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, but the downstream signaling of DELLA proteins is unknown.
We have identified a GAI (an Arabidopsis DELLA protein)-interacting protein, named GAF1, using yeast Tup1-two hybrid screening that we developed. GAF1 is a novel transcriptional factor that binds to DNA in a sequence-specific manner. Arabidopsis plants that overexpress GAF1 are early flowering with larger leaves. Our trans-activation assay in yeast suggests that GAF1 has a weak transcriptional activity on its own, but it acts as a strong transcriptional activator in combination with a DELLA protein. We will present a model of GA signaling downstream of DELLA proteins.
