Circadian-Regulated Transcription of thepsbD Light-Responsive Promoter in Wheat Chloroplasts

Abstract

The level of mRNAs derived from the plastid-encoded psbD light-responsive promoter (LRP) is controlled by a circadian clock(s) in wheat (Triticum aestivum). The circadian oscillations in the psbD LRP mRNA level persisted for at least three cycles in continuous light and for one cycle in continuous dark, with maxima in subjective morning and minima in subjective early night. In vitro transcription in chloroplast extracts revealed that the circadian cycles in the psbD LRP mRNA level were dominantly attributed to the circadian-regulated transcription of the psbD LRP. The effects of various mutations introduced into the promoter region on the psbD LRP activity in vitro suggest the existence of two positive elements located between ؊54 and ؊36, which generally enhance the transcription activity, and an anomalous core promoter structure lacking the functional "؊35" element, which plays a crucial role in the circadian fluctuation and light dependency of psbD LRP transcription activity.

Novel nuclear‐encoded proteins interacting with a plastid sigma factor, Sig1, in Arabidopsis thaliana1

“…In plastid, similar promoter structures have been found for some promoters, e.g. psbA promoter has an functional extended 310 element [3], and psbD light-responsive promoter has upstream enhancer elements instead of the 335 element [15,24,25]. On the analogy with the function of Rsd and AsiA, SibI and T3K9.5 may act as anti-sigma factors and/or gene-speci¢c transcription factors.…”

Blue light-induced transcription of plastid-encoded psbD gene is mediated by a nuclear-encoded transcription initiation factor, AtSig5

“…The psbD BLRP contains the less conserved Ϫ35 element. Extensive in vivo and in vitro mutation analyses revealed that light-dependent transcription from the psbD BLRP depends on the Ϫ10, but not the Ϫ35, element (6,37,38). The present report demonstrates that AtSig5 is a specialized factor that is required for light-dependent activation of the psbD BLRP.…”

“…Distinct from standard 70 -type PEP promoters, psbD BLRP activity basically depends on transcription-enhancing sequences, termed the AAG-box, that are located immediately upstream of the Ϫ35 sequence (9). Several proteins are known to bind to the AAG-box and enhance the psbD transcription; they are named AGF (AAG-box factor) (6,35). Considerable debate has arisen regarding molecular mechanisms mediating light regulation of the psbD BLRP.…”

“…The psbD BLRP is activated specifically by high-fluence blue and UV-A light (3,5). It is also regulated by an endogenous circadian rhythm (6). It is assumed that nuclear-encoded transcription regulators control chloroplast transcription, because no genes encoded by higher plant chloroplasts are presumed to be related to transcriptional regulation.…”

Circadian‐regulated expression of a nuclear‐encoded plastid σ factor gene (sigA) in wheat seedlings

“…We previously showed that in wheat chloroplasts, a light‐responsive psbD promoter ( psbD LRP) which has been known to be selectively activated by light is also controlled by a circadian clock [1]. This promoter is known to be recognized by an Escherichia coli ‐type RNA polymerase (RNAP) which functions in chloroplasts of higher plants.…”