Guo Yazhen, Shi Yabo, Wang Yalin, Liu Fang, Li Zhen, Qi Junsheng, Wang Yi, Zhang Jingbo, Yang Shuhua, Wang Yu, Gong Zhizhong
State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Sciences, China Agricultural University, Beijing, 100193, China.
Center for Crop Functional Genomics and Molecular Breeding, China Agricultural University, Beijing, 100193, China.
New Phytol. 2023 Mar;237(5):1728-1744. doi: 10.1111/nph.18647. Epub 2022 Dec 16.
Drought is a major environmental stress that threatens crop production. Therefore, identification of genes involved in drought stress response is of vital importance to decipher the molecular mechanism of stress signal transduction and breed drought tolerance crops, especially for maize. Clade A PP2C phosphatases are core abscisic acid (ABA) signaling components, regulating ABA signal transduction and drought response. However, the roles of other clade PP2Cs in drought resistance remain largely unknown. Here, we discovered a clade F PP2C, ZmPP84, that negatively regulates drought tolerance by screening a transgenic overexpression maize library. Quantitative RT-PCR indicates that the transcription of ZmPP84 is suppressed by drought stress. We identified that ZmMEK1, a member of the MAPKK family, interacts with ZmPP84 by immunoprecipitation and mass spectrometry analysis. Additionally, we found that ZmPP84 can dephosphorylate ZmMEK1 and repress its kinase activity on the downstream substrate kinase ZmSIMK1, while ZmSIMK1 is able to phosphorylate S-type anion channel ZmSLAC1 at S146 and T520 in vitro. Mutations of S146 and T520 to phosphomimetic aspartate could activate ZmSLAC1 currents in Xenopus oocytes. Taken together, our study suggests that ZmPP84 is a negative regulator of drought stress response that inhibits stomatal closure through dephosphorylating ZmMEK1, thereby repressing ZmMEK1-ZmSIMK1 signaling pathway.
干旱是一种威胁作物产量的主要环境胁迫。因此，鉴定参与干旱胁迫响应的基因对于解析胁迫信号转导的分子机制以及培育耐旱作物至关重要，尤其是对于玉米而言。A类PP2C磷酸酶是核心脱落酸（ABA）信号传导组分，调控ABA信号转导和干旱响应。然而，其他PP2C亚家族在抗旱性中的作用仍 largely未知。在此，我们通过筛选转基因过表达玉米文库发现了一个F类PP2C，即ZmPP84，其负向调控耐旱性。定量RT-PCR表明ZmPP84的转录受干旱胁迫抑制。我们通过免疫沉淀和质谱分析鉴定出MAPKK家族成员ZmMEK1与ZmPP84相互作用。此外，我们发现ZmPP84可以使ZmMEK1去磷酸化并抑制其对下游底物激酶ZmSIMK1的激酶活性，而ZmSIMK1能够在体外将S型阴离子通道ZmSLAC1的S146和T520位点磷酸化。将S146和T520突变为模拟磷酸化的天冬氨酸可在非洲爪蟾卵母细胞中激活ZmSLAC1电流。综上所述，我们的研究表明ZmPP84是干旱胁迫响应的负调控因子，通过使ZmMEK1去磷酸化来抑制气孔关闭，从而抑制ZmMEK1-ZmSIMK1信号通路。
