一个水稻半矮化新基因的图位克隆与功能分析

Plant height is crucial for rice yield. Large scale extension of semi-dwarf varieties has greatly improved rice yield, providing an effective support for world food security. Dwarf mutants are ideal materials for studying the regulatory mechanism of plant height in rice. Research on dwarf mutants provides a theoretical basis for the application of dwarf materials in breeding and production. In earlier stage of this research, we found a rice semi-dwarf mutant. Plant height of the mutant was about 70% of the wild-type.A significant difference of panicle length, grain nubmer per panicle, grain length/width/thickness and 1,000 grain weight of the mutant was also observed. Genetic analysis indicated that monofactorial recessive gene controlled semi-dwarf inheritance in the mutant. By extreme individual mapping method, we have restricted the candidate gene to about 135kb on rice chromosome 6. Gene predicting indicated no allele conflicts with any rice dwarf genes reported. So we inferred that it was a new gene conferring rice plant height. The project intends to separate the mutant gene via map-based cloning method and conduct systematic study of the function to clarify the mechanism of how it regulates rice plant height.

株高是影响水稻产量的关键因素之一，半矮化品种的推广极大地提高了水稻单产，为世界粮食安全提供了保障。矮化突变体是研究水稻株高调控机制的理想材料，对矮化突变体的研究可为矮化材料在育种和生产上的应用提供理论依据。本项目前期发现一个水稻半矮化突变体材料，株高约为野生型的70%，穗长、每穗粒数、粒长/宽/厚、千粒重相比野生型均有显著差异。遗传分析表明突变表型受隐性单基因控制。通过极端个体定位方法，已将该基因定位在水稻第六染色体135kb范围内。基因预测表明区域内基因与已报道的水稻株高基因不等位，是一个新的水稻矮杆基因。本项目拟通过图位克隆的方法分离该突变基因，并对其功能进行较为系统的研究，探索其对水稻株高的调控机理。

株高是影响水稻产量的关键因素之一，半矮化品种的推广极大提高了水稻单产，为世界粮食安全提供了重要保障。本研究从一个水稻半矮化突变体材料入手，通过图位克隆获得了控制株高的新基因RTD1。基因突变后引起水稻株高变矮、单株穗数、每穗粒数、穗长、粒长/宽/厚、千粒重、结实率等重要农艺性状值均降低。RTD1编码尿黑酸植基转移酶，是生育酚（维生素E）生物合成途径中的关键节点基因，rtd1突变体中检测不到生育酚的合成。RTD1基因在水稻中呈组成型表达，但在绿色部位高表达，蛋白的亚细胞定位在叶绿体中。进一步的研究表明，与野生型日本晴相比，rtd1突变体的耐寒性极显著降低，且在自然生长条件下与冷胁迫密切相关的CBF/DREB1基因表达量显著上调。此外，突变体对赤霉素的敏感性降低，赤霉素信号途径中的抑制因子DELLA蛋白SLR1在转录和蛋白水平上都表现上调，部分解释了突变体整体生长发育下降的原因。但突变体中赤霉素含量与野生型相比没有发生变化，表明SLR1蛋白的过度积累是由于基因的转录上调引起，而非翻译后蛋白被赤霉素降解的减少引起。本研究揭示了生育酚作为一种生物抗氧化剂对水稻的生长发育起重要作用。