MOA Key Laboratory of Crop Ecophysiology and Farming System in the Middle Reaches of the Yangtze River, Huazhong Agricultural University, Wuhan 430070, China.
College of Plant Science and Technology, Huazhong Agricultural University, Wuhan 430070, China.
J Exp Bot. 2021 Sep 30;72(18):6611-6627. doi: 10.1093/jxb/erab287.
Ca2+/calmodulin (CaM)-dependent protein kinases (CCaMKs) and mitogen-activated protein kinase kinases (MAPKKs) are two types of kinases that regulate salt stress response in plants. It remains unclear, however, how they cooperatively affect lateral root growth under salt stress. Here, two conserved phosphorylation sites (S102 and T118) of OsCaM1 were identified, and found to affect the ability to bind to Ca2+in vitro and the kinase activity of OsCCaMK in vivo. OsCCaMK specifically interacted with OsMKK1/6 in a Ca2+/CaM-dependent manner. In vitro kinase and in vivo dual-luciferase assays revealed that OsCCaMK phosphorylated OsMKK6 while OsMKK1 phosphorylated OsCCaMK. Overexpression and antisense-RNA repression expression of OsCaM1-1, and CRISPR/Cas9-mediated gene editing mutations of OsMKK1, OsMKK6, and OsMKK1/6 proved that OsCaM1-1, OsMKK1, and OsMKK6 enhanced the auxin content in roots and lateral root growth under salt stress. Consistently, OsCaM1-1, OsMKK1, and OsMKK6 regulated the transcript levels of the genes of this cascade, and salt stress-related and lateral root growth-related auxin signaling under salt stress in rice roots. These findings demonstrate that the OsCaM1-associated OsCCaMK-OsMKK1/6 cascade plays a critical role in recruiting auxin signaling in rice roots. These results also provide new insight into the regulatory mechanism of the CaM-mediated phosphorylation relay cascade to auxin signaling in lateral root growth under salt stress in plants.
钙调素（CaM）依赖的蛋白激酶（CCaMKs）和丝裂原活化蛋白激酶激酶（MAPKKs）是两种调节植物盐胁迫反应的激酶。然而，它们如何协同影响盐胁迫下侧根的生长尚不清楚。本研究鉴定了 OsCaM1 的两个保守磷酸化位点（S102 和 T118），发现它们影响体外与 Ca2+结合的能力和体内 OsCCaMK 的激酶活性。OsCCaMK 以 Ca2+/CaM 依赖的方式与 OsMKK1/6 特异性相互作用。体外激酶和体内双荧光素酶测定显示，OsCCaMK 磷酸化 OsMKK6，而 OsMKK1 磷酸化 OsCCaMK。OsCaM1-1 的过表达和反义 RNA 抑制表达，以及 OsMKK1、OsMKK6 和 OsMKK1/6 的 CRISPR/Cas9 介导的基因编辑突变证实，OsCaM1-1、OsMKK1 和 OsMKK6 增强了盐胁迫下根和侧根生长中的生长素含量。一致地，OsCaM1-1、OsMKK1 和 OsMKK6 调节了该级联反应的基因的转录水平，以及盐胁迫下水稻根系中与盐胁迫和侧根生长相关的生长素信号。这些发现表明，OsCaM1 相关的 OsCCaMK-OsMKK1/6 级联在招募水稻根系中生长素信号中起关键作用。这些结果还为 CaM 介导的磷酸化传递级联调节植物盐胁迫下侧根生长中生长素信号的机制提供了新的见解。
