Chloroplastic Aspartyl‐tRNA Synthetase Is Required for Chloroplast Development, Photosynthesis and Photorespiratory Metabolism

ABSTRACT Photorespiration is a complex metabolic process linked to primary plant metabolism and influenced by environmental factors, yet its regulation remains poorly understood. In this study, we identified the asprs3‐1 mutant, which displays a photorespiratory phenotype with leaf chlorosis, stunted growth, and diminished photosynthesis under ambient CO 2 , but normal growth under elevated CO 2 conditions. Map‐based cloning and genetic complementation identified AspRS3 as the mutant gene, encoding an aspartyl‐tRNA synthetase. AspRS3 is localised in both chloroplasts and mitochondria, with the chloroplast being the primary site of its physiological function. The AspRS3 mutation impacts the expression of plastid‐encoded and photosynthesis‐related genes, leading to decreased levels of chloroplast‐encoded proteins such as ribulose‐1,5‐bisphosphate carboxylase/oxygenase large subunit (RBCL) and ferredoxin‐dependent glutamate synthase (Fd‐GOGAT). Furthermore, we observed an accumulation of photorespiratory intermediates, including glycine and glycerate, and reactive oxygen species (ROS) in asprs3‐1 . However, under high CO 2 , the expression of these proteins, the accumulation of photorespiratory intermediates, and ROS levels in asprs3‐1 did not significantly differ from those in the wild type. We propose that elevated CO 2 mitigates the asprs3‐1 phenotype by inhibiting Rubisco oxygenation and photorespiratory metabolism. This study highlights the role of aminoacyl‐tRNA synthetases in regulating photorespiration and provides new insights into its metabolic control.