Two domain-disrupted hda6 alleles have opposite epigenetic effects on transgenes and some endogenous targets

HDA6 is a RPD3-like histone deacetylase. In Arabidopsis, it mediates transgene and some endogenous target transcriptional gene silencing (TGS) via histone deacetylation and DNA methylation. Here, we characterized two hda6 mutant alleles that were recovered as second-site suppressors of the DNA demethylation mutant ros1-1. Although both alleles derepressed 35S::NPTII and RD29A::LUC in the ros1-1 background, they had distinct effects on the expression of these two transgenes. In accordance to expression profiles of two transgenes, the alleles have distinct opposite methylation profiles on two reporter gene promoters. Furthermore, both alleles could interact in vitro and in vivo with the DNA methyltransferase1 with differential interactive strength and patterns. Although these alleles accumulated different levels of repressive/active histone marks, DNA methylation but not histone modifications in the two transgene promoters was found to correlate with the level of derepression of the reporter genes between the two had6 alleles. Our study reveals that mutations in different domains of HDA6 convey different epigenetic status that in turn controls the expression of the transgenes as well as some endogenous loci.