玉米百粒重主效QTL ZmqKW3定位克隆及功能验证

Grain weight was highly correlated with yield in maize. To locate QTL/genes related to kernel weight and do the functional analysis could not only explain the genetic basis of grain weight, but also provide important gene resources and functional markers for the genetic improvement of maize grain weight traits. In the previous study, one major QTL ZmqKW3 was mapped on chromosome 3 about 1.3Mb range via chromosome segment substitution lines. The aims of this project are to do fine mapping again using one large population derived from QTL-NIL and genetic background Ye478. Combined with bioinformatics analysis, B73 genome sequence dada and expression analysis in diferent tissues and times, to screen and clone the key candidate gene controlling 100-kernel weight; to identify the gene function and develop functional markers via expression analysis, gene structure analysis and candidage gene association analysis. The genetic effects and breeding value in elite inbred lines will be done by BC-MAS method. The results of this study will get a new key gene affecting 100-kernel weight, not only conducive to the analysis of genetic mechanism of grain weight trait, but also provide effective markers and gene resource for genetic improvement of grain weight in maize.

玉米粒重与玉米产量高度正相关。开展粒重相关QTL/基因的定位克隆和功能分析，不仅可以解释粒重的遗传基础，也为玉米粒重的遗传改良提供重要基因资源和筛选标记。课题组前期工作中以染色体片段代换系为材料，将控制百粒重的主效QTL ZmqKW3定位在玉米第三染色体3.08bin约1.3M范围内。本项目拟利用QTL-NIL构建大的分离群体，进一步开展ZmqKW3精细定位。在此基础上，结合生物信息学、B73基因组序列数据和表达分析等方法，筛选并克隆控制百粒重的关键候选基因，分析基因结构及其时空表达模式。采用候选基因关联分析方法，验证基因功能，并开发功能标记；利用BC-MAS方法在优良自交系中分析ZmqKW3遗传效应及育种价值。本研究结果将获得一个新的影响百粒重的关键基因，不仅有利于玉米粒重性状遗传机制的解析，也为玉米百粒重性状的遗传改良提供有效标记及基因资源。

本研究图位克隆了一个新的控制玉米籽粒百粒重的主效QTL HKW3，并鉴定其关键候选基因ZmHB46，该基因编码Homeobox HD-ZIPⅡ类转录因子。进一步利用候选区段关联分析确定该基因启动子区是影响百粒重关键变异位点。为研究ZmHB46对籽粒粒重的影响，本研究首先对近等基因系间不同启动子进行激活活性验证，发现小粒系H15-6-2中520 bp左右的缺失影响了该基因的转录活性。对该基因的表达模式分析显示，不仅在分生组织SAM以及雌穗、雄穗中表达，而且在籽粒发育的糊粉层、胚旁细胞和胚中表达。接下来利用CRISPR/Cas9技术对该基因的启动子区和编码区进行敲除，对编码区敲除材料表型调查显示，该基因突变后影响雄穗和雌穗及籽粒的发育过程。通过转录组分析, ZmHB46影响NAC、GRF、EXPANSIN家族中多个基因的表达，这些基因家族在调控籽粒大小方面多有报道，说明ZmHB46可能是一个上游的转录因子，参与植物生长发育的基础过程。