SUMO ylation represses SnRK 1 signaling in Arabidopsis

Summary

The SnRK 1 protein kinase balances cellular energy levels in accordance with extracellular conditions and is thereby key for plant stress tolerance. In addition, SnRK 1 has been implicated in numerous growth and developmental processes from seed filling and maturation to flowering and senescence. Despite its importance, the mechanisms that regulate SnRK 1 activity are poorly understood. Here, we demonstrate that the SnRK 1 complex is SUMO ylated on multiple subunits and identify SIZ 1 as the E3 Small Ubiquitin‐like Modifier (SUMO ) ligase responsible for this modification. We further show that SnRK 1 is ubiquitinated in a SIZ 1‐dependent manner, causing its degradation through the proteasome. In consequence, SnRK 1 degradation is deficient in siz1‐2 mutants, leading to its accumulation and hyperactivation of SnRK 1 signaling. Finally, SnRK 1 degradation is strictly dependent on its activity, as inactive SnRK 1 variants are aberrantly stable but recover normal degradation when expressed as SUMO mimetics. Altogether, our data suggest that active SnRK 1 triggers its own SUMO ylation and degradation, establishing a negative feedback loop that attenuates SnRK 1 signaling and prevents detrimental hyperactivation of stress responses.