TGN/EE SNARE protein SYP61 is ubiquitinated and required for carbon/nitrogen-nutrient responses in Arabidopsis

Ubiquitination is a post-translational modification with reversible attachment of the small protein ubiquitin, which is involved in numerous cellular processes including membrane trafficking. For example, ubiquitination of cargo proteins is known to regulate their subcellular dynamics, and plays important roles in plant growth and stress adaptation. However, the regulatory mechanism of the trafficking machinery components remains elusive. Here, we report Arabidopsis trans-Golgi network/early endosome (TGN/EE) localized soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNARE) protein SYP61 as a novel ubiquitination target of a membrane localized ubiquitin ligase ATL31. SYP61 is a key component of membrane trafficking in Arabidopsis. SYP61 was ubiquitinated with K63-linked chain by ATL31 in vitro and in plants. The knockdown mutants of SYP61 were hypersensitive to the disrupted carbon (C)/nitrogen (N)-nutrient stress, suggesting its critical role in plant homeostasis in response to nutrients. We also found the ubiquitination status of SYP61 is affected by C/N-nutrient availability. These results provided possibility that ubiquitination of SNARE protein has important role in plant physiology.