The ribosome-associated N-terminal acetyltransferase B coordinates global proteostasis and autophagy in plants by creating Ac/N-degrons

The N-terminal acetyltransferase B (NatB) acetylates ~20% of the eukaryotic proteome. However, the role of NatB-mediated N-terminal acetylation (NTA) for the regulation of the proteome fate remains unclear in eukaryotes. In this study, we demonstrate that CRISPR-Cas9-mediated deletion of NatB activity in plants results in significantly lowered global protein turnover due to decreased ubiquitin-proteasome system (UPS) activity and protein translation. Quantitative proteomics uncovers that NatB substrates are significantly enriched in the fraction of stabilized proteins in natb mutants. We provide direct evidence that the absent NTA of KIN11, a subunit of the autophagy-controlling energy sensor SnRK1, protects it from UPS-mediated destruction. The resulting accumulation of KIN11 is responsible for the increased resistance of natb mutants to energy limitation induced by prolonged darkness. Our findings establish NatB as a central regulator of UPS-autophagy interplay and highlight its role in maintaining proteome stability and enabling dynamic stress responses in plants.