The role of protein acetylation in the regulation of photosynthetic light reactions.

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The photosynthetic electron transport has to be dynamically regulated in dependence on environmental conditions to prevent photoinhibition and photodamage of the photosystems. Several chemical modifications of proteins are known to play important roles in modulating photosynthetic yield during plant acclimation responses. Next to phosphorylation, the acetylation of amino groups within proteins is a major posttranslational modification in all organisms and is particularly abundant on proteins involved in photosynthesis. N-terminal acetyltransferases or lysine acetyltransferases catalyze the transfer of the acetyl group from acetyl coenzyme A to the targeted amino group. In contrast to N-terminal acetylation, the acetylation of lysine residues (KAc) is reversible, whereby lysine deacetylases are responsible for the removal of acetyl groups from proteins. Recently, we identified eight new dual-specific acetyltransferases (GNTAs) in chloroplasts of Arabidopsis. The first characterization of GNAT2 revealed that this enzyme is indispensable for photosynthetic state transitions. In addition, the mutants show increased energy-dependent quenching at high light intensities compared to WT. While the first protein substrates of GNAT2 have been identified, the specific role of protein acetylation in the acclimation responses of the photosynthetic light reactions is still not understood on a mechanistic level. This project will provide novel biochemical insights into the functions of acetylation on selected target proteins, as well as the involvement of the closely related Arabidopsis plastidial acetyltransferases GNAT1-3 in regulating protein acetylation of photosynthetic proteins involved in energy-dependent quenching (see also Graphical Abstract P9). Latest in gel chemical crosslinking techniques will be used to study differences in thylakoid protein complex composition in dependence on light and genotype, which will be combined with electron cryotomography for 3D constructions. Specifically, we will focus on the role of acetylation in the photosynthetic acclimation responses to changes in light availability. This project will deliver on Aim 4 of GoPMF and contribute to GoPMF Aims 1, 2 and 3.