Genetic Interactions between Phytochrome A, Phytochrome B, and Cryptochrome 1 during Arabidopsis Development1

TLDR

In long days, phyA promotes flowering while phyB inhibits it, each suppressing the other's effect. The study assessed de‑etiolation in Arabidopsis mutants lacking phyA, phyB, and cry1 by measuring cotyledon development, hypocotyl growth, and pigment accumulation in 5‑day seedlings under red, far‑red, blue, white light and darkness. PhyA dominates far‑red responses, phyB dominates red‑light responses, and cry1 modulates pigment accumulation; all three photoreceptors act redundantly or additively in blue light, with phyB’s effect on cotyledon expansion requiring cry1, and phytochrome activity is also evident in blue light in a phyAphyB mutant background.

Abstract

Abstract 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. 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. phyA was the major photoreceptor/effector for most far-red-light responses, although phyB and cry1 modulated anthocyanin accumulation in a phyA-dependent manner. phyB was the major photoreceptor in red light, although cry1 acted as a phyA/phyB-dependent modulator of chlorophyll accumulation under these conditions. 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. As reported previously, flowering time in long days was promoted by phyA and inhibited by phyB, with each suppressing the other's effect. 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.