Abstract
Plant roots can turn green when exposed to light. We have reported that blue light is far more effective at inducing root greening than red light in Arabidopsis, and this blue light response is regulated mainly by cryptochrome 1 (cry1) (Usami et al., 2002 JSPP Annual Meeting).
In the present study, we found that the mutant lacking both phytochrome A (phyA) and phytochrome B (phyB) did not respond to blue light at all. This strongly suggested that either phyA or phyB, in addition to cry1, was required for this blue light response and that phytochromes and cryptochromes synergistically regulated the root greening. The expresssion of photosynthetic genes was regulated in the same way. Dichromatic irradiation experiments indicated that this interaction depends on the level of phyB PFR. Identification of the essential domain of phyB for this synergistic interaction is now in progress.
