The MATH-BTB BPM3 and BPM5 subunits of Cullin3-RING E3 ubiquitin ligases target PP2CA and other clade A PP2Cs for degradation

Abstract

Significance Relief of repression imposed by negative regulators is a crucial mechanism for plant hormone signaling. Clade A PP2Cs are key negative regulators of ABA signaling that are inhibited by ABA receptors. Degradation of PP2Cs is a complementary mechanism to PYR/PYL/RCAR-mediated ABA-dependent inhibition of PP2Cs. We reveal that BTB/POZ AND MATH DOMAIN proteins (BPMs), substrate adaptors of the multimeric cullin3 (CUL3)-RING-based E3 ligases (CRL3s), target PP2Cs for degradation. BPM-dependent degradation of PP2Cs is required for ABA-induced stomatal closure to counteract ABA-induced accumulation of PP2Cs and to reset resting phosphatase levels that allow efficient ABA signaling. Therefore, BPM-mediated proteolysis of transcription factors and clade A PP2Cs emerges as a general mechanism to regulate stress response and ABA signaling.