Journal Article

Involvement of <i>HLS1</i> in Sugar and Auxin Signaling in <i>Arabidopsis</i> Leaves

Masa-aki Ohto, Shingo Hayashi, Shinichiro Sawa, Akiko Hashimoto-Ohta and Kenzo Nakamura

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 47, issue 12, pages 1603-1611
Published in print December 2006 | ISSN: 0032-0781
Published online December 2006 | e-ISSN: 1471-9053 | DOI:
Involvement of HLS1 in Sugar and Auxin Signaling in Arabidopsis Leaves

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  • Biochemistry
  • Molecular and Cell Biology
  • Plant Sciences and Forestry


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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.

Keywords: Arabidopsis; Auxin; HOOKLESS1; Sugar signaling

Journal Article.  5300 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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