SnRK2.6-mediated phosphorylation stabilizes proteasome regulator 1 (PTRE1) to enhance 26S proteasome activity and coordinate ABA signaling in Arabidopsis

Abscisic acid (ABA) regulates diverse aspects of plant growth, particularly adaptive responses to abiotic stress. Although the ubiquitin-proteasome system is recognized as a pivotal pathway for degrading key components of ABA signaling, the mechanisms governing 26S proteasome activity during ABA responses remain largely unclear. Here, we show that Arabidopsis proteasome regulator 1 (PTRE1) modulates ABA signaling by regulating proteasome activity. Phenotypic analyses reveal heightened ABA sensitivity in the ptre1 mutant. Mechanistically, ABA stabilizes the PTRE1 protein, thereby enhancing 26S proteasome activity. Sucrose nonfermenting 1-related kinase 2.6 (SnRK2.6), a key kinase activated by ABA, directly interacts with and phosphorylates PTRE1, which is essential for PTRE1 stability and its function in ABA responses. Notably, loss of PTRE1 leads to increased accumulation of the ABA-insensitive 5 (ABI5) protein, and the ptre1 mutation partially suppresses the ABA-insensitive phenotype of the abi5 mutant. Collectively, these findings establish an SnRK2.6-PTRE1 module that fine-tunes proteasome activity, providing new insights into the coordinated regulation of ABA signaling through SnRK2.6-mediated dual phosphorylation of ABI5 and PTRE1.