The role of ATXR6 expression in modulating genome stability and transposable element repression in .

ARABIDOPSIS TRITHORAX-RELATED PROTEIN 5 (ATXR5) AND ATXR6 are required for the deposition of H3K27me1 and for maintaining genomic stability in Reduction of ATXR5/6 activity results in activation of DNA damage response genes, along with tissue-specific derepression of transposable elements (TEs), chromocenter decompaction, and genomic instability characterized by accumulation of excess DNA from heterochromatin. How loss of ATXR5/6 and H3K27me1 leads to these phenotypes remains unclear. Here we provide extensive characterization of the hypomorphic mutant by comprehensively examining gene expression and epigenetic changes in the mutant. We found that the tissue-specific phenotypes of TE derepression and excessive DNA in this mutant correlated with residual expression from the hypomorphic allele. However, up-regulation of DNA damage genes occurred regardless of levels and thus appears to be a separable process. We also isolated an -null allele which showed that ATXR5 and ATXR6 are required for female germline development. Finally, we characterize three previously reported suppressors of the hypomorphic mutant and show that these rescue via distinct mechanisms, two of which involve increasing H3K27me1 levels.