Transcriptional changes in Plasmodium falciparum asexual stages upon knock down of mitochondrial ribosomal proteins RSM22 and L23

Mitoribosomes are assembled via multistep processes to translate proteins encoded in the mitochondrial (mt) genome. Plasmodium mitoribosomes are composed of unusually fragmented ribosomal RNA (rRNA) encoded in the mitochondrial (mt) DNA. All mitoribosomal proteins (MRPs) and other assembly factors are encoded in the nuclear genome. Here, we have studied one small subunit (SSU) MRP, RSM22 (Pf3D7_1027200) and one large subunit (LSU) MRP, L23 (Pf3D7_1239100) in Plasmodium falciparum. We show that both of these proteins localize to the mitochondrion and are essential for parasite survival. However, the parasites survive conditional knock down (KD) of PfRSM22 for two days longer than PfMRPL23 KD. RNA sequencing has revealed major metabolic pathways affected by the absence of these MRPs at early and late timepoints post KD. Our data suggest that PfRSM22 plays a role in the assembly of mitoribosomes due to downregulation of fragmented rRNA and other putative MRPs by as early as day 2 KD. Contrary to that, some mt rRNA fragments are upregulated on day 2 post PfMRPL23 KD and PfMRPs. Analysis of later timepoints show that PfMPRL23 KD causes defects in essential metabolic pathways by day 4, leading to parasite death. We observed significant overlap among the mitochondrial related transcripts downregulation on day 4 PfMRPL23 KD and day 6 PfRSM22 KD. Via in-silico structural similarity prediction analysis, we have identified a number of proteins of unknown functions among the observed differentially regulated mitochondrial proteins that are potential lineage specific Plasmodium MRPs.