Figure 1.

A co-activator model for GA signaling. Under GA deficient conditions, DELLAs are stable and localized in nuclei. DELLAs interact with GAF1, and exhibiting high transcriptional activity with GAF1. In the presence of GA, DELLAs are degraded via the 26S proteasome pathway. The GAF1-TPR complex exhibits transcriptional repression activity. GA-induced functional conversion of GAF1 complex in plants depends on the degradation of coactivator DELLAs. The ga1–3 or gai-1 mutant accumulate DELLA proteins at a higher level. ΔPAM cannot bind DELLA but can interact with TPR. ΔPAM protein acts as a constitutive repressor with TPR and promotes GA signaling.