Phosphorylation of RhoGDI1, a Rho GDP dissociation inhibitor, regulates root hair development in Arabidopsis under salt stress

Significance

Plants must actively regulate their growth to acclimate to stressful environments and optimize growth. Here, we describe a mechanism by which a root hair–specific response is important for salt tolerance in seedlings. We determined that SALT OVERLY SENSITIVE 2 (SOS2), a kinase that acts as a key master regulator in salt resistance, participates in root hair development under salt stress via a mechanism involving phosphorylation of (GUANOSINE NUCLEOTIDE DIPHOSPHATE DISSOCIATION INHIBITOR 1) RhoGDI1. We further demonstrated that the SOS2–RhoGDI1–ROP2 (SOS2–RhoGDI1–Rho GTPASE OF PLANTS 2) module regulates root hair initiation and growth to provide plant salt tolerance.

Abstract

To ensure optimal growth, plants actively regulate their growth and development based on environmental changes. Among these, salt stress significantly influences growth and yield. In this study, we demonstrate that the growth of root hairs of salt-stressed Arabidopsis thaliana seedlings is regulated by the SALT OVERLY SENSITIVE 2 (SOS2)–GUANOSINE NUCLEOTIDE DIPHOSPHATE DISSOCIATION INHIBITOR 1 (RhoGDI1)–Rho GTPASE OF PLANTS 2 (ROP2) module. We show here that the kinase SOS2 is activated by salt stress and subsequently phosphorylates RhoGDI1, a root hair regulator, thereby decreasing its stability. This change in RhoGDI1 abundance resulted in a fine-tuning of polar localization of ROP2 and root hair initiation followed by polar growth, demonstrating how SOS2-regulated root hair development is critical for plant growth under salt stress. Our results reveal how a tissue-specific response to salt stress balances the relationship of salt resistance and basic growth.