Potential roles of tRNA modifications in the human malaria parasite plasmodium falciparum
Ng, Chee Sheng
Date of Issue2016
School of Biological Sciences
Singapore-MIT Alliance for Research and Technology, Massachusetts Institute of Technology
Poor correlation of mRNA and protein levels suggests a role for translational control of gene expression during the Plasmodium intra-erythrocytic life cycle. Among the components of translational machinery, the dozens of ribonucleoside modifications on transfer RNAs (tRNA) are emerging as critical regulators of cell physiology and stress response. However, little is known about malaria tRNA modifications and their roles in gene expression, making it an unexplored area of Plasmodium translational biology. We have now characterized the repertoire of tRNA modifications of P. falciparum and identified critical functions in tRNA maturation and stage-specific translation. Remarkably, P. falciparum has a standard set of eukaryotic tRNA modifications that resembles the model organism Saccharomyces cerevisiae. We demonstrated that these modifications are tightly regulated in two ways throughout the intra-erythrocytic developmental cycle (IDC) of the parasite. First, we observed a synchronized increase in most of the modifications from ring to trophozoite stage, suggesting tRNA maturation to meet stage-dependent translational needs of the parasite. To better understand the relevance of these changes in modifications, we then performed iTRAQ proteomics to quantify the protein abundances across the IDC. Strikingly, the most abundantly expressed proteins in the late stage of the IDC, but not early stages, have a marked codon bias that can be directly correlated with the corresponding increase in tRNA modifications. Based on these results, we propose a new model for how tRNA modifications govern the late-stage of the malaria IDC by controlling the abundance of stage-specific proteins through facilitating selective translation of codon-biased transcripts. In parallel, we examined the involvement of tRNA modifications in stress-induced translational control by treating the parasites with IC20-90 doses of hydrogen peroxide, artemisinin and chloroquine. Hierarchical clustering and principal component analysis distinguished signature tRNA modifications reprogramming patterns induced by different stresses, implying stress-specific translational control mechanism for survival response. These findings together provide new insights into the translational control mechanisms in the development, pathogenesis, and stress response of Plasmodium parasites.