Interactive signalling by phytochromes and cryptochromes generates de‐etiolation homeostasis inArabidopsis thaliana

ABSTRACT Single, double, triple and quadruple mutants ofphyA,phyB,cry1andcry2were exposed to different sunlight irradiances and photoperiods to investigate the roll played by phytochrome A, phytochrome B, cryptochrome 1 and cryptochrome 2 during de‐etiolation ofArabidopsis thalianaseedlings under natural radiation. Even the quadruple mutant retained some hypocotyl‐growth inhibition by sunlight. Hypocotyl length was strongly affected by interactions among photoreceptors. DoublephyA phyB,phyA cry1, andcry1 cry2mutants were taller than expected from the additive action of single mutations. Some of these redundant interactions required the presence of phytochromes A and/or B. Interactions among photoreceptors resulted in a 44% reduction of the response to irradiance and a 70% reduction of the response to photoperiod. The complex network of interactions among photoreceptors is proposed to buffer de‐etiolation against changes in irradiance and photoperiod, i.e light fluctuations not related to the positions of the shoot above or below soil level