Codon biased translation mediated by Queuosine tRNA modification is essential for the virulence of Leishmania mexicana

The complex life cycle of the human parasite Leishmania mexicana requires rapid translational adaptation for survival in two distinct environments: the insect vector and the mammalian host. These medically important protists lack conventional transcriptional control due to their unusual genome organization. Consequently, tRNA modifications may provide an additional mechanism for post-transcriptional regulation of gene expression. One such modification is queuosine (Q), which is incorporated at anticodon wobble position 34 of specific tRNAs. Here, we demonstrate that Q-tRNA levels increase substantially during Leishmania differentiation from the insect stage to the mammalian-infective stage. Mutant cells lacking the enzyme responsible for Q incorporation, tRNA-guanine transglycosylase (TGT), exhibit substantial changes in the proteome during differentiation in vitro . Specifically, downregulated proteins were enriched in NAU codons, whereas upregulated proteins predominantly contained NAC codons. We further evaluated the effect of Q-tRNA depletion on macrophage infections and using mouse model. Although LmxTGT2 knockout parasites exhibited normal growth and differentiation in vitro , they demonstrated impaired survival within macrophages and reduced pathogenicity in mice. Taken together, these results highlight the critical role of Q-tRNA modification in maintaining translational balance and reveal a novel level of gene expression regulation facilitating parasite adaptation to changing environments and contributing to Leishmania virulence.