title: phot1 inhibition of ABCB19 primes lateral auxin fluxes in the shoot apex required for phototropism.
abstract: It is well accepted that lateral redistribution of the phytohormone auxin underlies the bending of plant organs towards light. In monocots, photoreception occurs at the shoot tip above the region of differential growth. Despite more than a century of research, it is still unresolved how light regulates auxin distribution and where this occurs in dicots. Here, we establish a system in Arabidopsis thaliana to study hypocotyl phototropism in the absence of developmental events associated with seedling photomorphogenesis. We show that auxin redistribution to the epidermal sites of action occurs at and above the hypocotyl apex, not at the elongation zone. Within this region, we identify the auxin efflux transporter ATP-BINDING CASSETTE B19 (ABCB19) as a substrate target for the photoreceptor kinase PHOTOTROPIN 1 (phot1). Heterologous expression and physiological analyses indicate that phosphorylation of ABCB19 by phot1 inhibits its efflux activity, thereby increasing auxin levels in and above the hypocotyl apex to halt vertical growth and prime lateral fluxes that are subsequently channeled to the elongation zone by PIN-FORMED 3 (PIN3). Together, these results provide new insights into the roles of ABCB19 and PIN3 in establishing phototropic curvatures and demonstrate that the proximity of light perception and differential phototropic growth is conserved in angiosperms.
authors.affiliation: Institute of Molecular Cell and Systems Biology, University of Glasgow, Glasgow, United Kingdom. john.christie@glasgow.ac.uk
authors.forename: John M
authors.initials: JM
authors.lastname: Christie
authors.forename: Haibing
authors.initials: H
authors.lastname: Yang
authors.forename: Gregory L
authors.initials: GL
authors.lastname: Richter
authors.forename: Stuart
authors.initials: S
authors.lastname: Sullivan
authors.forename: Catriona E
authors.initials: CE
authors.lastname: Thomson
authors.forename: Jinshan
authors.initials: J
authors.lastname: Lin
authors.forename: Boosaree
authors.initials: B
authors.lastname: Titapiwatanakun
authors.forename: Margaret
authors.initials: M
authors.lastname: Ennis
authors.forename: Eirini
authors.initials: E
authors.lastname: Kaiserli
authors.forename: Ok Ran
authors.initials: OR
authors.lastname: Lee
authors.forename: Jiri
authors.initials: J
authors.lastname: Adamec
authors.forename: Wendy A
authors.initials: WA
authors.lastname: Peer
authors.forename: Angus S
authors.initials: AS
authors.lastname: Murphy
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000378:metabolism*; D000064:Acclimatization; D017360:Arabidopsis / Q000254:growth & development / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D001692:Biological Transport; D003624:Darkness; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D018546:Hypocotyl / Q000378:metabolism; D007210:Indoleacetic Acids / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D018524:Phototropism; D018520:Plant Shoots / Q000378:metabolism*; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases; D011993:Recombinant Fusion Proteins / Q000378:metabolism
chemical_list: C532604:ABCB19 protein, Arabidopsis; D018528:ATP-Binding Cassette Transporters; D029681:Arabidopsis Proteins; D007210:Indoleacetic Acids; D010750:Phosphoproteins; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; C103646:NPH1 protein, Arabidopsis; D017346:Protein Serine-Threonine Kinases