SIGNAL-TRANSDUCTION IN THE PHOTOCONTROL OF CHALCONE SYNTHASE GENE-EXPRESSION

The photocontrol of chalcone synthase gene expression was studied by m eans of promoter analyses, in vitro systems, photoreceptor mutants and microinjections, and pharmacological approaches, A 52 bp element of t he promoter is necessary and sufficient to transfer light regulation, Chalcone synthase expression is primarily under the control of phyA an d blue/UV photoreceptors; the latter are functional even in the absenc e of phyA and phyB, Phytochromes seem to be soluble proteins and, with in seconds of irradiation, light-dependent phosphorylations were obser ved in membrane-depleted cytosol preparations, indicating very early p rocesses of signal transduction, Microinjection and pharmacological ex periments reveal that, in the phyA pathway, heterotrimeric G-proteins, cGMP and a genistein-sensitive protein kinase are involved, whereas t he UV pathway includes several trimeric G-proteins and Ca/calmodulin-d ependent steps.