不同Km值的真菌谷氨酸脱氢酶（GDH）影响水稻碳、氮代谢平衡的机理研究

培育氮高效利用和高产水稻新品种对提高我国粮食产量和维持农业可持续发展非常重要。申请者前期研究创建了系列的真菌谷氨酸脱氢酶（GDH）转基因水稻材料，证实真菌GDH能改良水稻的氮同化效率。同时发现转基因水稻，当真菌GDH的Km（对NH4+）＜1.0 mM，生长量和产量显著降低；当1.0 mM＜Km＜3.0 mM，生长量和产量增加显著；当Km＞3.0 mM，生长量增强，产量增加不明显。在此基础上，提出不同Km值的GDH对生长量和谷物产量的影响源自其对水稻体内碳、氮代谢平衡的调控假说。本课题将以真菌GDH转基因水稻为材料，分析其在不同氮浓度处理下的生理生化指标，以及转录组和代谢组的变化，探明水稻体内碳、氮代谢平衡与水稻氮同化和谷物产量的内在关系，解析不同Km值的GDH影响水稻体内碳、氮代谢平衡的机理。该项目研究结果将为利用外源GDH培育氮高效利用和高产水稻提供重要的理论指导。

Breeding new high-yielding rice varieties with efficient use of nitrogen is very important for raising grain production and maintaining sustainable agriculture. We have created series of transgenic rice of fungus glutamate dehydrogenases (GDHs) with different Km values (affinity for NH4+). We confirm that fungus GDHs can improve the efficiency of nitrogen assimilation. Meanwhile, we find that in different Breeding new high-yielding rice varieties with efficient use of nitrogen is very important for raising grain production and maintaining sustainable agriculture. We have created series of transgenic rice of fungus glutamate dehydrogenases (GDHs) with different Km values (affinity for NH4+). We confirm that fungus GDHs can improve the efficiency of nitrogen assimilation. Meanwhile, we find that in different GDHs transgenic rice, the growth and grain yield decreased remarkably when Km ＜1.0 mM, while the growth and grain yield increased significantly when1.0 mM＜Km＜3.0 mM, and when Km＞3.0 mM, the rice growth enhanced but grain yield could not improve efficiently. Based on these work, we proposed a hypothesis that the effects of GDHs with different Km values on the phenotypes of transgenic rice derive from their impacts on the metabolic balance between carbon and nitrogen in rice. In this program, the fungus GDHs transgenic rice will be used as the experimental materials to be analyzed the physiological and biochemical characters, and transcriptome/metabolome profiles under different nitrogen concentration. We will investigate the inherent relationship among the carbon/nitrogen metabolism balance, nitrogen assimilation and grain production in rice. We would demonstrate the molecular mechanism under which fungus GDHs regulate the rice carbon/nitrogen metabolism balance. The research results may provide an effective theoretical guidance to breed the high-yielding rice varieties with efficient use of nitrogen by usages of exogenous GDH.