Abstract
phototropin 1 (phot1) and phot2, which are blue-light receptor kinases, function in blue-light-induced hypocotyl phototropism, chloroplast relocation, and stomatal opening in Arabidopsis thaliana. Previous studies have shown that the proteins RPT2 and NPH3 transduce signals downstream of phototropins to induce the phototropic response. However, the involvement of RPT2 and NPH3 in stomatal opening and in chloroplast relocation mediated by phot1 and phot2 was unknown. Genetic analysis indicates that RPT2 is involved in the phot1-induced phototropic response and stomatal opening, but not in chloroplast relocation or phot2-induced movements. Biochemical analyses indicate that RPT2 is purified in the crude microsomal fraction as well as phot1 and NPH3, and that RPT2 makes a complex with phot1 in vivo. On the other hand, NPH3 is not necessary for stomatal opening or chloroplast relocation. Thus, these results suggest that phot1 and phot2 choose different signal transducers to induce three responses.
