Signal transduction in the photocontrol of chalcone synthase gene expression*

Abstract

ABSTRACTThe photocontrol of chalcone synthase gene expression was studied by means of promoter analyses, in vitro systems, photoreceptor mutants and microinjections, and pharmacological approaches. A 52 bp element of the promoter is necessary and sufficient to transfer light regulation. Chalcone synthase expression is primarily under the control of phyA and blue/UV photo receptors; the latter are functional even in the absence of phyA and phyB. Phytochromes seem to be soluble proteins and, within seconds of irradiation, light‐dependent phosphorrylations were observed in membrane‐depleted cytosol preparations, indicating very early processes of signal transduction. Microinjection and pharmacological experiments reveal that, in the phyA pathway, heterotrimeric G‐proteins, cGMP and a genistein‐sensitive protein kinase are involved, whereas the UV pathway includes several trimeric G‐proteins and Ca/calmodulin‐dependent steps.