Plant Hormone Receptors Share Destructive Strategy

Abstract

Gibberellins (GAs) are hydrophobic carboxylic acid molecules that function to regulate plant development. Ueguchi-Tanaka et al. announce the accomplishment of what has been an elusive goal--the identification and characterization of a GA receptor. The authors began with a screen for plants insensitive to the effects of the hormone. One such mutant, gid1 (for gibberellin-insensitive dwarf1) was resistant to GA and appeared to act upstream of known GA signaling intermediates in genetic experiments. Several lines of evidence strongly supported a receptor function for GID1. GID1 bound GA in vitro with micromolar binding affinity, and mutants with reduced biological function had impaired GA binding. GID1 bound to the protein SLR1 in yeast two-hybrid assays in a GA-dependent manner. SLR is a component of GA signaling, a putative transcriptional suppressor whose activity appears to be controlled through ubiquitin-dependent degradation. Finally, transgenic plants overexpressing GID1 showed increased sensitivity to GA. Although the precise signaling mechanism for the GID1 protein, which has sequence similarity to mammalian hormone-sensitive lipases, is not yet clear, it is intriguing that the receptor seems to modulate proteolytic degradation of a negative regulator (SLR1). This mechanism is reminiscent of the mechanism by which auxin, another plant hormone, was recently shown to prompt degradation of a different transcriptional suppressor. Although the auxin receptor and GID1 are structurally distinct, both seem to be modulating targeted destruction of transcriptional regulators by the proteasome. M. Ueguchi-Tanaka, M. Ashikari, M. Nakajima, H. Itoh, E. Katoh, M. Kobayashi, T. Chow, Y. C. Hsing, H. Kitano, I. Yamaguchi, M. Matsuoka, GIBBERELLIN INSENSITIVE DWARF1 encodes a soluble receptor for gibberellin. Nature 437 , 693-698 (2005). [PubMed]