Functional interaction of cryptochrome 1 and phytochrome D

Arabidopsis thaliana wild-type and single, double and triple mutants lackin g phytochrome A (phyA-201), phytochrome B (phyB-5), phytochrome D (phyD-1), phytochrome E (phyE-1), cryptochrome 1 (hy4-2.23n) and cryptochrome 2 (fha -1) were used to study the photoreceptor signal-transduction network. The i nhibition of hypocotyl elongation was analysed using pulses of red light pr eceded by a pre-irradiation of white light. The interactions of phyA, phyB and cry1 have been studied in a series of previous papers. Here we focus on the signal transduction initiated by phyD. We observed that phyD can partl y substitute for the loss of phyB. Specifically, in the phyB background, re d pulses were only effective if both cry1 and phyD were present. The respon se to red pulses, enabled by the pre-irradiation of white light, was comple tely reversible by far-red light. Loss of reversibility occurred with an ap parent half-life of 2 h, similar to the half-life of 3 h observed for the e ffect mediated by phyB. Furthermore, we could show that the response to an end-of-day far-red pulse in phyB depends on both phyD and cry1. In contrast to phyD, a functional interaction of phyE and cry1 could not be detected i n Arabidopsis seedlings.