BioProject

tRNAs are critical linker molecules that couple mRNA to protein translation and their availability is a limiting factor for translation. More...

tRNAs are critical linker molecules that couple mRNA to protein translation and their availability is a limiting factor for translation. tRNA transcription and the composition of the tRNA pool are both dynamically regulated in response to environmental cues. Recent work suggests that they also play an important role in regulating cell growth and differentiation. Toxoplasma gondii is a highly adaptable, early eukaryotic protozoan that is able to replicate in virtually any nucleated cell and many different host organisms, thus requiring fine-tuning of protein expression. A key feature of parasite pathogenesis is the ability to differentiate between fast growing tachyzoite and slow growing bradyzoite cyst forms, in response to stress e.g. nutrient starvation. Differentiation is accompanied by changes to the mRNA transcriptome and proteome but little is known about translational regulation. In this study, we used comparative genomics to catalogue the repertoire of tRNA genes in T. gondii and their genomic distribution. Interestingly, many tRNAs occur in regulatory regions and intronic sequences of protein-coding genes, which correlates with increased gene expression. To characterize the tRNA pool of T. gondii during stress and differentiation, we surveyed levels of precursor tRNA molecules in the tRNA population by small RNA-seq in three divergent parasite strains with varying bradyzoite differentiation competencies, cultured in normal or bradyzoite differentiation-inducing (pH shock) conditions. Almost all tRNA genes are constitutively transcribed in T. gondii tachyzoites and transcription of individual tRNA genes differs significantly between strains. The abundance of individual tRNAs in the tRNA pool reflects proteomic codon usage, suggesting that tRNA levels are tightly controlled according to the demands of translation. Together, this work suggests that modulation of the tRNA pool is a mechanism by which the protein landscape in T. gondii is regulated in different strains and developmental stages. Overall design: Three divergent Toxoplasma gondii strains were cultured in tachyzoite (pH7) or bradyzoite (pH8) growth conditions and subjected to small RNA-seq. Less...