BpSRK1-mediated phosphorylation of BpERF3 relieves HDA6-dependent chromatin repression to enhance drought tolerance in birch.

Drought tolerance in plants requires rapid conversion of water-deficit signals into protective transcriptional and epigenetic programs. Although ERF transcription factors (TFs) are central regulators of stress-responsive gene expression, how drought-induced kinase signaling is coupled to chromatin regulation and antioxidant gene activation remains unclear. Here, we identify the ERF TF BpERF3 as a phosphorylation-dependent regulator of drought tolerance in birch (Betula platyphylla). Using transgenic and CRISPR-Cas9 mutant lines, protein interaction assays, immunoaffinity fluorescent electrophoresis (IAFE)-based interactome mapping, post-translational modification analysis, reactive oxygen species measurements, and drought phenotyping, we dissected the regulatory mechanism underlying BpERF3-mediated stress adaptation. We show that BpERF3 activates the peroxidase (POD) genes BpPOD3 and BpPOD4, which are required for its drought-protective function. Mechanistically, BpSRK1 phosphorylates BpERF3 at Ser355, enabling phosphorylated BpERF3 to competitively engage the HDAC domain of BpHDA6 and restrict BpHDA6-dependent histone H3.1 deacetylation. Consequently, H3.1 acetylation is maintained, chromatin relaxes, downstream stress-responsive genes are activated, and drought tolerance is enhanced in birch. Our findings reveal a BpSRK1-BpERF3-BpHDA6-H3.1 regulatory module that links drought-induced phosphorylation to local chromatin activation and redox homeostasis, providing mechanistic insight into plant stress adaptation.