title: Arabidopsis Aux/IAA genes are involved in brassinosteroid-mediated growth responses in a manner dependent on organ type.
abstract: We examined whether auxin/indole-3-acetic acid (Aux/IAA) proteins, which are key players in auxin-signal transduction, are involved in brassinosteroid (BR) responses. iaa7/axr2-1 and iaa17/axr3-3 mutants showed aberrant BR sensitivity and aberrant BR-induced gene expression in an organ-dependent manner. Two auxin inhibitors were tested in terms of BR responses. Yokonolide B inhibited BR responses, whereas p-chlorophenoxyisobutyric acid did not inhibit BR responses. DNA microarray analysis revealed that 108 genes were up-regulated, while only eight genes were down-regulated in iaa7. Among the genes that were up- or down-regulated in axr2, 22% were brassinolide-inducible genes, 20% were auxin-inducible genes, and the majority were sensitive neither to BR nor to auxin. An inhibitor of BR biosynthesis, brassinazole, inhibited auxin induction of the DR5-GUS gene, which consists of a synthetic auxin-response element, a minimum promoter, and a beta-glucuronidase. These results suggest that Aux/IAA proteins function in auxin- and BR-signaling pathways, and that IAA proteins function as the signaling components modulating BR sensitivity in a manner dependent on organ type.
authors.affiliation: RIKEN Plant Science Center, Tsurumi, Yokohama, Kanagawa 230-0045, Japan.
authors.forename: Ayako
authors.initials: A
authors.lastname: Nakamura
authors.forename: Naoko
authors.initials: N
authors.lastname: Nakajima
authors.forename: Hideki
authors.initials: H
authors.lastname: Goda
authors.forename: Yukihisa
authors.initials: Y
authors.lastname: Shimada
authors.forename: Ken-Ichiro
authors.initials: K
authors.lastname: Hayashi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nozaki
authors.forename: Tadao
authors.initials: T
authors.lastname: Asami
authors.forename: Shigeo
authors.initials: S
authors.lastname: Yoshida
authors.forename: Shozo
authors.initials: S
authors.lastname: Fujioka
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development*; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D007210:Indoleacetic Acids / Q000378:metabolism*; D009154:Mutation; D020411:Oligonucleotide Array Sequence Analysis; D013256:Steroids / Q000502:physiology*
chemical_list: D007210:Indoleacetic Acids; D013256:Steroids; C030737:indoleacetic acid