Structural analyses of gibberellin-mediated DELLA protein degradation

Gibberellin promotes plant growth by downregulating growth-repressor DELLA proteins. The gibberellin receptor GID1 binds to DELLA proteins in the presence of gibberellin, triggering their degradation through polyubiquitination by SCFSLY1/GID2 ubiquitin E3 ligase. Despite extensive studies, the molecular mechanisms by which DELLA proteins assemble with SCFSLY1/GID2 to regulate plant growth remain poorly understood. Here, we present two cryo-electron microscopy structures of the Arabidopsis thaliana DELLA protein RGA in complex with GID1A and GID1A-SLY1-ASK2, respectively. Structural analysis revealed that RGA interacts with GID1A and SLY1 through non-overlapping binding surfaces, stabilizing the proteins. This suggests that the SCFSLY1-RGA-GID1A complex assembles through stepwise stabilization induced by gibberellin. Furthermore, the structures indicate that RGA does not interact with IDD family transcription factors when bound to SLY1, suggesting that the binding of DELLA proteins to GID1/SLY1 and transcription factors is mutually exclusive. These findings provide insights into how DELLA proteins regulate transcription factor activity in response to gibberellin.