HDAC9 and bacterial infectious disease: The level of H3K4me1 increased in ldl1 ldl2 on all amplicons of PR1 and FRK1. Interestingly, the expression of PR1 and FRK1 before bacterial infection (0 hpi) in the ldl single and double mutants was not significantly different from that of WT plants, likely because LDL1 and LDL2 act synergistically with histone deacetylase complex (HDAC) to repress gene expression (Hung et al., 2018, 2019, 2020).