The PhyR homolog RSP_1274 of Rhodobacter sphaeroides is involved in defense of membrane stress and has a moderate effect on RpoE (RSP_1092) activity.

These results support the view that the effect of the PhyR-NepR-σ(EcfG) cascade on diverse stress responses varies among members of the Alphaproteobacteria. In the facultative phototroph Rhodobacter sphaeroides PhyR plays no major role in the general stress or the oxidative stress response but rather has a more specialized role in defense of membrane stress.