Different roles of MMR proteins during the immune response in Arabidopsis thaliana

RAMOS, ROCÍO S.; SPAMPINATO, CLAUDIA P.

Congreso; Reunión conjunta SAIB SAMIGE; 2020

In nature, plants are exposed to a variety of both biotic and abiotic factors. These factors, both endogenous and environmental, can cause tens of thousands of DNA damage per cell per day. Therefore, to maintain the integrity of the genome, plants have multiple mechanisms for detecting and repairing DNA damage. One of them is the DNA mismatch repair (MMR) system. MMR proteins have been implicated in sensing and correcting DNA-replication-associated errors and in regulating cell cycle progression. In addition, MMR proteins are also involved in the recognition of nucleotide lesions induced by different stresses. Even though both DNA damage and immune responses have been studied in depth separately, whether and how they are connected are largely unknown. The aim of this work was to study the role of MMR proteins during the immune response in Arabidopsis thaliana plants. We investigated the response of MMR deficient plants to the bacterial pathogen Pseudomonas syringae pv. tomato strain DC3000 (Pst DC3000) infection. Colony-forming units (CFU) were quantified in leaves from inoculated plants at 0 and 3 days after inoculation (dpi). We found that plants lacking MutS homolog 7 (MSH7) or MutL homolog 1 (MLH1) were more susceptible to the pathogen than wild type (WT) plants. Interestingly, MSH7 and MLH1 transcript levels were increased in WT plants at 3 dpi. These results are contrasting with those observed in plants lacking the MutS homolog 6 (MSH6), which were more resistant to Pst DC3000 infection, evidenced by a lower CFU and a lower plant growth-inhibition compared with inoculated WT plants. Additionally, msh6/msh7 double mutants showed to be as resistant as msh6 single mutants. In summary, our results suggest that the MMR system could have a role in the immune response in A. thaliana with the effect being dependent on the protein. Given that msh6 mutant plants show an increased rate of somatic homeologous recombination, and that we observed an increased homeologous recombination frequency in response to Pst DC3000 infection, we hypothesize that MSH6 could play a role in the repair of pathogen-induced double strand breaks. Future experiments will allow us testing this hypothesis.