mRNA pseudouridylation affects RNA metabolism in the parasite Toxoplasma gondii

RNA contains over 100 modified nucleotides that are created post-transcriptionally, among which pseudouridine (Psi) is one of the most abundant. Although it was one of the first modifications discovered, the biological role of this modification is still not fully understood. Recently, we reported that a pseudouridine synthase (TgPUS1) is necessary for differentiation of the single-celled eukaryotic parasite Toxoplasma gondii from active to chronic infection. To better understand the biological role of pseudouridylation, we report here gel-based and deep-sequencing methods to identify TgPUS1-dependent Psi's in Toxoplasma RNA, and the use of TgPUS1 mutants to examine the effect of this modification on mRNAs. In addition to identifying conserved sites of pseudouridylation in Toxoplasma rRNA, tRNA, and snRNA, we also report extensive pseudouridylation of Toxoplasma mRNAs, with the Psi's being relatively depleted in the 3'-UTR but enriched at position 1 of codons. We show that many Psi's in tRNA and mRNA are dependent on the action of TgPUS1 and that TgPUS1-dependent mRNA Psi's are enriched in developmentally regulated transcripts. RNA-seq data obtained from wild-type and TgPUS1-mutant parasites shows that genes containing a TgPUS1-dependent Psi are relatively more abundant in mutant parasites, while pulse/chase labeling of RNA with 4-thiouracil shows that mRNAs containing TgPUS1-dependent Psi have a modest but statistically significant increase in half-life in the mutant parasites. These data are some of the first evidence suggesting that mRNA Psi's play an important biological role.