LIGHT SIGNALING IN ARABIDOPSIS

Of the numerous environmental factors that regulate the growth and dev elopment of plants, light is one of the most important. Plants employ a series of discrete photoreceptors, absorbing in different regions of the light spectrum, in order to monitor the presence, direction, inte nsity, quality and duration of light. The principal signal-transducing photoreceptor families are the red/far-red light-absorbing phytochrom es and the blue/UV-A light-absorbing photoreceptors, which include the cryptochromes. The application of genetic techniques, particularly us ing Arabidopsis, is leading to elucidation of the roles of, and intera ctions between, the various photoreceptors. Genetic screens have also been used to dissect the signal transduction pathways that are trigger ed by photoreceptor activation. The selection of mutants which, when g rown in the dark, resemble light-grown seedlings, has led to the ident ification of a series of nuclear-localised negative regulators: the pr oducts of the COP/DET/FUS genes. These repressors appear to act downst ream of multiple photoreceptors, as well as being involved in other si gnalling pathways. Other COP and DET genes are involved in regulating cellular levels of cytokinins and brassinosteroids, and these regulato rs have also been implicated in light signalling. In addition, several mutants that define positive regulators, which appear to act in pathw ays specific to individual photoreceptors, have also been identified. (C) Elsevier, Paris.