Hormone-mediated disassembly and inactivation of a plant E3 ubiquitin ligase complex.

Phytohormone abscisic acid (ABA) regulates key plant development and environmental stress responses. The ubiquitin-proteasome system tightly controls ABA signaling. CULLIN4-RING (CRL4) E3 ubiquitin ligases use the substrate receptor module CONSTITUTIVELY PHOTOMORPHOGENIC1 (COP10)-DDB1-DET1-DDA1 (CDDD) to target Arabidopsis ABA receptor PYL8, acting as negative regulators of ABA responses. Conversely, ABA treatment attenuates PYL8 receptor degradation, although the molecular mechanism remained elusive. Here, we show that ABA promotes the disruption of CRL4-CDDD complexes, leading to PYL8 stabilization. ABA-mediated CRL4-CDDD dissociation likely involves an altered association between DDA1-containing complexes and the COP9 signalosome (CSN), a master regulator of the assembly of cullin-based E3 ligases, including CRL4-CDDD. Indeed, treatment with CSN inhibitor CSN5i-3 suppresses the ABA effect on CRL4-CDDD assembly. Our findings indicate that ABA stabilizes PYL8 by altering the dynamics of the CRL4-CDDD-CSN complex association, showing a regulatory mechanism by which a plant hormone inhibits an E3 ubiquitin ligase to protect its own receptors from degradation.