Jasmonate (JA) signaling in plants is mediated by the JASMONATE ZIM-DOMAIN (JAZ) proteins that repress the activity of several transcription factors regulating JA-inducible gene expression. The hormone JA-isoleucine triggers the interaction of JAZ repressor proteins with the F-box protein CORONATINE INSENSITIVE1 (COI1), part of a Skp1/Cullin1/F-box protein COI1 (SCFCOI1) E3 ubiquitin ligase complex, and their degradation by the 26S proteasome. In Arabidopsis thaliana, the JAZ family consists of 13 members. The level of redundancy or specificity amongst these members is currently not well understood. Here, we characterized JAZ12, encoded by a highly expressed JAZ gene. JAZ12 interacted with the transcription factors MYC2, MYC3 and MYC4 in vivo and repressed MYC2 activity. Using tandem affinity purification we found JAZ12 to interact with SCFCOI1 components, matching with observed in vivo ubiquitination and with rapid degradation after treatment with JA. In contrast to the other JAZ proteins, JAZ12 also interacted directly with the E3 RING ligase KEEP ON GOING (KEG), a known repressor of the ABSCISIC ACID INSENSITIVE5 (ABI5) transcription factor in abscisic acid (ABA) signaling. To study the functional role of this interaction, we circumvented the lethality of keg loss-of-function mutants by silencing KEG using an artificial microRNA approach. ABA treatment promoted JAZ12 degradation and KEG knock-down led to a decrease in JAZ12 protein levels. Correspondingly, KEG overexpression was capable of partially inhibiting COI1-mediated JAZ12 degradation. Our results provide additional evidence for KEG as an important factor in plant hormone signaling and a positive regulator of JAZ12 stability.