The Arabidopsis RAD51 paralogs RAD51B, RAD51D and XRCC2 play partially redundant roles in somatic DNA repair and gene regulation

The eukaryotic RAD51 gene family has seven ancient paralogs conserved between plants and animals. Among these, RAD51, DMC1, RAD51C and XRCC3 are important for homologous recombination and/or DNA repair, whereas single mutants in RAD51B, RAD51D or XRCC2 show normal meiosis, and the lineages they represent diverged from each other evolutionarily later than the other four paralogs, suggesting possible functional redundancy. The function of Arabidopsis RAD51B, RAD51D and XRCC2 genes in mitotic DNA repair and meiosis was analyzed using molecular genetic, cytological and transcriptomic approaches. The relevant double and triple mutants displayed normal vegetative and reproductive growth. However, the triple mutant showed greater sensitivity than single or double mutants to DNA damage by bleomycin. RNA-Seq transcriptome analysis supported the idea that the triple mutant showed DNA damage similar to that caused by bleomycin. On bleomycin treatment, many genes were altered in the wild-type but not in the triple mutant, suggesting that the RAD51 paralogs have roles in the regulation of gene transcription, providing an explanation for the hypersensitive phenotype of the triple mutant to bleomycin. Our results provide strong evidence that Arabidopsis XRCC2, RAD51B and RAD51D have complex functions in somatic DNA repair and gene regulation, arguing for further studies of these ancient genes that have been maintained in both plants and animals during their long evolutionary history.