A DNA Methylation Reader–Chaperone Regulator–Transcription Factor Complex Activates <i>OsHKT1;5</i> Expression during Salinity Stress
Jie Wang, Nan Nan, Ning Li, Yutong Liu, Tianjing Wang, Inhwan Hwang, Liu B, Zheng‐Yi Xu
Abstract
Abstract Irrigated lands are increasingly salinized, which adversely affects agricultural productivity. To respond to high sodium (Na+) concentrations, plants harbor multiple Na+ transport systems. Rice (Oryza sativa) HIGH-AFFINITY POTASSIUM (K+) TRANSPORTER1;5 (OsHKT1;5), a Na+-selective transporter, maintains K+/Na+ homeostasis under salt stress. However, the mechanism regulating OsHKT1;5 expression remains unknown. Here, we present evidence that a protein complex consisting of rice BCL-2-ASSOCIATED ATHANOGENE4 (OsBAG4), OsMYB106, and OsSUVH7 regulates OsHKT1;5 expression in response to salt stress. We isolated a salt stress–sensitive mutant, osbag4-1, that showed significantly reduced OsHKT1;5 expression and reduced K+ and elevated Na+ levels in shoots. Using comparative interactomics, we isolate0d two OsBAG4-interacting proteins, OsMYB106 (a MYB transcription factor) and OsSUVH7 (a DNA methylation reader), that were crucial for OsHKT1;5 expression. OsMYB106 and OsSUVH7 bound to the MYB binding cis-element (MYBE) and the miniature inverted-repeat transposable element (MITE) upstream of the MYBE, respectively, in the OsHKT1;5 promoter. OsBAG4 functioned as a bridge between OsSUVH7 and OsMYB106 to facilitate OsMYB106 binding to the consensus MYBE in the OsHKT1;5 promoter, thereby activating the OsHKT1;5 expression. Elimination of the MITE or knockout of OsMYB106 or OsSUVH7 decreased OsHKT1;5 expression and increased salt sensitivity. Our findings reveal a transcriptional complex, consisting of a DNA methylation reader, a chaperone regulator, and a transcription factor, that collaboratively regulate OsHKT1;5 expression during salinity stress.