转录因子OsMADS23和OsMADS25调控水稻侧根发育及高盐胁迫应答的机理研究

Root system architecture is an important organ in plant. There are over 30 MADS-box transcript factors expressed in rice root, yet their biological functions for root development remain unknown. Previously we studied two root-specific MADS-box transcript factors OsMADS23 and OsMADS25, both of which have similar responses to hormones and abiotic stresses. More importantly, both OsMADS23 and OsMADS25 are involved in the lateral development in rice. Reverse genetics revealed that OsMADS25 controls the lateral root development via auxin signaling, and is also involved in response to high salinity stress. Here this proposal intends to investigate the mechanism for lateral root development and response to high salinity regulated by transcript factors OsMADS23 and OsMADS25 in rice. First, we will examine the interaction between OsMADS23 and OsMADS25, and their transcription activity by BiFC (bimolecular fluorescence complementation), CoIP (co-immunoprecipitation) and dual luciferase transcriptional activity assay. We will also further study biological functions of OsMADS23 and OsMADS25 by examining the lateral root development in osmads23, osmads25 and osmads23/25 by complementary experiments. This study will explore the crosstalk between auxin and ROS signaling, both of which might be involved in OsMADS23 and OsMADS25 controlling the lateral root development and responding to high salinity stress. The target genes regulated by both OsMADS23 and OsMADS25 under normal and high salinity conditions will be revealed by ChIP-seq (chromatin immunoprecipitation and sequencing) and EMSA (electrophoretic mobility shift assay) experiments. This proposed study will reveal the molecular mechanism by which OsMADS23 and OsMADS25 regulate the lateral root development and response to high salinity stress, and also provide basic foundations in improvement of rice root system development and response to abiotic stresses.

根系是植物的重要营养器官。水稻有30多个MADS-box转录因子在根部表达，但它们在根系发育中的功能还未得到验证。我们的研究表明，OsMADS23 和OsMADS25具有类似的组织表达及逆境响应模式，均参与水稻侧根发育；后者通过参与生长素信号调控水稻侧根发育，并参与高盐胁迫应答。本申请拟通过BiFC、CoIP等实验及双荧光素酶检测系统研究二者的互作及转录激活活性；通过osmads23、osmads25及osmads23/25单、双突变体及功能互补实验研究二者在水稻侧根发育及高盐响应中的功能；研究生长素信号和ROS信号在水稻侧根发育及其与环境信号交流过程中的互作，采用ChIP-Seq及EMSA实验研究二者在正常与高盐条件下共同调控的靶基因。本研究结果将揭示OsMADS23 和OsMADS25在水稻侧根发育及高盐胁迫应答胁中的功能及作用机理，为水稻根系改良及应对环境变化提供理论基础。

水稻是世界上最重要的粮食作物之一，也是单子叶植物的模式代表。健壮的、对生态环境适应性强的根系对于提高水稻产量具有重要意义。水稻有多个MADS-box转录因子在根部表达，但它们在根系发育中的功能还未得到验证。水稻根系特异性表达的MADS-box转录因子OsMADS23和OsMADS25参与高盐胁迫应答。本项目通过遗传学、生物化学和分子生物学的方法研究OsMADS23和OsMADS25在水稻侧根发育及高盐胁迫响应中的生物学功能，阐明二者调控水稻侧根发育及高盐胁迫响应的分子机制。该项目的重要研究结果如下：(1) OsMADS23能提高水稻在渗透胁迫条件下侧根的生长发育，并通过正向调控脱落酸（ABA）信号通路提高水稻的抗旱耐盐性。在高盐或干旱胁迫条件下，ABA信号通路的正向调控因子SAPK9与OsMADS23互作，并将其磷酸化，磷酸化的OsMADS23的转录激活活性提高，直接激活ABA合成酶基因OsNCED2， OsNCED3， OsNCED4及脯氨酸合成酶基因 OsP5CR的转录, 提高水稻体内ABA的水平及脯氨酸的含量，从而提高水稻的抗盐耐旱能力。(2) OsMADS25通过调节生长素（IAA）信号通路调控水稻侧根的发育。OsMADS25直接抑制IAA信号通路转录抑制子OsIAA14的转录，从而增强生长素信号的输出，即OsMADS25通过增强生长素信号输出调控水稻侧根发育。(3) OsMADS25通过正向调控ABA信号通路和活性氧的清除提高水稻的耐盐性。在高盐胁迫条件下，OsMADS25提高水稻ABA的合成，而且OsMADS25直接激活谷胱甘肽硫转移酶基因OsGST4及脯氨酸合成酶基因OsP5CR的转录，提高水稻对活性氧的清除能力及对细胞膜的保护能力，从而提高水稻在高盐胁迫条件下侧根的生长能力，提高其耐盐性。本项目的研究结果阐明OsMADS23和OsMADS25调控水稻侧根发育及高盐胁迫应答的分子机制，为水稻根系改良及应对环境变化提供理论基础。