RECA plays a dual role in the maintenance of chloroplast genome stability in Physcomitrella patens

Summary Chloroplast DNA (cp DNA ) encodes essential genes for chloroplast functions, including photosynthesis. Homologous recombination occurs frequently in cp DNA ; however, its significance and underlying mechanism remain poorly understood. In this study, we analyzed the role of a nuclear‐encoded chloroplast‐localized homolog of RecA recombinase, which is a key factor in homologous recombination in bacteria, in the moss Physcomitrella patens . Complete knockout ( KO ) of the P. patens chloroplast RecA homolog RECA 2 caused a modest growth defect and conferred sensitivity to methyl methanesulfonate and UV . The KO mutant exhibited low recovery of cp DNA from methyl methanesulfonate damage, suggesting that RECA 2 knockout impairs repair of damaged cp DNA . The RECA 2 KO mutant also exhibited reduced cp DNA copy number and an elevated level of cp DNA molecule resulting from aberrant recombination between short dispersed repeats (13–63 bp), indicating that the RECA 2 KO chloroplast genome was destabilized. Taken together, these data suggest a dual role for RECA 2 in the maintenance of chloroplast genome stability: RECA 2 suppresses aberrant recombination between short dispersed repeats and promotes repair of damaged DNA .