An essential pentatricopeptide repeat protein in the apicomplexan remnant chloroplast

Abstract

The malaria parasite Plasmodium and other apicomplexans such as Toxoplasma evolved from photosynthetic organisms and contain an essential, remnant plastid termed the apicoplast. Transcription of the apicoplast genome is polycistronic with extensive RNA processing. Yet little is known about the mechanism of apicoplast RNA processing. In plants, chloroplast RNA processing is controlled by multiple pentatricopeptide repeat (PPR) proteins. Here, we identify the single apicoplast PPR protein, PPR1. We show that the protein is essential and that it binds to RNA motifs corresponding with previously characterized processing sites. Additionally, PPR1 shields RNA transcripts from ribonuclease degradation. This is the first characterization of a PPR protein from a nonphotosynthetic plastid.

Essential Genes of the Parasitic Apicomplexa

“…Plasmodium has two annotated PPR proteins, one of which is targeted to the apicoplast (PfPPR1; PF3D7_1406400/PBANKA_1035800) and the other does not have a clear targeting sequence for either the apicoplast or the mitochondria (PfPPR2; PF3D7_1233300/PBANKA_1448000/TGGT1_243530). Both are predicted to be highly essential in Plasmodium, and though PfPPR1 does not have a direct ortholog in T. gondii, T. gondii also appears to have a single apicoplast-targeted PPR protein (TGGT1_244050) that is essential for parasite growth (54). Using models based on plant PPR-proteins and the related algal octatricopeptide-repeat (OPR) proteins (which do not have annotated representatives in the Apicomplexa), Hillebrand and colleagues recently discovered a novel family of related proteins they termed heptatricopeptiderepeat (HPR) proteins that they then confirmed to localize to mitochondria and have specific RNA-binding capability (55).…”

Chloroplastic pentatricopeptide repeat proteins (PPR) in albino plantlets of Agave angustifolia Haw. reveal unexpected behavior

“…Within this group of proteins known as the nucleus-encoded RNA-binding proteins (RBPs) [ 9 ] are the mitochondrial transcription termination factor (mTERF) proteins [ 10 ], DEAD-Box RNA Helicases (RHs) [ 11 ], chloroplast ribonucleoproteins (cpRNPs) [ 12 ], pentatricopeptide repeat (PPR) proteins [ 13 ], and others. Within the variety of RBPs, PPR proteins are considered one of the most important players in post-transcriptional processes [ 14 , 15 ].…”