Functional Analysis of RGA, a Negative Regulator of Gibberellin Signaling in Arabidopsis

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Bioactive gibberellins (GAs) are a class of plant growth hormones, which control diverse processes including seed germination, stem elongation, flower and fruit development. Although the physiological effects of GAs on plant growth are well documented, much less is known about how this hormone signal leads to biochemical and morphological changes. Recent studies using biochemical and genetic approaches have identified three negative regulators (RGA, GAI and SPY) in GA signal transduction pathway in higher plant. The genes encoding these proteins are highly conserved in different species. Both RGA and GAI are likely to function as transcription regulators, whereas SPY is probably an enzyme that modifies other proteins by attaching sugar residues. The current working hypothesis is that SPY may modify and activate RGA and GAI to repress GA signal transduction in the absence of (or in low) GA signal. The basal state of GA signaling is therefore to be repressive, and the GA signal de-represses the pathway by inhibiting the negative regulators. This proposal focuses on elucidating the biochemical function of RGA in regulating GA signal transduction in the model plant Arabidopsis. The specific aims are to examine whether the activity of RGA is modulated by protein modification and/or by alteration of its subcellular localization, and to identify cellular protein(s) that interact with RGA. These studies will shed lights on the molecular mechanisms by which GA controls plant growth and development. This knowledge will also facilitate more effective strategies to improve agricultural crops in the future.