Sending out an SOS: Interplay between salt stress and light signaling
Background: The Salt Overly Sensitive (SOS) pathway is evolutionarily conserved and essential for plant adaptation to salt stress. The protein kinase SOS2 functions as a network hub in the SOS pathway, and its kinase activity is rapidly activated by salt stress. Activated SOS2 then phosphorylates the Na+/H+ antiporter SOS1 at the plasma membrane, thereby activating SOS1 to extrude Na+ from the cytosol to the apoplast. Phytochromes (phyA and phyB) are the red and far-red light photoreceptors in plants and the PHYTOCHROME-INTERACTING FACTORS (PIFs) are bHLH-family transcription factors that negatively regulate photomorphogenesis. Upon light irradiation, photo-activated phytochromes interact with PIFs in the nucleus and induce their rapid phosphorylation and degradation, thus relieving their repressive effect on photomorphogenesis.
Question: How does the light signal modulate plants’ response to salt stress? Does nuclear SOS2 play a role in the salt stress response?
Findings: We show that t photo-activated phyA and phyB play important roles in promoting salt stress tolerance, contributing to enhanced salt tolerance of wild-type Arabidopsis seedlings in the light than in the dark. By contrast, PIFs function as the key negative regulators of plant response to salt stress. Moreover, SOS2 directly phosphorylates PIFs, thereby promoting their degradation via the 26S proteasome pathway in response to light. Interestingly, our data indicate that phyA and phyB physically interact with SOS2 and promote its kinase activity under light conditions. Together, our results uncover the molecular mechanism underlying the interplay between light and salt stress pathways that enables plants to acclimate to salt stress under light conditions.
Next steps: We aim to elucidate how photo-activated phyA and phyB promote SOS2 kinase activity. In addition, we will investigate the connections and contributions of cytosolic and nuclear SOS2 in regulating plant salt tolerance.
Reference:
Liang Ma, Run Han, Yongqing Yang, Xiangning Liu, Hong Li, Xiaoyun Zhao, Jianfang Li, Haiqi Fu, Yandan Huo, Liping Sun, Yan Yan, Hongyan Zhang, Zhen Li, Feng Tian, Jigang Li, and Yan Guo (2023). Phytochromes enhance SOS2-mediated PIF1 and PIF3 phosphorylation and degradation to promote Arabidopsis salt tolerance https://doi.org/10.1093/plcell/koad117
