Phosphorylation and epigenetic remodeling mediate BpEBP1-dependent drought resistance in birch.

Abstract

BpEBP1, an ethylene-responsive factor VII transcription factor, coordinates stress resilience in birch (Betula platyphylla), but its molecular mechanisms underlying drought response remain unclear. Using transgenic birch lines (overexpression and knockout), chromatin immunoprecipitation (ChIP)-seq, biochemical assays, and protein interaction studies, we dissected the multilayered regulatory network of BpEBP1. BpEBP1 enhances drought tolerance in birch by directly activating key lignin and anthocyanin biosynthesis genes (BpMYC2, BpCOMT, and BpPOD5), thereby promoting lignin deposition and anthocyanin accumulation, which reinforce cell wall rigidity and boost reactive oxygen species scavenging capacity. Beyond the canonical GCC-box cis-element, BpEBP1 binds to novel Noyes and ZNF449 motifs and uses these cis-elements to drive expression of the previously described target genes. Mechanistically, BpEBP1 recruits the histone demethylase BpJMJ25 to remove repressive H3K9me2 marks, thereby increasing chromatin accessibility to facilitate transcriptional activation. Meanwhile, drought-induced phosphorylation at Thr148 by BpEDR1 specifically increases the DNA-binding affinity of BpEBP1, without affecting its transactivation activity or interaction with BpJMJ25. BpEBP1 functions as a central regulatory hub that unites transcriptional activation of anthocyanin and lignin-related genes, BpJMJ25-mediated H3K9me2 epigenetic remodeling, and BpEDR1-dependent Thr148 phosphorylation. These two regulatory layers act independently yet synergistically, collectively activating drought-adaptive metabolic pathways and conferring robust drought resistance in birch.