Abstract
In Arabidopsis, two phototropins, phot1 and phot2, function as photoreceptors for hypocotyl phototropism, chloroplast movement, and stomatal opening. Rice (Oryza sativa) has two PHOT1 gene homologs (OsPHOT1a and OsPHOT1b) and one PHOT2 gene homolog. We investigated phototropism of a rice phot1a mutant that has a Tos17 insertion in OsPHOT1a. Seedlings of this mutant showed normal coleoptile and root phototropisms. We therefore produced RNA interference transgenic lines that have substantially reduced OsPHOT1a/OsPHOT1b expressions and also isolated a phot1a/phot1b double mutant from the phot1a mutant mutagenized by γ ray. These transgenic and mutant lines showed no detectable seedling phototropisms to continuous blue light stimulation (0.01-100 μmol m-2 s-1). The phot1b single mutant isolated from the phot1a/phot1b double mutant showed near wild-type levels of phototropisms. These results demonstrated that phot1a and phot1b redundantly mediate phototropisms of coleoptiles and primary roots and are nearly the sole photoreceptors of these phototropisms. It was further found that phot1 functions as a major photoreceptor for the photonastic movement observed in the second leaf.
