稻属种间杂种不育基因S1等位变异与杂种不育的关系

The S1 locus in rice causes hybrid sterility and it is considered as the most important reproductive barrier between two rice species, Oryza sativa and Oryza glaberrima. Moreover, it is also detected through the crossing between O. sativa and the other AA genome relatives. Previous studies indicated that there existed different alleles at S1 locus by test cross and at least six different haplotypes existed in the AA genome species of genus Oryza based on the cloning study of S1 locus. The effect of allelic variation on the interspecific hybrid sterility is still unclear because of the difficulty to obtain the phenotype of the interaction among different haplotypes. In this study, we are going to sequence the S1 locus, including two genes, OgTPR1 and SSP, in AA genome relatives in order to identify the haplotype and raise near-isogenic lines. The hybrid combinations among NILs with different haplotypes will be obtained by incomplete diallel hybridization. The relationship between allelic variation and interspecific hybrid sterility can be detected by evaluating the pollen and spikelet fertility as well as the genetic behavior of gametes abortion in F1 and F2 generations. In addition, based on the sequence of S1 locus in non-AA genome and AA genome species, origin and evolution of S1 locus will be analyze in genus Oryza. This study will have the potential to understand the role of allelic variation of S1 locus in interspecific hybrid sterility among AA genome relatives. Meanwhile, this study can provide the evidence in breaking the interspecific hybrid sterility and understanding the evolution of genus Oryza.

S1是亚洲栽培稻与非洲栽培稻间最重要的种间杂种不育基因，且普遍存在于稻属AA基因组中。前期测交发现S1在稻属AA基因组中存在等位变异，S1基因克隆研究表明在稻属不同种中至少有6种单倍型，由于难以获得不同单倍型间互作的表现型结果，等位变异与杂种不育的关系尚不明确。本项目通过对稻属AA基因组8个种S1关键基因OgTPR1及SSP序列比对分析，鉴定S1位点的不同单倍型，培育不同单倍型S1近等基因系。进而采用双列杂交试验设计，分析S1基因不同单倍型近等基因系间互作与种间杂种F1、F2育性、配子消除作用的关系，最终明确S1不同等位变异在稻属AA基因组种间杂种不育的作用。同时对稻属AA基因组及非AA基因组S1基因序列进行分析，根据遗传分析和序列比对结果对S1在稻属中的演化进行推导。本研究有助于阐明S1在稻属AA基因组种间杂种不育的作用，并对打破稻属AA基因组种间生殖隔离及认识稻属种间分化提供理论依据。

本项目通过对稻属AA基因组8个种S1基因座3个关键基因A4,TPR,A6的序列比对分析，从稻属AA基因组8个种中鉴定到S1基因座的不同单倍型10个，基于不同单倍型培育相同背景下S1近等基因系35个。进而对10个代表了不同单倍型的近等基因系采用不完全双列杂交试验设计，获得45个杂交组合，通过分析这些杂交F1、F2花粉、小穗育性、配子败育情况研究S1基因不同单倍型间互作对种间杂种不育的效应。结果表明非洲栽培稻、巴蒂野生稻及长雄野生稻在S1基因座上均带有典型的“杀手”单倍型，这种单倍型对其余9种“非杀手”单倍型都有配子灭杀作用，但造成不育的程度不同。杀手单倍型之间不会发生配子灭杀，但“非杀手”单倍型间的互作会产生配子灭杀，以南方野生稻（Acc.104498）为代表的单倍型Allele3-3与尼瓦拉野生稻（Acc.100195）为代表的Allele4-2单倍型互作，Allele3-3单倍型的配子对Allele4-2的雌雄配子有灭杀作用，作用方式与杀手单倍型的相似。以上表明S1基因座在稻属AA基因组中分化成了不同的等位基因，不同等位基因间的互作应是稻属AA基因组各物种间杂种不育的本质。S1基因座序列比对结果表明，A4、TPR、A6三基因中，A4、A6在非AA基因组的稻族中并未检测到，说明A4、A6是形成稻属AA基因组种群之后演化而来的；TPR基因则较为保守，在稻属基因组中普遍存在，属于较古老的单倍型，其余9种“非杀手”单倍型是在“杀手”单倍型的基础上演化而成的，属于比较新的单倍型。另外，利用已培育近等基因系形成的分离群体检测到了与S1基因连锁的另一个杂种不育基因S5，S5是亚洲栽培稻籼粳亚种间最普遍的亚种间杂种不育基因，该结果证实了S5基因座存在于稻属AA基因组种间，为S5的分化早于籼粳亚种的分化这一观点提供了数据支持。上述研究结果为稻属AA基因组不同种间的杂种不育垂直同源基因，起源于共同的祖先，在漫长的历史演化过程中由于插入、缺失、突变、重组等形成了不同的单倍型，这些单倍型可能相互兼容，也可能产生杂种不育，杂种不育的产生进一步有了物种的分化这一推论提供了实证。