基于水稻染色体片段代换系的主效多粒密穗QTL-qSP1的图位克隆及分子机制研究

不管大穗型、穗粒兼顾型和多穗型哪种增产途径，解析其中基因是重要的课题。本研究创建了三片段水稻多粒密穗染色体片段代换系Z1364，并克隆了主效QTL-qSP1，qSP1编码转录辅抑制因子LEUNIG，遗传互补表明LEUNIG是目的基因。qSP1变异引起Z1364穗粒数显著增加。qRT-PCR分析表明，GN1a和其转录激活因子DST的表达在Z1364显著下调。GN1a表达下调会引起分生组织CK积累导致穗粒数增加，DST可以与GN1a启动子直接结合促进GN1a表达减少籽粒。本项目重点解决三个问题：以RNAi、超表达、原位杂交、亚细胞定位等明确qSP1的基本功能；以双、三突变体遗传分析qSP1与GN1a和DST调控关系；以ChIP、酵母双杂交、BiFC等明确qSP1靶基因和互作蛋白及调控水稻籽粒发育的分子机制。因而本项目对明晰qSP1调控水稻多粒密穗的机理及水稻大穗型新品种培育具有重要应用价值。

There are three types of increasing yield in production, including large-panicle type, both panicle and grain type, and multiple panicle type. Wherever by either type, it is an important subject to dissect key genes and revolve their molecular regulation mechanism. In our research, we identified a three-segment rice chromosome segment substitution line-Z1364 with increasing panicle grains from Nipponbare as recipient and Xihui18 as donor. And cloned the major QTL-qSP1 for increasing panicle grains which encodes LEUNIG, a transcriptional corepressor. Its mutation resulted in the increasing number of secondary branches, panicle grains and seed-setting density. qRT-PCR results showed that the expression levels of GN1a and DST which is the activator of transcription of GN1a were down-regulated significantly in Z1364 compared with Nipponbare. Based on the good research bases, three important problems will be resolved in the project. (1) Clarify the basic function of qSP1 by the methods as RNAi, over-expression, in situ hybridization, qRT-PCR, and subcellular localization, etc. (2) Clarify the regulating relationship of qSP1 and GN1a and DST by genetic analysis of double and triple-mutants. (3) Clarify the target gene and interaction protein by the methods as ChIP, EMSA, Yeast two-hybrid, BiFC etc. Consequently, the project will be of great value for explicating the molecular mechanisms of regulating grain development by qSP1 and for breeding novel rice varieties with large panicle type.