Genome stability of Arabidopsis atm, ku80 and rad51b mutants: somatic and transgenerational responses to stress.

DNA double-strand breaks (DSBs) can be repaired via two main mechanisms: non-homologous end joining (NHEJ) and homologous recombination (HR). Our previous work showed that exposure to abiotic stresses resulted in an increase in point mutation frequency (PMF) and homologous recombination frequency (HRF), and these changes were heritable. We hypothesized that mutants impaired in DSB recognition and repair would also be deficient in somatic and transgenerational changes in PMF and HRF. To test this hypothesis, we analyzed the genome stability of the Arabidopsis thaliana mutants deficient in ATM (communication between DNA strand break recognition and the repair machinery), KU80 (deficient in NHEJ) and RAD51B (deficient in HR repair) genes. We found that all three mutants exhibited higher levels of DSBs. Plants impaired in ATM had a lower spontaneous PMF and HRF, whereas ku80 plants had higher frequencies. Plants impaired in RAD51B had a lower HRF. HRF in wild-type, atm and rad51b plants increased in response to several abiotic stressors, whereas it did not increase in ku80 plants. The progeny of stressed wild-type and ku80 plants exhibited an increase in HRF in response to all stresses, and the increase was higher in ku80 plants. The progeny of atm plants showed an increase in HRF only when the parental generation was exposed to cold or flood, whereas the progeny of rad51b plants completely lacked a transgenerational increase in HRF. Our experiments showed that mutants impaired in the recognition and repair of DSBs exhibited changes in the efficiency of DNA repair as reflected by changes in strand breaks, point mutation and HRF. They also showed that the HR RAD51B protein and the protein ATM that recognized damaged DNA might play an important role in transgenerational changes in HRF.