Phytochrome and COP1 Regulates Abundance of Phytochrome Interacting Factor 3

Abstract

To sense the environmental factor light, plants have evolved different sensory photoreceptors ([Kendrick and Kronenberg 1994]). In Arabidopsis five members of a small gene family (PHYA to PHYE) encode the photoreceptor phytochromes ([Clack et al 1994]). Phytochromes are R/FR photoreversible chromoproteins, which form dimers with a molecular mass of ca. 120kDa per monomer and in which an open-chain tetrapyrrole chromophore is autocatalytically attached to the apoprotein ([Lagarias and Lagarias 1989], [Eichenberg et al 2000]). R induced formation of the FR absorbing active form of phytochrome (Pfr) initiates a signalling cascade which controls plant photomorphogenesis. Of these phytochromes, phyA has a very specific mode of action by controlling very low fluence responses (VLFR) and far-red high irradiance responses (HIR) ([Furuya and Schifer 1996]). VLFR is initiated even by a few seconds of starlight and is saturated at about μmol/m², whereas HIR requires prolonged irradiation with continuous far-red light (cFR). In contrast to phyA, phyB-E mediate responses to continuous red light (cR) and show the R/FR reversible induction responses. Between light absorption by photoreceptors and physiological and developmental responses lies a web of interacting factors and interacting pathways, either directly involved in or otherwise impinging upon light signal transduction.