Abstract
Gibberellins regulate germination, elongation and flowering. DELLA proteins are members of the plant-specific GRAS protein family and act as repressors of the GA signaling pathway. DELLA proteins are rapidly degraded in the presence of GA. The degradation mechanism is beginning to be uncovered by the discovery of GA receptor and F-box protein. To understand the downstream signaling of DELLA proteins, we have identified GAF1 that interacts with GAI. GAF1 is a novel transcriptional factor that binds to DNA with sequence specificity. Arabidopsis plants that overexpress GAF1 are early flowering with larger leaves. In contrast the gaf mutant exhibits a semi-dwarf and late flowering phenotype. Exogenous GA cannot restore these phenotypes of the gaf mutant. BiFC analysis indicated that the interaction of GAF1 and GAI disappeared after GA treatment. Our trans-activation assays in yeast and plant cells suggest that GAI protein regulates the function of GAF1. These data suggest that GA controls transcriptional activity via alteration of GAF1 complex components. Based on this model, we are searching for the target genes of GAF1.
