玉米粒型和灌浆关键基因的克隆与功能解析

In maize, kernel development is a continuous process that can be divided into three characteristic stages. The cells expand rapidly in number and size during the first stage, which determines the ‘storeroom’ for accumulation of photosynthate, and carbohydrates from leaf photosynthates are rapidly transported to the developing grain during the second stage, which accounts for the vast majority of kernel total dry matter,so the two stages dicide grain yield directly. To clone and elucidate the regulatory mechanism of the typical quantitatve genes controlling kernel size composed of kernel thickness, kernel length, and kernel width and grain weight is important for agricultural production practice. In pervious study, the candidate gene controlling kernel thickness (ZmCRP) have been cloned and validated, and two main QTL for kenerl length have been mapped. In this study, the two QTL for kernel length will be cloned and validated firstly, and the biological function and regulation network of the four genes during kernel development will be further dissected by transcriptome, yeast mating, co-immunoprecipitation, and cytology using the transgenic positive line and the control as a marterial. In addition, the favorable alleles and functional markers will be devoloped for MAS breeding and elite intermediate materials will be created by favorable gene pyramiding method for maize breeding.

玉米籽粒发育是一个连续的生物学过程，可以分为三个不同阶段，其中第一和第二阶段主要是籽粒细胞数目增加和光合产物的有效积累期，分别决定着籽粒体积（库）和重量（流），是影响玉米产量关键因素。由于籽粒体积和重量表现为典型的数量性状遗传，而籽粒体积又可以剖分为粒厚、粒长和粒宽等次级性状，因此对粒型性状的关键基因进行克隆，阐明其在籽粒发育过程中的代谢调控机制，对玉米育种具有重要指导意义。本研究拟在前期对玉米粒厚和产量候选基因ZmCRP进行克隆，以及对粒长主效QTL进行精细定位的基础上，克隆玉米粒长的两个主效QTL，通过遗传转化的方式对上述4个基因的功能进行验证，然后利用转录组学、酵母杂交、免疫共沉淀、细胞学等方法对转基因家系及其对照进行分析，解析候选基因的生物学功能和代谢调控网络，发掘优异等位基因和功能标记，利用基因聚合的方法创制优异的中间材料为育种服务。

在本基金的资助下，我们成功精细定位和克隆了玉米粒长两个主效QTL的候选基因，并对另外两个粒型基因进行了克隆和功能分析。通过对玉米籽粒粒长主效QTL进行精细定位及候选基因筛选克隆，以及对粒型基因SAS1和粒厚突变体基因dst1进行克隆与功能分析，来解析这些基因对玉米籽粒发育和灌浆进程的影响，以促进对玉米籽粒发育调控网络的研究。我们对玉米籽粒粒长主效QTLqKL9重定位，将其分解为qKL9-1和 qKL9-2两个主效QTL并进行精细定位，随后通过RNA-seq筛选候选区段差异表达基因，得到了ZmEXPB14和ZmEXPB15两个可能与粒型相关的候选基因，进行遗传转化；进一步研究发现粒型基因SAS1 编码一个P-type PPR蛋白，定位在线粒体，该蛋白突变使得多个线粒体编辑位点发生变化，影响线粒体正确的编码翻译，从而影响线粒体为维持正常细胞活动提供能量，导致籽粒缺陷；粒厚基因DST1编码一个C端具有Urb2结构域的核糖体生物合成相关蛋白，其结构域内的SNP22突变会导致rRNA加工紊乱和滞后，最终影响玉米的整体生长发育。研究结果有助于深入了解玉米籽粒灌浆和籽粒形成机制，可为选育灌浆速率快的玉米品种提供初步理论基础。