DIFFERENT ROLES FOR CALCIUM AND CALMODULIN IN PHYTOCHROME-REGULATED AND UV-REGULATED EXPRESSION OF CHALCONE SYNTHASE

Based on knowledge of white light-mediated gene induction events in a photomixotrophic soybean cell culture, a comparative pharmacological d issection of gene expression in response to irradiation with red and U V light was performed in order to examine the molecular basis of cross -talk between phytochrome-and UV-regulated signalling pathways. This h as proved particularly interesting for the gene encoding chalcone synt hase (CHS). Whereas phytochrome control of CHS gene expression is regu lated positively by cGMP and negatively by calcium and calmodulin, in UV light calcium and calmodulin appear to act as positive regulators. Results from combined red and UV irradiations indicate that the phytoc hrome response is activated first and that the UV photoreceptor respon se is activated subsequently. The apparently antagonistic functions of calcium and calmodulin may therefore be able to operate in the same c ell because each response is temporally separated from the other.