Dr. Markus Wirtz, University of Heidelberg

As sessile organisms, plants have to fight environmental challenges on site. Their ability to adapt to changing conditions relies heavily on the proteome's dynamic plasticity, which enables rapid, coordinated cellular responses.

Central to this adaptability is proteostasis, the maintenance of protein homeostasis through the tightly regulated processes of protein synthesis, folding, post-translational modification, and degradation. Although protein degradation plays a critical role in determining cellular fate, the mechanisms by which proteostasis is regulated in plants under both stress conditions and favorable growth environments remain incompletely understood.

Post-translational modifications have emerged as key determinants of protein stability in eukaryotic systems and are subject to extensive regulation during plant stress responses. Increasing evidence indicates that crucial decisions governing protein fate occur co-translationally. As nascent polypeptide chains emerge from the ribosomal exit tunnel, they are immediately engaged by ribosome-associated factors that influence their folding trajectory, the acquisition of specific N-terminal modifications, and, if necessary, their targeting for quality control and degradation pathways.

Among these modifications, N-terminal acetylation represents one of the most prevalent co-translational processes in eukaryotes. This modification is catalyzed by a family of evolutionarily conserved enzymes known as N-terminal acetyltransferases (NATs), whose substrate specificity is largely determined by the identity of the first few amino acids at the protein N-terminus.

This presentation will provide an overview of the N-terminal acetylation machinery in higher plants. Of the seven identified NAT complexes (NatA-NatG), NatA and NatB constitute the predominant forms, associating with ribosomes to co-translationally acetylate approximately 60% of the proteome. Particular emphasis will be placed on the roles of NatA and NatB in plant stress responses, as well as on their distinct contributions to the regulation of global proteostasis.