Histone H2B N-tail mutation impairs innate immune gene regulation in Drosophila

Histones, traditionally known for roles in chromatin structure and transcriptional regulation, are increasingly recognized for their functions in immunity beyond the nucleus. This study investigates how single-residue substitutions in histone H2A/H2B affect innate immune competence in Drosophila melanogaster under physiological conditions. Using a systematic histone mutant library, we identified several alleles-particularly H2B K11A-that displayed significantly reduced survival following oral infection with Pseudomonas entomophila. Axenic rearing and 16S rRNA assays excluded microbial contamination, confirming the immune defect as mutation-intrinsic. RT-qPCR revealed that H2BK11A mutants exhibited markedly reduced basal expression of multiple antimicrobial peptide (AMP) genes, indicating impaired immune readiness. RNA-seq analysis further demonstrated widespread transcriptional repression, with innate immunity and defense-related genes, including key regulators (e.g., Mef2, tefu), being significantly downregulated. These findings provide in vivo evidence that specific histone N-tail residues are essential for maintaining immune gene networks in a multicellular organism.