Chloroplastic RecA protein from Physcomitrium patens is able to repair chloroplastic DNA damage by homologous recombination but unable to repair nuclear DNA damage

Plants are unavoidably exposed to a range of environmental stress factors throughout their life. In addition to the external environmental factors, the production of reactive oxygen species as a product of the cellular metabolic process often causes DNA damage and thus affects genome stability. Homologous recombination (HR) is an essential mechanism used for DNA damage repair that helps to maintain genome integrity. Here we report that the recombinase, PpRecA2, a bacterial RecA homolog from moss Physcomitrium patens can partially complement the function of Escherichia coli RecA in the bacterial system. Transcript analysis showed induced expression of PpRecA2 upon experiencing DNA damaging stressors indicating its involvement in DNA damage sensing and repair mechanism. Over-expressing the chloroplast localizing PpRecA2 confers protection to the chloroplast genome against DNA damage by enhancing the chloroplastic HR frequency in transgenic tobacco plants. Although it fails to protect against nuclear DNA damage when engineered for nuclear localization due to the non-availability of interacting partners. Our results indicate that the chloroplastic HR repair mechanism differs from the nucleus, where chloroplastic HR involves RecA as a key player that resembles the bacterial system.