Abstract
Gibberellins regulate seed germination, shoot 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 has been 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 DELLA protein by modified yeast two hybrid screening. GAF1 is a novel transcriptional factor. Arabidopsis plants that overexpress GAF1 are early flowering with larger leaves. In contrast the gaf mutant exhibits a semi-dwarf and late flowering phenotype. BiFC analysis indicated that the interaction of GAF1 and DELLA protein disappeared after GA treatment. Moreover we isolated a WD repeat protein as another GAF1 interaction protein. Our trans-activation assays in yeast and plant cells suggest that DELLA and the WD repeat 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.
