Division of Biological Sciences, Cell and Developmental Biology Section, University of California San Diego, La Jolla, CA, 92093, USA.
College of Resources and Environmental Sciences, National Academy of Agriculture Green Development, China Agricultural University, Beijing, PR China.
Nat Commun. 2020 Jan 2;11(1):12. doi: 10.1038/s41467-019-13875-y.
Abiotic stresses, including drought and salinity, trigger a complex osmotic-stress and abscisic acid (ABA) signal transduction network. The core ABA signalling components are snf1-related protein kinase2s (SnRK2s), which are activated by ABA-triggered inhibition of type-2C protein-phosphatases (PP2Cs). SnRK2 kinases are also activated by a rapid, largely unknown, ABA-independent osmotic-stress signalling pathway. Here, through a combination of a redundancy-circumventing genetic screen and biochemical analyses, we have identified functionally-redundant MAPKK-kinases (M3Ks) that are necessary for activation of SnRK2 kinases. These M3Ks phosphorylate a specific SnRK2/OST1 site, which is indispensable for ABA-induced reactivation of PP2C-dephosphorylated SnRK2 kinases. ABA-triggered SnRK2 activation, transcription factor phosphorylation and SLAC1 activation require these M3Ks in vitro and in plants. M3K triple knock-out plants show reduced ABA sensitivity and strongly impaired rapid osmotic-stress-induced SnRK2 activation. These findings demonstrate that this M3K clade is required for ABA- and osmotic-stress-activation of SnRK2 kinases, enabling robust ABA and osmotic stress signal transduction.
非生物胁迫，包括干旱和盐胁迫，会引发复杂的渗透胁迫和脱落酸（ABA）信号转导网络。ABA 信号转导的核心组分是 snf1 相关蛋白激酶 2（SnRK2s），它被 ABA 触发的 2C 型蛋白磷酸酶（PP2Cs）抑制所激活。SnRK2 激酶也被一种快速但大部分未知的非 ABA 依赖的渗透胁迫信号通路所激活。在这里，我们通过一个绕过基因冗余的遗传筛选和生化分析的组合，鉴定到了功能冗余的丝裂原活化蛋白激酶激酶（M3Ks），它们对于 SnRK2 激酶的激活是必需的。这些 M3Ks 磷酸化 SnRK2/OST1 上的一个特定位点，该位点对于 ABA 诱导的 PP2C 去磷酸化的 SnRK2 激酶的再激活是不可或缺的。ABA 触发的 SnRK2 激活、转录因子磷酸化和 SLAC1 激活在体外和植物中都需要这些 M3Ks。M3K 三重敲除植物表现出对 ABA 的敏感性降低和快速渗透胁迫诱导的 SnRK2 激活严重受损。这些发现表明，这个 M3K 类群对于 ABA 和渗透胁迫激活 SnRK2 激酶是必需的，从而能够实现稳健的 ABA 和渗透胁迫信号转导。
