Here, we demonstrate in vitro, using purified recombinant photoreceptors, that Arabidopsis CRY1 and CRY2 (cryptochrome) are substrates for phosphorylation by a phytochrome A–associated kinase activity. In addition to the effector/modulator relationships described above, measurements of hypocotyls from blue-light-grown seedlings demonstrated phytochrome activity in blue light and cry1 activity in a phyAphyB mutant background.Plants have at least two major photosensory receptors: phytochrome (absorbing primarily red/far-red light) and cryptochrome (absorbing blue/UV-A light) considerable physiological and genetic evidence suggests some form of communication or functional dependence between the receptors.
As reported previously, flowering time in long days was promoted by phyA and inhibited by phyB, with each suppressing the other's effect.
All three photoreceptors contributed to most blue light deetiolation responses, either redundantly or additively however, phyB acted as a modulator of cotyledon expansion dependent on the presence of cry1. phyB was the major photoreceptor in red light, although cry1 acted as a phyA/phyB-dependent modulator of chlorophyll accumulation under these conditions.
phyA was the major photoreceptor/effector for most far-red-light responses, although phyB and cry1 modulated anthocyanin accumulation in a phyA-dependent manner. Cotyledon unhooking, unfolding, and expansion, hypocotyl growth, and the accumulation of chlorophylls and anthocyanin in 5-d-old seedlings were measured under each light condition and in the dark. Single, double, and triple null combinations of Arabidopsis mutants lacking the photoreceptors phytochrome (phy) A (phyA-201), phyB (phyB-5), and cryptochrome (cry) 1 (hy4-2.23n) were examined for de-etiolation responses in high-fluence red, far-red, blue, and broad-spectrum white light.
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