title: GNOM regulates root hydrotropism and phototropism independently of PIN-mediated auxin transport.
abstract: Plant roots exhibit tropisms in response to gravity, unilateral light and moisture gradients. During gravitropism, an auxin gradient is established by PIN auxin transporters, leading to asymmetric growth. GNOM, a guanine nucleotide exchange factor of ARF GTPase (ARF-GEF), regulates PIN localization by regulating subcellular trafficking of PINs. Therefore, GNOM is important for gravitropism. We previously isolated mizu-kussei2 (miz2), which lacks hydrotropic responses; MIZ2 is allelic to GNOM. Since PIN proteins are not required for root hydrotropism in Arabidopsis, the role of GNOM in root hydrotropism should differ from that in gravitropism. To examine this possibility, we conducted genetic analysis of gnom(miz2) and gnom trans-heterozygotes. The mutant gnom(miz2), which lacks hydrotropic responses, was partially recovered by gnom(emb30-1), which lacks GEF activity, but not by gnom(B4049), which lacks heterotypic domain interactions. Furthermore, the phototropic response of gnom trans-heterozygotes differed from that of the pin2 mutant allele eir1-1. Moreover, defects in the polarities of PIN2 and auxin distribution in a severe gnom mutant were recovered by gnom(miz2). Therefore, an unknown GNOM-mediated vesicle trafficking system may mediate root hydrotropism and phototropism independently of PIN trafficking.
authors.affiliation: Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
authors.forename: Teppei
authors.initials: T
authors.lastname: Moriwaki
authors.affiliation: Department of Biology, Faculty of Science, Yamagata University, 1-4-12 Kojirakawa-machi, Yamagata 990-8560, Japan. Electronic address: miyazawa@sci.kj.yamagata-u.ac.jp.
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Miyazawa
authors.affiliation: Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
authors.forename: Nobuharu
authors.initials: N
authors.lastname: Fujii
authors.affiliation: Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan. Electronic address: hideyuki@ige.tohoku.ac.jp.
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Takahashi
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000502:physiology; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D001692:Biological Transport; D022162:Cytoplasmic Vesicles; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics* / Q000378:metabolism; D006579:Heterozygote; D007210:Indoleacetic Acids / Q000378:metabolism*; D008027:Light; D009154:Mutation; D018524:Phototropism / Q000235:genetics*; D018517:Plant Roots / Q000502:physiology*; D018523:Tropism / Q000235:genetics*; D014867:Water
chemical_list: D029681:Arabidopsis Proteins; D020662:Guanine Nucleotide Exchange Factors; D007210:Indoleacetic Acids; D014867:Water; C088087:GNOM protein, Arabidopsis; C117013:AT5G57090 protein, Arabidopsis
keywords: Auxin; GNOM; Gravitropism; Hydrotropism; PIN2; Phototropism