title: PIN auxin efflux carriers are necessary for pulse-induced but not continuous light-induced phototropism in Arabidopsis.
abstract: Auxin efflux carrier PIN-FORMED (PIN) proteins are thought to have central roles in regulating asymmetrical auxin translocation during tropic responses, including gravitropism and phototropism, in plants. Although PIN3 is known to be involved in phototropism in Arabidopsis (Arabidopsis thaliana), no severe defects of phototropism in any of the pin mutants have been reported. We show here that the pulse-induced, first positive phototropism is impaired partially in pin1, pin3, and pin7 single mutants, and severely in triple mutants. In contrast, such impairment was not observed in continuous-light-induced second positive phototropism. Analysis with an auxin-reporter gene demonstrated that PIN3-mediated auxin gradients participate in pulse-induced phototropism but not in continuous-light-induced phototropism. Similar functional separation was also applicable to PINOID, a regulator of PIN localization. Our results strongly suggest the existence of functionally distinct mechanisms i.e. a PIN-dependent mechanism in which transient stimulation is sufficient to induce phototropism, and a PIN-independent mechanism that requires continuous stimulation and does not operate in the former phototropism process. Although a previous study has proposed that blue-light photoreceptors, the phototropins, control PIN localization through the transcriptional down-regulation of PINOID, we could not detect this blue-light-dependent down-regulation event, suggesting that other as yet unknown mechanisms are involved in phototropin-mediated phototropic responses.
authors: Graduate School of Science and Technology, Niigata University, 8050 Ikarashi 2-no-cho, Nishi-ku, Niigata 950-2181, Japan.
authors: Ken
authors: K
authors: Haga
authors: Tatsuya
authors: T
authors: Sakai
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism; D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development* / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport; D003116:Color; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D017930:Genes, Reporter; D018522:Gravitropism; D018546:Hypocotyl / Q000235:genetics / Q000528:radiation effects; D007210:Indoleacetic Acids / Q000378:metabolism; D008027:Light; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D056949:Phototropins / Q000235:genetics / Q000378:metabolism; D018524:Phototropism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D013997:Time Factors; D014158:Transcription, Genetic
chemical_list: C532604:ABCB19 protein, Arabidopsis; D018528:ATP-Binding Cassette Transporters; D029681:Arabidopsis Proteins; D007210:Indoleacetic Acids; D026901:Membrane Transport Proteins; C116363:PIN1 protein, Arabidopsis; C449300:PIN3 protein, Arabidopsis; C479554:PIN7 protein, Arabidopsis; D056949:Phototropins; C405165:PINOID protein, Arabidopsis; D017346:Protein Serine-Threonine Kinases