Abstract
Phototropin (phot) is a blue light receptor in plant, and is involved in phototropism, stomatal opening and chloroplast relocation. Phot has two LOV domains (LOV1, LOV2) that bind a FMN in the N terminal region and a Ser/Thr kinase domain in the C terminal region. In the dark, the kinase is inhibited by mainly LOV2. Upon blue light activation, a covalent bond is formed between FMN and a conserved Cys residue, and then the inhibition is canceled through structural changes of LOV2. Activated kinase induces autophosphorylation that is necessary for expression of the photoresponses.
We have reported that Arabidopsis phot1/phot2 double mutant rescued with a R/K mutated phot2 (Arg513 in LOV2 is substituted with Lys) showed only a slight chloroplast avoidance response under 100 μmol m-2 s-1 irradiation. In this study, we measured the chloroplast relocation responses of the R/K mutant under higher intensity light. Accumulation and avoidance responses were observed by 200 and 900 μmol m-2 s-1 irradiation, respectively. The results can be interpreted by the large reduction of the photosensitivity in the R/K mutant shifting the fluence-response curve to the higher light intensity.
