Plant and Cell Physiology Advance Access published online on October 27, 2006
Plant and Cell Physiology, doi:10.1093/pcp/pcl027
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1 Division of Developmental Biology, National Institute for Basic Biology, Myodaiji-cho, Okazaki 444-8585, Japan; Present address: Dept of Plant Sciences, Plant Reproductive Biology Building, Mail Stop 5, University of California, One Shields Avenue, Davis, CA 95616
* To whom correspondence should be addressed. Sugar regulates variety of genes and controls plant growth and development similar to phyto-hormones. As a 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). In hls1, sugar-induced gene expression in excised leaf-petioles was more sensitive to exogenous sucrose than that in wild type. Exogenous indole-3-acetic acid (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, 2005), enhanced expression of GH3-like genes would result in a decrease in free IAA level. Indeed, hls1 leaves accumulated 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 on the possible mechanisms in which HLS1 is involved in auxin signaling for sugar- and auxin-responsive gene expression and in IAA-homeostasis.
Regular paper
Involvement of HLS1 in sugar and auxin signaling in Arabidopsis leaves
Masa-aki Ohto 1 *, Shingo Hayashi 2, Shinichiro Sawa 3, Akiko Hashimoto-Ohta 4, and Kenzo Nakamura 5
2 Laboratory of Biochemistry, Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa-ku, Nagoya 464-8601, Japan; Present address: Medical and Biological Laboratories, Ina , Nagano 396-0002, Japan
3 Department of Biological Sciences, Graduate School of Science, University of Tokyo, Hongo, Tokyo 113-0033, Japan
4 Division of Developmental Biology, National Institute for Basic Biology, Myodaiji-cho, Okazaki 444-8585, Japan
5 Division of Developmental Biology, National Institute for Basic Biology, Myodaiji-cho, Okazaki 444-8585, Japan; Laboratory of Biochemistry, Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa-ku, Nagoya 464-8601, Japan
Masa-aki Ohto, E-mail: maohto{at}ucdavis.edu
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