Emerging Functions for N-Terminal Protein Acetylation in Plants

Abstract

N-terminal (Nt-) acetylation is a widespread but poorly understood co-translational protein modification. Two reports now shed light onto the proteome-wide dynamics and protein-specific consequences of Nt-acetylation in relation to plant development, stress-response, and protein stability, identifying this modification as a key regulator of diverse aspects of plant growth and behaviour.

Keywords: N-end rule; N-terminal acetylation; abscisic acid (ABA); drought stress; plant immunity; protein degradation.

Figure 1

Recently Identified Functions for N-Terminal (Nt) Acetylation in Plants. (A) Under normal conditions NATA co-translationally Nt-acetylates (Ac) a large number of proteins following Nt-Met excision . Drought-induced abscisic acid (ABA) accumulation (green gradated triangle) depletes NATA transcript and protein abundance, which leads to a global reduction in the number of Nt-acetylated proteins, resulting in several adaptive responses that improve drought-tolerance and survival . Thus, NATA-mediated Nt-acetylation is proposed to act as an important switch coordinating metabolic, developmental and physiological responses downstream of ABA. (B) The Nod-like receptor protein SNC1 plays a key role in plant immunity. Two Nt-variants of SNC1 are present in plants, most likely arising as a result of alternative translation. Nt-Met-Met-Asp-SNC1 (MMD-) is Nt-acetylated by NATA, whereas Nt-Met-Asp-SNC1 (MD-), which lacks the first Met residue, is Nt-acetylated by NATB . Remarkably, these Nt-acetylation events have contrasting consequences, destabilising or stabilising SNC1, which decreases or enhances the immune response, respectively. Xu et al. suggest that Nt-acetylation of these alternate Nt-isoforms contributes to overall SNC1 homeostasis. This study reveals that different NAT complexes can have antagonistic effects on the stability of a protein depending on the nature of its N-terminus, suggesting that: (i) control of protein half-life by Nt-acetylation is more complex than previously postulated , and; (ii) that the previously identified acetylation-dependent branch of the N-end rule pathway (the Ac/N-end rule) may be functional in plants .