Distinct roles of Deinococcus radiodurans RecFOR and RecA in DNA transformation

RecFOR and RecA are key recombination factors in Deinococcus radiodurans, a bacterium that possesses robust DNA repair capability and is also naturally transformable. While RecFOR functioning as a RecA loader during DNA repair has been established, their relative roles in transformation need further exploration. Here, we constructed recFOR and recA deletion mutants of D. radiodurans, and investigated the effect of these mutations on DNA transformation. recA deletion causes defects in both plasmid and chromosomal transformation. However, it was found that recFOR is not involved in chromosomal transformation, and that only recO and recR mutations compromise plasmid transformation. How recO, recR and recA mutations influence plasmid transformation was further examined by complementation plasmids. Interestingly, the transformation process remains defective in the recA mutant, but gets restored in the recO and recR mutants. This indicates that unlike RecA, RecOR may not be essential for DNA uptake. Therefore, we provide evidence that RecFOR is dispensable for RecA to protect incoming exogenous DNA and to catalyze recombination during transformation. Instead, RecO and RecR are likely to promote later steps in plasmid transformation.