Abstract
In A.thaliana there occur six σ factors, sig1-6, nucleus-encoded, each of which is the promoter recognizing subunit of chloroplast bacteria-type RNA polymerase. We have shown that blue-light, not red-light, induces the transcription of sig5 specifically, which leads to blue-light induced psbD transcription. Here we examine which blue-light photoreceptor known so far is involved in the blue-light induction of sig5 transcription, using the two double-mutants in phototropins 1-2 (phot1phot2) or cryptochroms 1-2 (cry1cry2).
A.thaliana wild-type and these mutants were grown under continuous light, and then shifted to the dark for 24 hours. RT-PCR analysis showed no sig5 transcript accumulated in any strains after dark adaptation. Under subsequent blue light irradiation at 5 μmolm-2s-1 for 90 min, sig5 transcript accumulated to wild-type level in phot1phot2 mutant, while it appeared dramatically less in cry1cry2 mutant, suggesting that at least one of cryptochroms 1-2 is involved in the blue-light induction of sig5 transcription.
