COP1 destabilizes DELLA proteins in Arabidopsis (bioRxiv)

The canonical model of gibberellic acid (GA) signaling pathway includes the recognition of the hormone by the receptor GID1 and the further degradation of the DELLA proteins by the proteasome. In this paper, Blanco-Touriñan et al. observed in Arabidopsis that the DELLA protein REPRESSOR OF ga1-3 (RGA) reduction under warm and shade conditions is independent of GA/GID1 mediated degradation. They found that this environmental degradation of RGA is mediated by the E3 ubiquitin ligase CONSTITUTIVELY PHOTOMORPHOGENIC1 (COP1). Moreover, the DELLA proteins RGA and GAI1 can directly interact with COP1 and SPA1 and be ubiquitinated. They also analyze the physiological relevance of this interaction, showing that in cop1 mutants, the defect in hypocotyl growth is dependent on DELLAs and can be rescued by adding exogenous GA. This work connects the DELLA proteins with COP1/SPA1, central regulators of light and temperature responses. The GA/GID1 pathway emerged in vascular plants, while DELLA and COP1 genes are present in all land plant lineages. This alternative regulation of DELLA stability could represent an ancient mechanism that explains the role of these proteins in other plant lineages. (Summary by Facundo Romani) bioRxiv 10.1101/2020.01.09.897157