title: Tryptophan-dependent auxin biosynthesis is required for HD-ZIP III-mediated xylem patterning.
abstract: The development and growth of higher plants is highly dependent on the conduction of water and minerals throughout the plant by xylem vessels. In Arabidopsis roots the xylem is organized as an axis of cell files with two distinct cell fates: the central metaxylem and the peripheral protoxylem. During vascular development, high and low expression levels of the class III HD-ZIP transcription factors promote metaxylem and protoxylem identities, respectively. Protoxylem specification is determined by both mobile, ground tissue-emanating miRNA165/6 species, which downregulate, and auxin concentrated by polar transport, which promotes HD-ZIP III expression. However, the factors promoting high HD-ZIP III expression for metaxylem identity have remained elusive. We show here that auxin biosynthesis promotes HD-ZIP III expression and metaxylem specification. Several auxin biosynthesis genes are expressed in the outer layers surrounding the vascular tissue in Arabidopsis root and downregulation of HD-ZIP III expression accompanied by specific defects in metaxylem development is seen in auxin biosynthesis mutants, such as trp2-12, wei8 tar2 or a quintuple yucca mutant, and in plants treated with L-kynurenine, a pharmacological inhibitor of auxin biosynthesis. Some of the patterning defects can be suppressed by synthetically elevated HD-ZIP III expression. Taken together, our results indicate that polar auxin transport, which was earlier shown to be required for protoxylem formation, is not sufficient to establish a proper xylem axis but that root-based auxin biosynthesis is additionally required.
authors.affiliation: Institute of Biotechnology, Department of Bio and Environmental Sciences, University of Helsinki, FIN-00014, Finland.
authors.forename: Robertas
authors.initials: R
authors.lastname: Ursache
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Miyashima
authors.forename: Qingguo
authors.initials: Q
authors.lastname: Chen
authors.forename: Anne
authors.initials: A
authors.lastname: Vatén
authors.forename: Keiji
authors.initials: K
authors.lastname: Nakajima
authors.forename: Annelie
authors.initials: A
authors.lastname: Carlsbecker
authors.forename: Yunde
authors.initials: Y
authors.lastname: Zhao
authors.forename: Ykä
authors.initials: Y
authors.lastname: Helariutta
authors.forename: Jan
authors.initials: J
authors.lastname: Dettmer
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D019521:Body Patterning; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D007210:Indoleacetic Acids / Q000378:metabolism*; D009154:Mutation; D010105:Oxygenases / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000254:growth & development / Q000378:metabolism; D030821:Plants, Genetically Modified; D015398:Signal Transduction; D014364:Tryptophan / Q000378:metabolism*; D052584:Xylem / Q000254:growth & development / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; C493946:HD-Zip protein, Arabidopsis; D018398:Homeodomain Proteins; D007210:Indoleacetic Acids; D014364:Tryptophan; D010105:Oxygenases; C422746:YUC protein, Arabidopsis
keywords: Arabidopsis thaliana; Auxin biosynthesis; HD-ZIP III; Metaxylem