhenshan 97 and Minghui 63. Based on data of hybrid spikelet fertility from three replicated field trials and the corresponding ultra-high density genetic maps, significant negative overdominance effects were detected in 51 bins, leading to reduced fertility in hybrids. Therefore, there is still room for improvement in seed setting rate of Shanyou 63.. In this study, we plan to fine map three loci exhibiting negative overdominance in hybrid fertility, regulating pollen and embryo-sac development, respectively, both of which are repeatedly detected in field experiments. Genetic effect and functional characterization of the three loci in hybrid seed setting will be investigated, in order to determine the mechanism regulating heterosis for fertility. In addition, we plan to investigate natural variations of these identified loci and their values in genetic improvement in hybrid fertility, on the basis of 606 rice materials and 16 constructed F2 populations. These results will provide direct evidence in understanding the biological mechanisms underlying hybrid sterility and hybrid vigor, and they may also aid in heterosis breeding and improving seed setting rate in hybrids theoretically and practically.

结实率是每穗实粒数的重要组分，对杂交稻产量有直接影响。结实率杂种优势的负向超显性位点导致杂合子结实率低于亲本，其功能解析为阐明杂种优势机制和进一步提高杂交稻产量提供切入点。前期工作创建了珍汕97×明恢63永久F2、F2群体和双向导入系，基于三年田间结实率数据和对应超高密度遗传连锁图，在51个遗传bin中检测到负向超显性效应，导致杂种育性降低，也说明杂交稻汕优63的结实率还有提高空间。本研究以三次田间试验重复鉴定到的三个负向超显性位点为研究对象，将其效应分解为花粉和胚囊育性，克隆并解析其遗传效应和杂合背景下的功能，阐明其调控结实率杂种优势的机制。在此基础上利用606份水稻种质和已构建的16个F2群体鉴定三个位点的育种价值，评价优良等位基因和单倍型组合在杂交稻结实率性状改良中的潜力。研究结果将增进对杂种不育和杂种优势机制的理解，同时为杂交育种和提高水稻产量开拓思路，在理论和应用上有重要意义。

杂交稻为提高我国水稻产量做出了巨大贡献，解析杂交稻产量的调控机制不仅面向我国粮食安全的重大需求，也瞄准了生物学领域的重要科学问题。杂交稻的产量作为一个复杂性状，可以进一步分解为产量三要素，即每穗实粒数、粒重、有效穗数；其中每穗实粒数很大程度受结实率的影响。. 本研究对杂交稻结实率的遗传和分子机制进行了解析。利用9个水稻杂交群体系统剖析了杂种结实率和偏分离的遗传调控网络，在全基因组层面定位到61个偏分离位点，包括24个调控杂种后代偏分离的新位点，其中73%的偏分离位点在不同杂交群体重复检测到。第3、第6和第12染色体是偏分离发生的热点区域，分别对应于水稻杂种结实率位点Sc、S5和pf12/qS12。分析发现杂种结实率位点的遗传模型可以由平行演化模型、次第演化模型、平行-次第演化模型三种模式来解释。其中S1位点和S5位点的互作模式和起源演化均符合平行-次第演化模型。在S1位点，杀手-护卫平衡的建立是导致杂种不育的原因。与之相反，在S5位点，杀手-护卫平衡的打破将导致杂交稻的结实率下降。在此基础上，进一步在珍汕97×明恢63杂交群体中，对调控杂种花粉发育的新位点NO1进行了克隆和遗传效应分析。针对杂交稻产量三要素的粒重表型，本研究发现G蛋白α、β和γ亚基共同参与粒重和粒形的遗传调控。同时，三个Gγ蛋白通过协同互作和反馈调控，可实现水稻粒重从降低40%到增加28%的精准调控，从而提高水稻的产量。同时也创建了水稻功能基因应用数据库和相关分析工具，服务于杂交稻的遗传改良。. 本研究以提高杂交稻产量、推进水稻杂种优势利用效率为目标，针对杂交稻结实率和粒重两个性状展开研究，研究结果增进了杂交稻产量调控机制的认识，同时也为水稻杂种优势利用提供了新的基因资源和应用工具。