AtMMS21 regulates DNA damage response and homologous recombination repair in Arabidopsis.

DNA damage is a significant problem in living organisms and DNA repair pathways have been evolved in different species to maintain genomic stability. Here we demonstrated the molecular function of AtMMS21, a component of SMC5/6 complex, in plant DNA damage response. Compared with wild type, the AtMMS21 mutant plants show hypersensitivity in the DNA damaging treatments by MMS, cisplatin and gamma radiation. However, mms21-1 is not sensitive to replication blocking agents hydroxyurea and aphidicolin. The expression of a DNA damage response gene PARP2 is upregulated in mms21-1 under normal condition, suggesting that this signaling pathway is constitutively activated in the mutant. Depletion of ATAXIA-TELANGIECTASIA MUTATED (ATM) in mms21-1 enhances its root growth defect phenotype, indicating that ATM and AtMMS21 may play additive roles in DNA damage pathway. The analysis of homologous recombination frequency showed that the number of recombination events is reduced in mms21-1 mutant. Conclusively, we provided evidence that AtMMS21 plays an important role in homologous recombination for DNA damage repair.