Han, Ma, et al. reveal the mechanistic connection between shade avoidance responses and salt-induced responses.
Background: Sun-loving plants compete with their neighbors for sunlight by initiating shade avoidance syndrome (SAS). Phytochromes are plant photoreceptors that play a predominant role in perceiving the shaded environments and triggering SAS. Phytochrome-interacting factors (PIFs) are a subset of bHLH-family transcription factors that intrinsically promote plant growth. Upon light irradiation, photo-activated phytochrome B (phyB) interacts with PIFs via their active phytochrome B (APB)-binding motif and induces their rapid phosphorylation and degradation. Under shade, phyB is converted to the inactive form that cannot interact with PIFs; thus the abundance of PIFs is increased and plant growth is promoted.
Question: Are there any other factors that affect the phyB-PIF module in the shade?
Findings: We discovered that Salt Overly Sensitive2 (SOS2), a protein kinase essential for plant salt tolerance, positively regulates the response of Arabidopsis seedlings to shade. SOS2 directly phosphorylates PIF4 and PIF5 at a serine residue close to their conserved APB motif, thus decreasing the interactions of PIF4/PIF5 with phyB. Consequently, SOS2 post-translationally promotes PIF4 and PIF5 protein accumulation, and the role of SOS2 in regulating PIF4/PIF5 protein abundance and SAS is more prominent under salt stress. Moreover, we showed that phyA and phyB physically interact with SOS2 and promote SOS2 kinase activity in the light.
Next steps: We aim to explore how phytochrome photoreceptors mediate the synergistic enhancement of SOS2 kinase activity by shade and salt stress. In addition, we will investigate whether SOS2 is also involved in plant responses to other environmental stresses such as drought, cold, or heat stress.
Run Han, Liang Ma, Yang Lv, Lijuan Qi, Jing Peng, Hong Li, Yangyang Zhou, Pengyu Song, Jie Duan, Jianfang Li, Zhen Li, William Terzaghi, Yan Guo, Jigang Li (2023) SALT OVERLY SENSITIVE2 stabilizes phytochrome-interacting factors PIF4 and PIF5 to promote Arabidopsis shade avoidance. https://doi.org/10.1093/plcell/koad119