zmSBP30基因调控玉米穗行数的分子机理研究

The identification and functional elucidation of genes controlling kernel row number (KRN) of maize ear is particularly helpful for dissecting the genetics basis and for guiding genetic improvement of grain yield of maize. Previous investigation in our laboratory indicates that a Insertion/Deletion (InDel) variation in promoter region and a single nucleotide polymorphisms (SNPs) in encoding region of zmSBP30 are significantly associated with KRN. RNA in situ hybridiization revealed that the zmSBP30 was abundantly accumulated surrounding on the base of both spikelet pairs meristems (SPMs) and spikelet meristems (SMs), presuming zmSBP30 plays an important role for regulating maize KRN by modulating initiation and maintenance of SPMs and SMs in female inflorescence of maize. In the project, we shall develop recombinants between promoter region and encoding region of zmSBP30 by backcrossing, and develop transgenic plant by CaMV 35S promoter-derived diverse alleles and RNAi of zmSBP30, to elucidate biological function of genetic variation in promoter region and encoding region, respectively. The Yeast-one hybrid, Yeast-two hybrid and Chromatin immunoprecipitation will be used to assay acting pathway of zmSBP30. The transcriptome of transgenic plant will be assayed to dissect the regulating network of zmSBP30. The genetic diversity in both teosinte collections and maize inbred line population, allelic expression and KRN phenotype in the progenies of teosinte × maize inbred will be assayed carefully to reveal the molecular evolution of the zmSBP30 during domestication and improvement of maize. Our objectives are to elucidate biological function and acting mechanism of zmSBP30 in regulation of KRN of maize ear.

控制玉米穗行数的重要基因鉴定及其作用机理研究对于解析玉米产量形成的遗传基础和指导产量性状的遗传改良具有重要的理论与实践意义。本课题组研究表明，zmSBP30基因启动子区的一个插入缺失变异和编码区的一个非同义突变位点与穗行数变异极显著关联；zmSBP30在幼穗中成对小穗分生组织（SPMs）和小穗分生组织(SMs)基部特异性表达，通过调节SPMs和SMs的起始与保持而控制穗行数的形成。本研究拟通过杂交驱动的基因重组、不同等位基因的遗传转化和RNAi，探明启动子和编码区变异的生物学功能；通过酵母单杂交、酵母双杂交和染色质免疫沉淀等解析该基因的作用途径；转基因植株的转录组分析研究该基因的调控网络。大刍草与玉米自交系中遗传变异的分析、大刍草与玉米自交系杂交后代的基因表达与表型分析，探讨该基因在玉米驯化和改良中的分子进化。通过以上研究以期阐明zmSBP30基因的功能以及调控穗行数形成的分子机理。

在该项目资助下，我们克隆了玉米穗行数相关基因ZmSBP30(UB3)，进一步研究揭示，UB3负调控穗行数。为解析UB3调控穗行数的分子机制，我们利用农杆菌介导的遗传转化，将miR156 靶位点突变的mUB3转化玉米和水稻，发现mUB3能强烈抑制玉米地上部分和地下部分的生长。高表达的mUB3也能抑制水稻的分蘖、花序分生组织的一级分支数和二级分枝数以及每穗籽粒数；适度表达的mUB3水稻植株，其分蘖和株高略微减少但花序一级分支和二级分支增加。我们分析了幼穗中UB3和其他三个SPL基因包括OsSPL7, OsSPL14 和 OsSPL17的表达水平，发现这3个基因在mUB3高表达的转基因植株中被下调表达，而在mUB3适度表达的植株中被上调表达。这些结果表明适度表达的UB3可以通过调节SPL基因的表达，进而促进穗部的分支。转录组分析、DNA-蛋白质结合分析和激素含量分析发现，UB3可直接调控细胞分裂素合成和信号途径的相关基因(LOG1,ARRs)以及参与花序发育的转录因子，从而调控分蘖和花序的发育。在玉米中，17个细胞分裂素合成相关的基因在突变体中上调表达，3个细胞分裂素降解途径相关的基因下调表达，其中，细胞分裂素-O-葡糖基转移酶、 AP2-EREBP，SBP29和MADS73的启动子区域有连续的2-3个GTAC motif, 能被UB3识别并特异性结合，表明UB3可以直接结合在这些基因的启动子区域。我们还发现，UB3可以直接结合在ZmFCP1和ZmWUS1的启动子区域，直接调控他们的表达。这一研究结果为利用UB3(ZmSBP30)改良水稻和玉米产量提高理论指导。