title: Involvement of HLS1 in sugar and auxin signaling in Arabidopsis leaves.
abstract: Sugar regulates a variety of genes and controls plant growth and development similarly to phytohormones. As part of a screen for Arabidopsis mutants with defects in sugar-responsive gene expression, we identified a loss-of-function mutation in the HOOKLESS1 (HLS1) gene. HLS1 was originally identified to regulate apical hook formation of dark-grown seedlings (Lehman et al., 1996, Cell 85: 183-194). In hls1, sugar-induced gene expression in excised leaf petioles was more sensitive to exogenous sucrose than that in the wild type. Exogenous IAA partially repressed sugar-induced gene expression and concomitantly activated some auxin response genes such as AUR3 encoding GH3-like protein. The repression and the induction of gene expression by auxin were attenuated and enhanced, respectively, by the hls1 mutation. These results suggest that HLS1 plays a negative role in sugar and auxin signaling. Because AUR3 GH3-like protein conjugates free IAA to amino acids (Staswick et al., 2002, Plant Cell 14: 1405-1415; Staswick et al., 2005, Plant Cell 17: 616-627), enhanced expression of GH3-like genes would result in a decrease in the free IAA level. Indeed, hls1 leaves accumulated a reduced level of free IAA, suggesting that HLS1 may be involved in negative feedback regulation of IAA homeostasis through the control of GH3-like genes. We discuss the possible mechanisms by which HLS1 is involved in auxin signaling for sugar- and auxin-responsive gene expression and in IAA homeostasis.
authors.affiliation: Division of Developmental Biology, National Institute for Basic Biology, Myodaiji-cho, Okazaki, 444-8585 Japan. maohto@ucdavis.edu
authors.forename: Masa-Aki
authors.initials: MA
authors.lastname: Ohto
authors.forename: Shingo
authors.initials: S
authors.lastname: Hayashi
authors.forename: Shinichiro
authors.initials: S
authors.lastname: Sawa
authors.forename: Akiko
authors.initials: A
authors.lastname: Hashimoto-Ohta
authors.forename: Kenzo
authors.initials: K
authors.lastname: Nakamura
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000502:physiology*; D002241:Carbohydrates / Q000502:physiology*; D018744:DNA, Plant / Q000235:genetics; D025461:Feedback, Physiological / Q000502:physiology; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D017343:Genes, Plant / Q000235:genetics / Q000502:physiology; D006706:Homeostasis; D007210:Indoleacetic Acids / Q000378:metabolism* / Q000494:pharmacology; D009154:Mutation; D010937:Plant Growth Regulators / Q000494:pharmacology; D018515:Plant Leaves / Q000502:physiology*; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology*
chemical_list: D029681:Arabidopsis Proteins; D002241:Carbohydrates; D018744:DNA, Plant; D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; C030737:indoleacetic acid