Environmental and endogenous signals can repress the
target genes through reduction in histone acetylation
levels. The REDUCED POTASSIUM DEPENDENCY3
(RPD3) family histone deacetylases (HDACs),
namely HDA6 and HDA19, mediate histone deacetylation
in response to biotic and abiotic stresses in Arabidopsis.
HDA6 is induced by jasmonic acid (JA) and
ethylene [10]. HDA6 is involved in transcriptional gene
silencing (TGS) [11] and RNA-directed DNA methylation
(RdDM) in Arabidopsis [12]. Wounding, infection by
Alternaria brassicicola, and plant hormones (JA and ethylene)
induced the expression of the HDA19/HD1/
AtRPD3A gene. Overexpression of HDA19 in transgenic
plants reduced histone acetylation levels and increased
the expression levels of ETHYLENE RESPONSE FACTOR-1
(ERF1) and PATHOGENESIS-RELATED (PR)
genes. In contrast, RPD3A-RNAi plants exhibited higher
histone acetylation, which was accompanied by downregulation
of ERF1 and PR genes in Arabidopsis [10].
Enhanced HDA6 and HDA19 expression caused by stress
and hormonal signals thus might affect chromatin modi-
fications at several loci.