Two independent light signals cooperate in the activation of the plastid psbD blue light-responsive promoter in Arabidopsis

Abstract

The psbD blue light-responsive promoter (BLRP), whose activation has been considered to require strong blue light, is recognized only by SIG5 among six σ factors of plastid RNA polymerase in Arabidopsis. We found SIG5 transcript accumulation was rapidly induced after a 30-min induction time by blue light (470 nm) with an intensity threshold of 5 μmol m −2 s −1 through cryptochromes. Besides this weak blue light, the psbD BLRP activation required the stronger light such as 50 μmol m −2 s −1 irrespective of blue or red light (660 nm). Thus, the two independent light signalings, the cryptochrome-mediated signaling to induce SIG5 transcription and the stronger light-dependent signaling, cooperate to activate the psbD BLRP.