Co-translational control of protein stability and quality in plants

Proteostasis relies on the coordinated control of protein synthesis, folding, modification and degradation, and an increasingly clear picture is emerging that many important decisions governing protein fate occur co-translationally. As nascent chains first appear at the ribosome exit tunnel, they encounter a suite of ribosome-associated enzymes that begin to shape whether proteins fold productively, acquire the correct N-terminal imprinting modifications, or require surveillance and removal. This review focuses on two major facets of co-translational control that determine protein and proteome stability, with particular attention to recent advances in plants. First, N-terminal (Nt-) methionine excision, Nt- acetylation and Nt-myristoylation are examined as early imprinting steps that define the chemical identity and regulatory trajectories of newly synthesized proteins, including how they influence targeting to N-degron pathways of proteolysis. Second, ribosome-associated quality control (RQC) pathways that sense ribosome stalling or collision are outlined, along with their roles in directing aberrant nascent chains towards ubiquitylation, extraction and degradation before they can accumulate and trigger proteotoxic stress. Together, these modification and surveillance mechanisms form an integrated decision-making network that establishes protein stability at the earliest stages of synthesis, contributing to proteostasis and impacting plant growth, development, and stress adaptation.