Protein arginine methyltransferase 5 is essential for virulence in Toxoplasma gondii

Protein arginine methyltransferase 5 (PRMT5) is a key enzyme responsible for catalyzing symmetric dimethylarginine (SDMA) modifications and plays crucial roles in epigenetic regulation, transcription, and cell cycle progression in eukaryotes. Although our previous study determined the expression and cellular localization of PRMT5 in tachyzoites and bradyzoites, and confirmed its type II PRMT activity, its functional significance in Toxoplasma gondii remains entirely uncharacterized.

This study aimed to explore the biological functions of PRMT5 in T. gondii. The prmt5 gene was disrupted in the type I RH strain using the clustered regularly interspaced short palindromic repeats (CRISPR) Cas9 system. The biological roles of PRMT5 were evaluated via multiple functional assays, including plaque formation, intracellular proliferation, host cell invasion, virulence, and tachyzoite to bradyzoite conversion assays. RNA sequencing was further performed to profile transcriptomic alterations induced by prmt5 disruption.

Phenotypic characterization revealed that the ∆prmt5 strain exhibited reduced symmetric dimethylarginine (SDMA) levels as well as severe defects in plaque formation, invasion, intracellular replication, and bradyzoite differentiation. Accordingly, the virulence of the ∆prmt5 strain was dramatically attenuated, as all infected BALB/c mice survived over a 10-day period, in stark contrast to the 100% mortality observed in the wild-type control group within 10 days. RNA-sequencing analysis uncovered the molecular basis for these phenotypes, demonstrating that prmt5 disruption leads to global transcriptional dysregulation. Specifically, we identified a significant downregulation of genes associated with motor protein function and fatty acid metabolism pathways.

Our research has demonstrated that PRMT5 plays a critical role in the proliferation, survival, pathogenicity, and regulation of gene expression in Toxoplasma gondii.