Abstract
Phototropism allows plants to change their growth direction in response to the light source location, and contributes to photosynthesis in green plants. The phototropic response is initiated by the blue-light photoreceptors, phototropins (phots). Recent molecular genetic studies using mutants of Arabidopsis thaliana and rice have shown that an adapter-like protein, NPH3, is essential for the phototropic response in plants. NPH3 is phosphorylated under dark conditions and dephosphorylated by blue-light irradiation in a phot1-dependent manner. Although the dephosphorylation of the NPH3 proteins appears to play an important role in the phototropic response, its function has been unknown yet. To understand the function of phosphorylation and dephosphorylation of NPH3 during the phototropic response, we have performed an identification of the NPH3 phosphorylation kinase. By an immunoscreening method using an anti-phospho-NPH3-peptide antibody, we have isolated two genes encoding protein kinases to phosphorylate NPH3. Those kinases show the activity to phosphorylates the NPH3 protein in E. coli and in vitro .
