SlSNAT2, a chloroplast-localized acetyltransferase, is involved in Rubisco lysine acetylation and negatively regulates drought stress tolerance in tomato

Drought stress seriously inhibits crop growth and yields and constrains photosynthesis, which is a key biological process. Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is a key enzyme in the carbon assimilation process, and while its activity is reportedly significantly inhibited under drought stress, little is known about the underlying molecular mechanism. We identified a chloroplast-localized acetyltransferase, SlSNAT2, negatively regulates drought tolerance in tomato. The slsnat2 mutants were conduced to endogenous abscisic acid accumulation in tomato and could promote scavenging of reactive oxygen species through the enhanced activity of antioxidant enzymes. Knocking out this gene could therefore improve photosynthesis under drought stress. Moreover, SlSNAT2 could catalyze the Lys acetylation of rbcL, a large Rubisco subunit. And SlSNAT2 knockout lines were found to maintain higher levels of Rubisco activity under drought stress in the absence of SlSNAT2-catalyzed acetylation of rbcL than wild type plants. Our results demonstrate that SlSNAT2 functions as a negative regulator of drought tolerance. Accordingly, SlSNAT2 could be targeted in molecular designs for tomato breeding.