The <scp>E3</scp> ubiquitin ligase <scp>OsPUB9</scp> modulates the abscisic acid signaling complex in response to cold stress in rice

Cold stress is a major abiotic stress factor that affects plant growth and development, leading to yield loss. Abscisic acid (ABA) plays important roles in mediating abiotic stress tolerance. The molecular mechanisms underlying crosstalk between cold tolerance and ABA signaling remain elusive. Here, we report the E3 ubiquitin ligase OsPUB9 as a critical regulator linking ABA signaling and cold stress response in rice. We demonstrate that OsPUB9 negatively regulates cold tolerance. Cold induces OsPUB9 expression, which promotes the degradation of OsICE1, a key transcription factor in cold signaling, thereby suppressing the expression of OsCBFs. Intriguingly, OsCBF3 binds the OsPUB9 promoter, establishing a feedback loop that upregulates OsPUB9 under cold stress to fine-tune OsICE1 stability. ABA induces OsPUB9 degradation whereas OsPUB9 modulates ABA signaling by ubiquitinating and degrading the phosphatase OsABI2 and the kinase SAPK10, which form a regulatory complex. OsPUB9 disrupts OsABI2-mediated dephosphorylation of SAPK10, enhancing SAPK10 activity. SAPK10 phosphorylates OsICE1, further linking ABA and cold pathways. Our results elucidate a dual role for OsPUB9 in balancing ABA signaling and cold response through posttranslational regulation of OsABI2, SAPK10, and OsICE1, offering novel targets for breeding climate-resilient rice varieties.