The Mechanism of Gibberellin-Induced Proteolysis of RGA in Arabidopsis

Duke University, Durham NC

Investigators

Abstract

PROJECT ABSTRACT for IBN-0348814 Bioactive gibberellins (GAs) are important plant growth hormones, which promote seed germination, leaf expansion, stem elongation and flower development in higher plants. The dwarf cultivars of wheat and rice developed during the 'Green Revolution' in the 60s and 70s remarkably increased grain yields. Recent studies revealed that these cultivars are modified in their GA production or GA response, illustrating the important role of GA in regulating plant development and in agriculture. The RGA and GAI proteins are two major repressors of GA signaling in the model plant Arabidopsis. Removing both RGA and GAI functions allows for GA-independent stem and leaf growth and flowering. Previous studies illustrated that GA activates its signaling pathway by causing degradation of RGA and GAI and that SLY1, a positive regulator of GA signaling in Arabidopsis, is likely to play a role in targeting RGA and GAI for degradation in response to the GA signal. This proposal is aimed at elucidating the mechanism of GA-induced proteolysis of RGA. A number of biochemical approaches will be taken to determine whether RGA and SLY1 interact in planta. RGA activity is controlled by proteolysis, and possibly by protein modification (e.g., phosphorylation and/or glycosylation). A proteomic approach will be taken to identify the type(s) and site(s) of modification in this protein. These sites will then be altered individually to examine the role(s) of the modified sites in regulating RGA activity and/or stability. The semidwarf wheat cultivars, an essential component of the Green Revolution, contain mutations in the functional ortholog of RGA/GAI (the Rht loci). Because the orthologs of RGA/GAI are highly conserved in plants, the results from the proposed work will likely to have a broad impact in improving quality of agricultural crops. Additional broader impacts include the training of undergraduates, graduate students and postdoctoral fellows, including minorities. The results of the project will also be incorporated into undergraduate courses at Duke.