Arabidopsis RPA2:: A genetic link among transcriptional gene silencing, DNA repair, and DNA replication

Transcriptional gene silencing (TGS) controls the expression of transposable elements and of endogenous genes containing promoter repeats, and it is associated with increased DNA methylation. TGS-deficient mutants impaired in siRNA accumulation and/or chromatin modification (ago4, bru1, cmt3, dcl3, ddm1, drd1, drm2, fas1, fas2, hda6, hog1, met1, mom1, nrpd1a, nrpd1b, nrpd2a, rdr2, suvh2, and suvh4) have been identified, but not all mutations affect the same subset of targets [1-20]. Here, we identify Arabidopsis RPA2, a conserved protein with DNA replication and DNA repair motifs [21], as a novel TGS component that is dispensable for endogenous small RNA accumulation. brut, cmt3, ddm1, fast, fast, hda6, hog1, met1, mom1, and rpa2 mutants are impaired in TGS of dispersed Athila/TSI retrotransposons and of the transgene repeat locus L5, but unlike brut, cmt3, ddm1, fas1, fas1, hda6, hog1, and meth the rpa2 and mom1 mutants do not affect the accumulation of 5S-derived siRNAs. Like BRU1, FAS1, FAS2, and MOM1, RPA2 is dispensable for DNA methylation, and rpa2, bru1, fas1, and fas2, but not mom1, mutants are hypersensitive to the DNA damage agent MMS. These results suggest a coordination of the TGS machinery with DNA replication, repair, or recombination machinery at some loci, and they emphasize the diversification of the TGS pathway.