title: Functional analyses of the activation loop of phototropin2 in Arabidopsis.
abstract: Phototropins (phot1 and phot2) are autophosphorylating blue-light receptor kinases that mediate blue-light responses such as phototropism, chloroplast accumulation, and stomatal opening in Arabidopsis (Arabidopsis thaliana). Only phot2 induces the chloroplast avoidance response under strong blue light. The serine (Ser) residues of the kinase activation loop in phot1 are autophosphorylated by blue light, and autophosphorylation is essential for the phot1-mediated responses. However, the role of autophosphorylation in phot2 remains to be determined. In this study, we substituted the conserved residues of Ser-761 and Ser-763 with alanine (S761A S763A) in the phot2 activation loop and analyzed their function by investigating the phot2-mediated responses after the transformation of phot1 phot2 double mutant with this mutant phot2 gene. Transgenic plants expressing the mutant phot2 protein exhibited impaired responses in chloroplast movement, stomatal opening, phototropic bending, leaf flattening, and plant growth; and those expressing phot2 with S761D S763D mutations showed the normal responses. Substitution of both Ser-761 and Ser-763 with alanine in phot2 did not significantly affect the kinase activity in planta. From these results, we conclude that phosphorylation of Ser-761 and Ser-763 in the activation loop may be a common primary step for phot2-mediated responses.
authors.affiliation: Department of Biology, Faculty of Science, Kyushu University, Hakozaki, Fukuoka 812-8581, Japan.
authors.forename: Shin-ichiro
authors.initials: S
authors.lastname: Inoue
authors.forename: Tomonao
authors.initials: T
authors.lastname: Matsushita
authors.forename: Yuta
authors.initials: Y
authors.lastname: Tomokiyo
authors.forename: Masaki
authors.initials: M
authors.lastname: Matsumoto
authors.forename: Keiichi I
authors.initials: KI
authors.lastname: Nakayama
authors.forename: Toshinori
authors.initials: T
authors.lastname: Kinoshita
authors.forename: Ken-ichiro
authors.initials: K
authors.lastname: Shimazaki
mesh_terms: D000818:Animals; D000906:Antibodies; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000502:physiology / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism; D008027:Light; D058503:Mesophyll Cells; D016297:Mutagenesis, Site-Directed; D050505:Mutant Proteins; D009154:Mutation; D010641:Phenotype; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D018524:Phototropism; D018515:Plant Leaves / Q000201:enzymology / Q000235:genetics / Q000502:physiology / Q000528:radiation effects; D030821:Plants, Genetically Modified; D017346:Protein Serine-Threonine Kinases; D011817:Rabbits; D011993:Recombinant Fusion Proteins; D036226:Seedlings / Q000201:enzymology / Q000235:genetics / Q000502:physiology / Q000528:radiation effects; D012694:Serine
chemical_list: D000906:Antibodies; D029681:Arabidopsis Proteins; D050505:Mutant Proteins; C423903:PHOT2 protein, Arabidopsis; D010750:Phosphoproteins; D011993:Recombinant Fusion Proteins; D012694:Serine; C103646:NPH1 protein, Arabidopsis; D017346:Protein Serine-Threonine Kinases