Chromatin-Remodeling Factor CHR5 Promotes Defense Gene Expression and SA Accumulation

Chromatin remodelers play essential roles in modulating nucleosome structure and enabling dynamic transcriptional control. Arabidopsis calmodulin-binding transcription activators CAMTA1/2/3 negatively regulate plant immunity by suppressing the expression of biosynthesis genes of major defence hormones salicylic acid (SA) and N-hydroxy-pipecolic acid (NHP). The autoimmunity of the camta2/3 mutant is partially suppressed by loss of the NHP biosynthesis enzyme SAR deficient 4 (SARD4). During a forward genetic screen with the mildly autoimmune camta2/3 sard4 mutant, we identified chromatin-remodelling factor 5 (chr5) as its partial suppressor. The chr5 single mutants displayed decreased SA biosynthesis and compromised basal immunity. Further RNA-sequencing with chr5 defined immune-related genes that were downregulated in the mutants, including those involved in SA and NHP biosynthesis and signalling, PTI and ETI pathways. Our analysis highlights the roles of CHR5 in immune-specific chromatin remodelling events, contributing to transcriptional reprogramming during plant defence responses.