Role of <i>Arabidopsis</i> monomeric E3 ubiquitin ligases in the ABA signaling pathway

Abscisic acid (ABA) is a key phytohormone that regulates multiple biological processes in plants, including seed germination, seedling growth, and abiotic stress response. ABA enhances drought tolerance by promoting stomatal closure, thereby improving crop productivity under unfavorable stress conditions. Extensive research efforts have focused on understanding ABA signaling more clearly for its potential application in agriculture. The accumulation and stability of signaling components involved in the efficient transduction of downstream ABA signaling are affected by both transcriptional regulation and post-translational modifications. Ubiquitination is a representative post-translational modification that regulates protein stability, and E3 ubiquitin ligase is a key enzyme that determines target substrates for ubiquitination. To date, many E3 ligases functioning as a monomeric form such as RING-, HECT- and U-box-types have been known to participate in the ABA signaling process. In this review, we summarize the current understanding of ABA-related monomeric E3 ligases, their regulation, and mode of action in Arabidopsis, which will help develop a detailed and integrated understanding of the ABA signaling process in Arabidopsis.