Stress-induced regulation of N-terminal acetylation controls proteostasis in plants

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Growth of plants is limited by environmental factors and corresponding cellular surveillance mechanisms for stress-induced damage repair. The control of protein homeostasis is a major player in the acclimation of the proteome to specific stresses and the replacement of damaged proteins. In this project, the role of the co-translational modification of proteins by N-acetyltransferase (Nat) complexes for acclimation to stress will be investigated. N-terminal acetylation by the major NatA complex affects about 40% of all cytosolic proteins in Arabidopsis with significant effects on their half-life time. Based on the observation that the drought stress hormone abscisic acid (ABA) decreases NatA activity in Arabidopsis, causing faster translation and more efficient degradation of non-acetylated NatA substrates by a novel nonAc/N-degron, we propose that lowered N-terminal acetylation serves as a signal enabling efficient replacement of stress-damaged proteins This novel protein-imprinted stress-transducing signal may generally operate in protein-damaging stress responses. Using drought stress as a proxy, we will dissect the roles of the core and regulatory subunits of the NatA complex for stress-induced protein imprinting at the ribosome. ABA-induced down-regulation of NatA activity will be applied to identify stress-regulated NatA substrates and study the dynamic recruitment of the NatA complex to the ribosome nascent chain complex using selective ribosome profiling. The turnover of ABA-triggered nonAc/N-degron containing proteins can be quantified by in vivo imaging using the tandem fluorescent timer system. The fate of nonAc/N-degron containing proteins is going to be dissected with respect to ubiquitin-proteasome and autophagy-mediated degradation following affinity-based enrichment and protein mass spectrometry. Finally, the role of the sensor kinase TOR for enhanced translation in situations with lowered NatA activity will be assessed. The proposed experiments are expected to clarify the significance and mechanism of action of dynamic N-terminal acetylation for proteostasis under protein-damaging stress.