title: Cytokinin is required for escape but not release from auxin mediated apical dominance.
abstract: Auxin produced by an active primary shoot apex is transported down the main stem and inhibits the growth of the axillary buds below it, contributing to apical dominance. Here we use Arabidopsis thaliana cytokinin (CK) biosynthetic and signalling mutants to probe the role of CK in this process. It is well established that bud outgrowth is promoted by CK, and that CK synthesis is inhibited by auxin, leading to the hypothesis that release from apical dominance relies on an increased supply of CK to buds. Our data confirm that decapitation induces the expression of at least one ISOPENTENYLTRANSFERASE (IPT) CK biosynthetic gene in the stem. We further show that transcript abundance of a clade of the CK-responsive type-A Arabidopsis response regulator (ARR) genes increases in buds following CK supply, and that, contrary to their typical action as inhibitors of CK signalling, these genes are required for CK-mediated bud activation. However, analysis of the relevant arr and ipt multiple mutants demonstrates that defects in bud CK response do not affect auxin-mediated bud inhibition, and increased IPT transcript levels are not needed for bud release following decapitation. Instead, our data suggest that CK acts to overcome auxin-mediated bud inhibition, allowing buds to escape apical dominance under favourable conditions, such as high nitrate availability.
authors.affiliation: Department of Biology, University of York, Heslington, York, YO10 5DD, UK.
authors.forename: Dörte
authors.initials: D
authors.lastname: Müller
authors.affiliation: Sainsbury Laboratory, University of Cambridge, Bateman Street, Cambridge, CB2 1LR, UK.
authors.forename: Tanya
authors.initials: T
authors.lastname: Waldie
authors.affiliation: Biology Department, University of North Carolina, Chapel Hill, NC, 27599, USA.
authors.forename: Kaori
authors.initials: K
authors.lastname: Miyawaki
authors.affiliation: Department of Biological Sciences, Graduate School of Science, Osaka University, Machikaneyama, Toyonaka, Osaka, 560-0043, Japan.
authors.forename: Jennifer P C
authors.initials: JP
authors.lastname: To
authors.affiliation: Sainsbury Laboratory, University of Cambridge, Bateman Street, Cambridge, CB2 1LR, UK.
authors.forename: Charles W
authors.initials: CW
authors.lastname: Melnyk
authors.affiliation: Department of Biological Sciences, Graduate School of Science, Osaka University, Machikaneyama, Toyonaka, Osaka, 560-0043, Japan.
authors.forename: Joseph J
authors.initials: JJ
authors.lastname: Kieber
authors.affiliation: Biology Department, University of North Carolina, Chapel Hill, NC, 27599, USA.
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Kakimoto
authors.affiliation: Department of Biology, University of York, Heslington, York, YO10 5DD, UK.|Sainsbury Laboratory, University of Cambridge, Bateman Street, Cambridge, CB2 1LR, UK.
authors.forename: Ottoline
authors.initials: O
authors.lastname: Leyser
mesh_terms: D019883:Alkyl and Aryl Transferases / Q000235:genetics / Q000378:metabolism; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics; D003583:Cytokinins / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D007210:Indoleacetic Acids / Q000378:metabolism*; D005810:Multigene Family; D009154:Mutation; D009566:Nitrates / Q000378:metabolism; D018520:Plant Shoots / Q000254:growth & development / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics
chemical_list: C509519:ARR3 protein, Arabidopsis; D029681:Arabidopsis Proteins; D003583:Cytokinins; D007210:Indoleacetic Acids; D009566:Nitrates; D014157:Transcription Factors; D019883:Alkyl and Aryl Transferases; C024274:adenylate isopentenyltransferase
keywords: Arabidopsis thaliana; Isopentenyltransferase; apical dominance; auxin; cytokinin; shoot branching; type-A Arabidopsis response regulators