Genome-wide shifts in histone modifications at early stage of rice infection with Meloidogyne graminicola

Epigenetic processes play a crucial role in the regulation of plant stress responses, but their role in plant–pathogen interactions remains poorly understood. Although histone-modifying enzymes have been observed to be deregulated in galls induced by root-knot nematodes (RKN, Meloidogyne graminicola) in rice, their influence on plant defence and their genome-wide impact has not been comprehensively investigated. First, the role of histone modifications in plant–nematode interactions was confirmed by pharmacological inhibition of histone-modifying enzymes, which all significantly affected rice susceptibility to RKN. For a more specific view, three histone marks, H3K9ac, H3K9me2, and H3K27me3, were subsequently studied by chromatin-immunoprecipitation-sequencing on RKN-induced galls at 3 days postinoculation. While levels of H3K9ac and H3K27me3 were strongly enriched, H3K9me2 was generally depleted in galls versus control root tips. Differential histone peaks were generally associated with plant defence-related genes. Transcriptome analysis using RNA-Seq and RT-qPCR-based validation revealed that genes marked with H3K9ac or H3K9me2 showed the expected activation or repression gene expression pattern, but this was not the case for H3K27me3 marks. Our results indicate that histone modifications respond dynamically to RKN infection, and that posttranslational modifications mainly at H3K9 specifically target plant defence-related genes.