title: Phototropins function in high-intensity blue light-induced hypocotyl phototropism in Arabidopsis by altering cytosolic calcium.
abstract: Phototropins (phot1 and phot2), the blue light receptors in plants, regulate hypocotyl phototropism in a fluence-dependent manner. Especially under high fluence rates of blue light (HBL), the redundant function mediated by both phot1 and phot2 drastically restricts the understanding of the roles of phot2. Here, systematic analysis of phototropin-related mutants and overexpression transgenic lines revealed that HBL specifically induced a transient increase in cytosolic Ca(2+) concentration ([Ca(2+)]cyt) in Arabidopsis (Arabidopsis thaliana) hypocotyls and that the increase in [Ca(2+)]cyt was primarily attributed to phot2. Pharmacological and genetic experiments illustrated that HBL-induced Ca(2+) increases were modulated differently by phot1 and phot2. Phot2 mediated the HBL-induced increase in [Ca(2+)]cyt mainly by an inner store-dependent Ca(2+)-release pathway, not by activating plasma membrane Ca(2+) channels. Further analysis showed that the increase in [Ca(2+)]cyt was possibly responsible for HBL-induced hypocotyl phototropism. An inhibitor of auxin efflux carrier exhibited significant inhibitions of both phototropism and increases in [Ca(2+)]cyt, which indicates that polar auxin transport is possibly involved in HBL-induced responses. Moreover, PHYTOCHROME KINASE SUBSTRATE1 (PKS1), the phototropin-related signaling element identified, interacted physically with phototropins, auxin efflux carrier PIN-FORMED1 and calcium-binding protein CALMODULIN4, in vitro and in vivo, respectively, and HBL-induced phototropism was impaired in pks multiple mutants, indicating the role of the PKS family in HBL-induced phototropism. Together, these results provide new insights into the functions of phototropins and highlight a potential integration point through which Ca(2+) signaling-related HBL modulates hypocotyl phototropic responses.
authors.affiliation: Institute of Plant Stress Biology, State Key Laboratory of Cotton Biology, School of Life Sciences, Henan University, Kaifeng 475004, People's Republic of China.
authors.forename: Xiang
authors.initials: X
authors.lastname: Zhao
authors.forename: Yan-Liang
authors.initials: YL
authors.lastname: Wang
authors.forename: Xin-Rong
authors.initials: XR
authors.lastname: Qiao
authors.forename: Jin
authors.initials: J
authors.lastname: Wang
authors.forename: Lin-Dan
authors.initials: LD
authors.lastname: Wang
authors.forename: Chang-Shui
authors.initials: CS
authors.lastname: Xu
authors.forename: Xiao
authors.initials: X
authors.lastname: Zhang
mesh_terms: D017360:Arabidopsis / Q000378:metabolism / Q000502:physiology; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000235:genetics / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D018546:Hypocotyl / Q000502:physiology; D007210:Indoleacetic Acids / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D008027:Light; D008565:Membrane Proteins; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D018524:Phototropism / Q000502:physiology*; D030821:Plants, Genetically Modified; D017346:Protein Serine-Threonine Kinases; D015398:Signal Transduction
chemical_list: D029681:Arabidopsis Proteins; C586315:CAM4 protein, Arabidopsis; D002147:Calmodulin; D007210:Indoleacetic Acids; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; C423903:PHOT2 protein, Arabidopsis; C116363:PIN1 protein, Arabidopsis; C485609:PKS1 protein, Arabidopsis; D010750:Phosphoproteins; C103646:NPH1 protein, Arabidopsis; D017346:Protein Serine-Threonine Kinases; D002118:Calcium