一个新的水稻粒长基因qGL9的图位克隆与功能分析

Rice is one of the most important food crops. High yield and good grain quality are among the most important goals in rice basic research and breeding. Grain shape/size as specified by grain length, grain width, is a highly important yield trait and grain appearance quality trait. In recent years, a dozen of QTL genes for rice grain size have been isolated. However, our understanding of the molecular regulation mechanism of grain size is far from enough. In earlier stage of this research, we identified a novel quantitative trait locus (QTL) controlling grain length using a recombinant inbred line (RIL) population over 2 years. The QTL was located on chromosome 9 and was named qGL9. Near isogenic lines of qGL9 were constructed by continuous backcrossing selected RIL lines with the recurrent parent. The genetic effect of qGL9 on grain length was validated in a BC4F2 population, and the QTL was fine-mapped to a region of 348kb. qGL9 was further mapped to a 110kb region using a BC7F2 population. No genes related to grain size has been reported in this region. So we inferred that it was a new gene for grain length in rice. In this project, we focus on map-based cloning of qGL9, identifying the functional natural variation of qGL9 that controls grain length, and preliminarily exploring the molecular mechanism of how it regulates grain size. The rerults of the study will provide new perspective for molecular regulation of grain size and new gene resourse for genetic modification of rice.

水稻是重要的粮食作物之一，高产和优质是水稻基础科学研究和育种应用研究的重要目标。水稻粒型（可分解为粒长、粒宽和粒厚）是重要的产量性状和外观品质性状。目前已经克隆了数十个调控水稻粒型的数量性状位点（QTL），但粒型的分子调控网络还有待进一步研究。本项目前期利用一个重组自交系群体两年重复定位到一个位于第9染色体的控制粒长的QTL qGL9。通过回交构建了该位点的近等基因系，利用BC4F2分离群体验证了qGL9的遗传效应，并将其定位到348kb范围内。进一步利用BC7F2分离群体将qGL9定位到110kb范围内，该区域内不含有已经报道的粒型基因，qGL9是一个新的水稻粒长基因。本项目拟通过图位克隆的方法分离qGL9，鉴定并验证其功能性的自然变异，通过功能研究初步探索其调控种子大小的分子机理，加深对粒型分子调控机制的理解，同时，为水稻的遗传改良提供新的基因资源。

水稻是重要的粮食作物之一，高产和优质是水稻基础科学研究和育种应用研究的重要目标。水稻粒型（可分解为粒长、粒宽和粒厚）是重要的产量性状和外观品质性状。本项目前期利用一个重组自交系群体两年重复定位到一个位于第9染色体的控制粒长的QTL qGL9。通过回交构建了该位点的近等基因系，利用BC7F2分离群体将qGL9定位到110kb范围内。..进一步利用3000株的BC8F2分离群体将qGL9定位到6.0kb的区段内，含有2个ORF。比较亲本序列和候选基因在近等基因系幼穗中的表达量，将ORF1确定为qGL9的候选基因，ORF1编码一个Dof转录因子。在短粒近等基因系（NIL（BL130））背景下转入长粒型qGL9，粒长显著增加；在NIL（BL130）背景下超量表达qGL9，粒长也显著增加，以上结果表明该Dof基因是qGL9的功能基因，其正调控水稻粒长。对两等位基因启动子分段截短，利用双荧光素报告系统最终将导致qGL9表达量差异的功能性变异确定到翻译起始位点上游-540bp至-740bp区段内。近等基因系颖壳扫描电镜表明qGL9通过影响细胞大小来调控粒型。考察了NIL（J23B）和NIL（BL130）产量相关农艺性状，发现与NIL（BL130）相比，NIL（J23B）的粒长显著增加，粒宽显著降低，而千粒重无显著差异。NIL（J23B）的二次支梗数显著降低，致使每穗粒数显著降低，单株产量显著降低。在近等基因系间和转基因材料中都观察到植株松散程度的差异，考察茎节夹角大小，表明qGL9通过负调倒一和倒二茎节夹角来正调控植株直立程度。..本项目通过图位克隆的方法克隆了一个新的粒长QTL qGL9，编码一个Dof转录因子，其功能性自然变异很可能位于翻译起始位点上游-540bp至-740bp区段内。除了正调控粒长，qGL9还负调控穗粒数和正调控植株直立程度。本项目丰富了水稻粒型分子调控机制，也为水稻的遗传改良提供了新的基因资源。