A non-enzymatic acetylation of lysine residues adversely affects the Rubisco activase protein stability

The post-translational modifications of non-histone (PTMs) proteins functions are crucial for the plant adaption to the changing environment. The Rubisco activase (RCA) plays a key role in the CO2 fixation through the Rubisco activation process. We reported that the RCA from tobacco leaf could be acetylated at several lysine residues including K126 and K164. The acetylation level changes under different light conditions (night and day) as well as under heat stress (45 {degrees}C). We further showed that the RCA can be non-enzymatically acetylated in vitro, especially by the acetyl-CoA (Ac-CoA) through direct interaction between them. Our results of the in vitro assay with deuterium labeled Ac-CoA (D2-Ac-CoA) show that the two conserved RCA lysine residues (K126 and K164) were acetylated by Ac-CoA, entraining a dramatic decline in its ATPase activity and a slight effect on the Rubisco activation process. Furthermore, we revealed that the higher RCA acetylation level induced its faster degradation in the chloroplast, which was not a direct consequence of ubiquitination. Eventually, our findings unraveled a new prominent role for the protein acetylation in modulating the RCA stability, which could certainly regulate the carbon assimilation efficiency towards a different energy status of the plants.