Involvement of HLS1 in sugar and auxin signaling in Arabidopsis leaves

• Published in: Plant and cell physiology 2006-12, Vol.47 (12), p.1603-1611
• Main Authors: Ohto, M.(National Inst. for Basic Biology, Okazaki, Aichi (Japan)), Hayashi, S, Sawa, S, Hashimoto Ohta, A, Nakamura, K
• Format: Article
• Language: English
• Subjects: Arabidopsis; Arabidopsis - genetics; Arabidopsis - physiology; Arabidopsis Proteins - genetics; Arabidopsis Proteins - physiology; ARABIDOPSIS THALIANA; AUXINAS; AUXINE; AUXINS; AZUCAR; Carbohydrates - physiology; DNA, Plant - genetics; ETAPAS DE DESARROLLO DE LA PLANTA; EXPRESION GENICA; EXPRESSION DES GENES; Feedback, Physiological - physiology; GENE EXPRESSION; Gene Expression Regulation, Plant - drug effects; Genes, Plant - genetics; Genes, Plant - physiology; HOMEOSTASIE; HOMEOSTASIS; Indoleacetic Acids - metabolism; Indoleacetic Acids - pharmacology; Mutation; PLANT DEVELOPMENTAL STAGES; Plant Growth Regulators - pharmacology; Plant Leaves - physiology; Signal Transduction - genetics; Signal Transduction - physiology; STADE DE DEVELOPPEMENT VEGETAL; SUCRE; SUGAR
• ISSN: 0032-0781; 1471-9053
• DOI: 10.1093/pcp/pcl027

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: 616-27), 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.