Malaria pathogenesis results from the asexual replication of Plasmodium falciparum within human red blood cells, which relies on a precisely timed cascade of gene expression over a 48-h life cycle. Although substantial post-transcriptional regulation of this hardwired program has been observed, it remains unclear how these processes are mediated on a transcriptome-wide level. To this end, we identified mRNA modifications in the P. falciparum transcriptome and performed a comprehensive characterization of N 6-methyladenosine (m 6 A) over the course of blood-stage development. Using mass spectrometry and m 6 A RNA sequencing, we demonstrate that m 6 A is highly developmentally regulated, exceeding m 6 A levels known in any other eukaryote. We characterize a distinct m 6 A writer complex and show that knockdown of the putative m 6 A methyltransferase, PfMT-A70, by CRISPR interference leads to increased levels of transcripts that normally contain m 6 A. In accordance, we find an inverse correlation between m 6 A methylation and mRNA stability or translational efficiency. We further identify two putative m 6 Abinding YTH proteins that are likely to be involved in the regulation of these processes across the parasite's life cycle. Our data demonstrate unique features of an extensive m 6 A mRNA methylation programme in malaria parasites and reveal its crucial role in dynamically fine-tuning the transcriptional cascade of a unicellular eukaryote.

Background Quiescence is an unconventional mechanism of Plasmodium survival, mediating artemisinin resistance. This phenomenon increases the risk of clinical failures following artemisinin-based combination therapies (ACTs) by slowing parasite clearance and allowing the selection of parasites resistant to partner drugs. Objectives To thwart this multiresistance, the quiescent state of artemisinin-resistant parasites must be taken into consideration from the very early stages of the drug discovery process. Methods We designed a novel phenotypic assay we have named the quiescent-stage survival assay (QSA) to assess the antiplasmodial activity of drugs on quiescent parasites. This assay was first validated on quiescent forms from different artemisinin-resistant parasite lines (laboratory strain and field isolates), using two reference drugs with different mechanisms of action: chloroquine and atovaquone. Furthermore, the efficacies of different partner drugs of artemisinins used in ACTs were investigated against both laboratory strains and field isolates from Cambodia. Results Our results highlight that because of the mechanism of quiescence and the respective pharmacological targets of drugs, drug efficacies on artemisinin-resistant parasites may be different between quiescent parasites and their proliferating forms. Conclusions These data confirm the high relevance of adding the chemosensitivity evaluation of quiescent parasites by the specific in vitro QSA to the antiplasmodial drug development process in the current worrisome context of artemisinin resistance.