Blue light specific and differential expression of a plastid sigma factor, Sig5 in Arabidopsis thaliana.

The transcription of plastid gene psbD is under the control of the BLRP (blue-light-responsive promoter) recognized by plastid-encoded RNA polymerase, in which nuclear-encoded sigma factors play a crucial role in the promoter recognition. We examined the effects of light on mRNA levels of six different SIG genes in Arabidopsis and found that blue light extensively induced the accumulation of SIG5 transcripts, but red light did not. The blue light specificity was not observed in the accumulations of remaining five SIG genes. The blue light dependency of the SIG5 expression well explains the light-dependent behavior of the psbD BLRP.