Loss of an uncharacterized mitochondrial methionine tRNA-synthetase induces mitochondrial unfolded protein response in .

Aminoacyl-tRNA synthetases (aaRSs) are essential for translation, as they charge tRNA molecules with their corresponding amino acids. Alterations in aaRSs can significantly disrupt both cytosolic and mitochondrial translation. Through a forward genetic screen for mitochondrial unfolded protein response (UPR) activators in , we identified a missense mutation (P447V) in the previously uncharacterized gene Y105E8A.20, which encodes a dually localized methionine tRNA synthetase (MetRS). Here, we characterize the UPR induction by Y105E8A.20, which we call , and demonstrate that the P447V allele is a loss-of-function mutation. Furthermore, we show impaired activity in the mitochondria triggers UPR. This strain provides a valuable tool for studying mitochondrial translation and understanding how aaRSs are involved in mitochondrial homeostasis.