The plastid sigma factor SIG5 is involved in the diurnal regulation of the chloroplast gene psbD in the moss Physcomitrella patens.

We analyzed the function of a plastid sigma factor, SIG5, by targeted gene disruption in the moss Physcomitrella patens. High-intensity light induced the chloroplast gene psbD in the wild-type strain (WT), whereas this induction was nullified in the PpSig5-disrupted strains (DeltaSig5). Moreover, diurnally regulated changes of psbD transcription showed lowered amplitude in DeltaSig5 than in WT. We concluded that the moss SIG5 mediates multiple layers of signals to intricately regulate psbD transcription.