水稻籽粒蛋白质含量籼粳差异的遗传机制解析及关键基因挖掘

The genetic dissection of the mechanism underlying rice quality formation is the prerequisite for the improvement of rice quality. It is well known that protein content (PC) in milled rice not only directly determine rice nutrition quality, but also have a large effect on the eating and cooking quality, together with amylose content in endosperm. Thus, many efforts have been putting in the dissection of genetic mechanism underlying the PC variation, and a lot of QTLs were identified so far. Unfortunately, only one gene (OsAPP6/ qPC1) has been successfully cloned. However, why the PC in indica subspecies are higher than that in japonica ones? And how many genes/QTLs function in regulating the PC except for qPC-1 and qPC-10 identified in our previous work? There is little information accumulated about the genetic mechanism of on PC so far. Therefore, we plan to understand the genetic mechanism underlying PC variation in the following four aspects: (1) to explore the key genes/QTLs in rice natural population through genome-wide association analysis (GWAS); (2) to measure the transcriptional expression levels of genes encoding glutelin family in filling grains at 15 and 25 days after flowering in the natural rice population, and then to detect and analyze the eQTL and their effects on the PC variation by GWAS; (3) to choose 1-2 stable QTLs as the target for further fine-mapping and cloning. And (4), to introgress the cloned QTLs into cultivars through backcrossing for analysis of their potential in application in rice quality improvement. We believe the results obtained in this project will put insight on the genetic mechanism controlling PC variation in rice germplasm and will benefit us to improve rice quality in breeding practice.

水稻籽粒蛋白质含量不仅决定稻米营养品质，同时也是影响稻米蒸煮食味品质的关键因子。迄今为止，人们对水稻籽粒蛋白质含量的遗传研究大多集中在相关QTL的定位方面，仅成功克隆了1个相关基因（OsAPP6/qPC1）。然而，为何籼稻品种的蛋白质含量普遍高于粳稻？存在哪些关键基因控制籼粳亚种间蛋白质含量的差异？目前还不清楚。本项目拟围绕上述问题着重开展以下研究：（1）利用全基因组关联分析（GWAS）技术，以水稻籼粳亚种的自然群体为研究对象，挖掘控制蛋白质含量关键基因/QTLs；（2）在水稻自然群体中测定谷蛋白家族编码基因在花后15天和25天的表达量，分析相关eQTL及其与蛋白质含量变异的关系。（3）选择1-2个稳定遗传的QTLs进行精细定位与克隆。（4）通过回交转育，将克隆的QTL导入现有主栽品种，阐明这些关键基因的应用价值。本研究结果将为稻米品质的改良提供重要的依据和基因资源。

稻米蛋白质含量是水稻营养品质的重要影响因子，同时也显著影响稻米蒸煮食味品质。迄今为止，由于稻米蛋白质含量遗传机制的复杂性和对环境的敏感性，其遗传研究大多集中在QTL定位，很少能被精细定位或克隆。然而，为何籼稻品种的蛋白质含量普遍高于粳稻？存在哪些关键基因控制籼粳亚种间蛋白质含量的差异？至今不是很清楚。本项目首先利用CSSL群体在多环境下进行稻米蛋白质含量QTL鉴定，成功克隆了一个调控稻米蛋白质含量的关键基因OsGluA2。该基因在籼粳品种间启动子的序列差异影响基因表达水平并最终影响谷蛋白的积累，该基因是影响籼粳亚种蛋白质含量差异的关键基因；其次，本项目利用水稻种质资源为材料，对谷蛋白合成基因表达量进行了eGWAS分析和对稻米总蛋白及组分蛋白含量进行了GWAS分析，成功鉴定到了一系列重要位点，并进行了初步功能分析；最后，利用CRISPR/Cas9和MAS技术对稻米蛋白质遗传改良进行了初步探究。本研究结果为解析稻米蛋白质含量籼粳差异的遗传机制奠定了重要基础，也为稻米品质改良提供了重要的基因资源和分子生物学手段。