提高水稻耐冷性是水稻育种的主要目标。OsMAPK3-OsbHLH002-OsTPP1信号通路增强水稻的耐冷性：该激酶被冷胁迫激活，随后转录因子被激活的激酶磷酸化，触发冷反应基因的表达。然而，这一通路是如何被及时抑制以避免其处于持续激活状态的，在很大程度上还是个未知数。
我们发现了一种新的2C蛋白磷酸酶OsPP2C27，它是OsMAPK3-OsbHLH002-OsTPP1通路的负调控因子。在低温处理过程中，OsMAPK3活性发生了动态变化。我们发现，在体外和体内，OsPP2C27与OsMAPK3发生物理相互作用，并使OsMAPK3去磷酸化。有趣的是，OsPP2C27还可以直接使OsMAPK3的靶标OsbHLH002去磷酸化。低温处理后，OsPP2C27-RNAi系和T-DNA插入突变体的存活率高于野生型，而OsPP2C27-高表达系的存活率低于野生型。
此外，OsPP2C27-RNAi细胞中OsTPP1和OsDREB的表达增加，而OsPP2C27过表达的细胞中OsTP1和OsDREB的表达降低。这些结果表明，低温诱导的OsPP2C27通过直接使磷酸化的OsMAPK3和磷酸化的OsbHLH002去磷酸化来负向调节OsMAPK3-OsbHLH002-OsTPP1信号通路，阻止了冷胁迫正向通路的持续激活，维持了低温条件下的正常生长。
Improving chilling tolerance is a major target of rice breeding. The OsMAPK3‐OsbHLH002‐OsTPP1 signaling pathway enhances chilling tolerance in rice: the kinase is activated by cold stress, and subsequently the transcription factor is phosphorylated by the activated kinase, triggering the expression of cold response genes. However, it is largely unknown how this pathway is suppressed in time to avoid it being in a continuously activated state. We found that a novel type 2C protein phosphatase, OsPP2C27, functions as a negative regulator of the OsMAPK3‐OsbHLH002‐OsTPP1 pathway. A dynamic change in OsMAPK3 activity was found during cold treatment. We show that OsPP2C27 interacts physically with and dephosphorylates OsMAPK3 in vitro and in vivo. Interestingly, OsPP2C27 can also directly dephosphorylate OsbHLH002, the target of OsMAPK3. After cold treatment, survival rates were higher in OsPP2C27‐RNAi lines and a T‐DNA insertion mutant, and lower in OsPP2C27‐overexpression lines, compared to wild type. Moreover, expression of the OsTPP1 and OsDREBs were increased in OsPP2C27‐RNAi lines and decreased in OsPP2C27‐overexpression lines. These results indicate that cold‐induced OsPP2C27 negatively regulates the OsMAPK3‐OsbHLH002‐OsTPP1 signaling pathway by directly dephosphorylating both phospho‐OsMAPK3 and phospho‐OsbHLH002, preventing the sustained activation of a positive pathway for cold stress and maintaining normal growth under chilling conditions.
Xia, C., Gong, Y., Chong, K. and Xu, Y. (2020), Phosphatase OsPP2C27 directly dephosphorylates OsMAPK3 and OsbHLH002 to negatively regulate cold tolerance in rice. Plant Cell Environ. Accepted Author Manuscript. doi:10.1111/pce.13938
