玉米GRAS家族蛋白ZmSCL1调控花粉淀粉积累的分子机制

The process of starch accumulation is a sign of pollen maturation, and it provides energy for the germination and growth of pollen tubes. The defects of starch accumulation may lead to a significant reduction of pollen vitality. Since, starch accumulation is a critical check point of pollen maturation, identifying the molecular mechanism regulating starch accumulation in pollen is of great theoretical significance. The GRAS family proteins are important transcriptional regulators in GA signal transduction and have diverse functions in plant growth, though the understanding of their roles in regulating starch accumulation in pollen grains is limited. Our previous study showed that ZmSCL1 expressed predominantly in pollen grains. Both ZmSCL1 Ac/Ds insertion mutant and its RNAi transgenic lines exhibited a reduced starch accumulation phenotype, suggesting that ZmSCL1 is critical for the starch metabolism in pollen. Besides, ZmSCL1 is localized in the nucleus, though it does not have transcription activation ability. This result indicates that ZmSCL1 may regulate downstream gene expressions by interacting with other transcription factors. In this proposal, we will investigate the physiological cause of pollen starch accumulation defects in the mutants and RNAi lines, and evaluate whether the pollen vitality was reduced. Moreover, we plan to screen interacting proteins of ZmSCL1 and identify its downstream genes. The prospective result of this research may provide molecular mechanism by which ZmSCL1 regulates starch accumulation in pollen, and explain the roles of GA signaling in pollen starch metabolism. In addition, our study may also provide putative approaches and gene resources for generating male-sterile lines of maize.

淀粉积累是花粉成熟的主要标志并且提供花粉管萌发和生长所需的能量，其积累缺陷会显著影响花粉活力。由于淀粉积累是花粉成熟的关键节点，因而对其调控机制的研究有重要意义。GRAS家族蛋白作为GA信号通路中的关键转录因子广泛参与植物生长发育调控，但对其在花粉淀粉积累中的功能仍未见报导。本项目前期发现GRAS家族蛋白ZmSCL1参与花粉淀粉蓄积调控，该基因主要在花粉中特异表达，其Ac/Ds突变体和RNAi株系花粉的淀粉积累均减弱。此外，ZmSCL1定位于细胞核且不具有转录激活活性，提示其可能通过蛋白互作调控下游基因表达。因此，本项目拟探明突变体中花粉淀粉积累受阻的成因及其对花粉活力的影响。通过筛选ZmSCL1互作蛋白和解析其下游基因表达调控网络，阐明ZmSCL1在花粉淀粉积累过程中的作用和调控机制。本研究对于解释GA信号在淀粉代谢中的作用具有重要意义，同时还可为玉米雄性不育调控提供新机制和基因资源。

淀粉积累是花粉成熟的主要标志并且提供花粉管萌发和生长所需的能量，然而花粉淀粉积累的分子调控机理仍不清楚。我们发现玉米GRAS家族蛋白ZmSCL1主要在花粉和籽粒中高表达，利用其突变体、RNAi、和过表达等遗传材料，结合生化和分子生物学等手段深入研究ZmSCL1在花粉淀粉积累和籽粒发育中的功能。研究发现ZmSCL1可通过与ZmMYB104、ZmRING1和ZmFBOX1等转录因子结合调控淀粉合成相关基因的表达，从而影响花粉淀粉积累。此外，籽粒灌浆关键调控因子Opaque2可在胚乳中激活ZmSCL1的表达，后者正向调控玉米籽粒的大小和重量，进而提出Opaque2-ZmSCL1模块介导协同胚乳增大与籽粒灌浆的机制。本研究全面阐释了ZmSCL1在调控花粉淀粉积累和籽粒增大中的分子机制，为更充分地理解ZmSCL1在不同组织器官中的功能差异提供依据，为探索“一因多效”的作用机理及具有多效性基因的生物技术育种应用提供重要支撑。在本项目的资助下，在Plant Physiology、JIPB、BMC Plant Biology等期刊发表（含接收）研究论文5篇，均已标注项目号（第一标注3篇），已培养博士生1名，硕士生1名，在读博士生1名。