Exoribonuclease RNase R protects Antarctic Pseudomonas syringae Lz4W from DNA damage and oxidative stress

RNase R is a highly processive, 3 -5 exoribonuclease involved in RNA degradation, maturation, and processing in bacteria. In Pseudomonas syringae Lz4W, RNase R interacts with RNase E to form the RNA degradosome complex and is essential for growth at low temperature. RNase R is also implicated in general stress response in many bacteria. We show here that the deletion mutant of rnr gene (encoding RNase R) of P. syringae is highly sensitive to various DNA damaging agents and oxidative stress. RNase R is a multidomain protein comprised of CSD, RNB and S1 domains. We investigated the role of each domain of RNase R and its exoribonuclease activity in nucleic acid damage and oxidative stress response. Our results revealed that the RNB domain alone without its exoribonuclease activity is sufficient to protect against DNA damage and oxidative stress. We also show that the association of RNase R with the degradosome complex is not required for this function. Our study has discovered for the first time a hitherto unknown role of RNase R in protecting P. syringae Lz4W against DNA damage and oxidative stress. ImportanceBacterial exoribonucleases play a crucial role in RNA maturation, degradation, quality control and turnover. In this study, we have uncovered a previously unknown role of 3-5 exoribonuclease RNase R of P. syringae Lz4W in DNA damage and oxidative stress response. Here, we show that neither the exoribonuclease function of RNase R, nor its association with the RNA degradosome complex is essential for this function. Interestingly, in P. syringae Lz4W, hydrolytic RNase R exhibits physiological roles similar to phosphorolytic 3-5 exoribonuclease PNPase of E. coli. Our data suggest that during the course of evolution, mesophilic E. coli and psychrotrophic P. syringae have apparently swapped these exoribonucleases to adapt to their respective environmental growth conditions.