Biology subjects

Waller, R. F.

Publications and source records attributed to Waller, R. F..

At least 19 recordsLinked to original sources

bioRxiv2026

Helical Repeat Protein mRSiC is Required for rRNA Fragment Accumulation in T. gondii Mitochondria

Myzozoans, including apicomplexan parasites, possess highly reduced and unusual mitochondrial genomes that encode two to three respiratory chain subunits and extensively fragmented rRNAs forming a divergent mitoribosome. Heptatricopeptide repeat (HPR) proteins are expanded in myzozoans, with some functioning as mitoribosomal constitutes. Additional HPR proteins have been proposed to function in post-transcriptional processes of mitochondrial gene expression, though their specific roles remain unexplored. We present a phylogenetic analysis of HPR proteins that reveals extensive lineage-specific expansions, consistent with diversifications of mitochondrial gene expression systems within myzozoans. We further characterize mRSiC, a coccidian-specific HPR found in Toxoplasma gondii and its closest relatives. Using sRNA sequencing and RNA gel blot analyses, we show that mRSiC is required for the stabilization of two coccidian-specific mitochondrial sRNAs, RNA33 and RNA42. Loss of mRSiC causes rapid depletion of these RNAs, followed by secondary reductions of rRNA fragments, defects in the respiratory chain, and impaired parasite proliferation. Together, these findings highlight the importance of HPRs in apicomplexan mitochondrial gene expression and illustrate how lineage-specific RNA-binding factors support highly derived mitochondrial expression systems.

molecular biology↗

bioRxiv2025

Characterisation of Two Plasmodium Virulence Factors Important for Lipid Metabolism and Disease Progression In Vivo

Malaria is caused by Plasmodium parasites and claims 610,000 deaths annually. Parasite invasion of red blood cells (RBCs) involves secretion of multiple proteins from specialised apical organelles (micronemes, rhoptries, and dense granules). These collectively facilitate host cell entry, establish a protective parasitophorous vacuole (PV), and directly and indirectly mediate interactions between the infected RBC (iRBC) and the endothelial wall. The cytoadherence of iRBCs results in sequestration within organs and plays a critical role in pathogenesis and virulence, but the function of many secreted parasite proteins remains poorly characterised. Here, we leverage spatial proteomics from Plasmodium falciparum to identify two novel Plasmodium berghei orthologue proteins containing hydrolase domains (MAP1, PBANKA_1425900, and RhoSH, PBANKA_1001500). Ultrastructure expansion microscopy reveals their localisation to the rhoptries in late schizogony, where co-immunoprecipitation assays show they interact with each other. In vivo studies demonstrate that these proteins help the parasite evade spleen-mediated clearance and contribute to disease progression. Deletion of both genes disrupts lipid metabolism and PV membrane morphology, suggesting a role in establishing or maintaining the protective PV membrane. Loss of map1 reduces sequestration of P. berghei iRBCs to adipose tissue, and conditional knockdown of the P. falciparum map1 orthologue results in reduced CD36-mediated cytoadhesion, suggesting a cross-species role in sequestration and cytoadherence. Our findings identify MAP1 and RhoSH as key mediators of Plasmodium virulence.

microbiology↗

bioRxiv2025

The spatial proteome of the Plasmodium falciparum schizont illuminates the composition and evolutionary trajectories of its organelles

Malaria is caused by apicomplexan parasites of the genus Plasmodium, with all malaria symptoms and pathology caused by parasite stages that develop within, or transit between, host erythrocytes. The ability of Plasmodium cells to parasitise erythrocytes depends on distinctive intracellular compartments associated with invasion, as well as the development of unique cellular niches within the infected host cell. However, our understanding of the biology of the malaria parasite is limited by the fact that a large proportion of the parasites proteome has no known cellular location or function. To address this problem, we have generated comprehensive high-resolution maps of protein subcellular localisation for the invasive stage of the erythrocytic life cycle of Plasmodium falciparum, the major cause of malaria mortality. Using the spatial proteomics technique hyperplexed Localisation of Organelle Proteins by Isotopic Tagging (hyperLOPIT) we generated data for 3000 P. falciparum proteins expressed in late schizont stages. Our hyperLOPIT data resolved 24 distinct cellular niches, and using supervised machine-learning we can classify 1646 proteins into one of these compartments including exported sites within the host cell. Through comparative genomic analyses our data resolve the spatial patterns of cell evolution that have shaped the development of Plasmodium species and ongoing adaptive pressures and responses that challenge our efforts to manage these major disease-causing organisms.

microbiology↗

bioRxiv2024

Characterisation of cell cycle checkpoint kinases in Toxoplasma gondii

Toxoplasma gondii is a protozoan parasite in the apicomplexan phylum. Apicomplexan parasites replicate using a variety of non-canonical cell division modes, distinct from binary fission, whose molecular regulation is incompletely understood. T. gondii replicates by endodyogeny in its intermediate hosts, and by endopolygeny in its definitive host. To improve our understanding of how these unusual, flexible cell division modes are regulated, we characterised the T. gondii homologues of the cell-cycle checkpoint kinases ATM and ATR. These phosphoinositol-3-kinase-like kinases are entirely absent in some related parasites including Plasmodium; in T. gondii they are present but their putative checkpoint roles were previously uncharacterised. Both TgATM and TgATR were found to be dispersed throughout the parasite, rather than restricted to the nucleus, and they did not detectably relocate to the nucleus after DNA damage. Nevertheless, they were both required for checkpoint responses to DNA damage, including acute replication slowing and phosphorylation of the DNA damage marker histone H2AX. Unusually, the two kinases seemed to cooperate in the checkpoint response, with the loss of either one largely ablating the response, regardless of the type of DNA damage. Thus, T. gondii clearly retains a DNA-damage-responsive checkpoint, but some of its key features differ from the well-studied checkpoint in human cells. AUTHOR SUMMARYToxoplasma is one of the most widespread parasites of humans, with a large proportion of the global population being infected. Infection usually causes no symptoms, but can have severe consequences in pregnant women and immunocompromised people. The Toxoplasma parasite is a single-celled organism, related to other parasites that cause important human diseases like malaria. All these parasites are distinctive in having unusual modes of replication: unlike human cells, they do not replicate by simply splitting in two. Furthermore, drugs to treat toxoplasmosis usually act to suppress the parasites replication. Therefore, it is important to understand how this unusual replication is controlled, both for our fundamental understanding of cell division modes, and to ensure effective drug treatment of toxoplasmosis. Here, we characterised for the first time the proteins that control the Toxoplasma cell cycle by responding to DNA damage. We report that a damage-responsive checkpoint exists, but has some unusual features.

microbiology↗

bioRxiv2024

Plastid translocon recycling in dinoflagellates demonstrates the portability of complex plastids between hosts

The plastids of photosynthetic organisms on land are predominantly primary plastids derived from an ancient endosymbiosis of a cyanobacterium. Conversely, marine photosynthetic diversity is dominated by plastids gained by subsequent endosymbioses of photosynthetic eukaryotes, so-called complex plastids. The plastids of major eukaryotic lineages including cryptophytes, haptophytes, stramenopiles, dinoflagellates and apicomplexans, were originally all posited to derive from a single secondary endosymbiosis of a red alga--the chromalveloate hypothesis 1. Subsequent phylogenetic resolution of eukaryotes indicated that separate events of plastid acquisition must have occurred to account for this distribution of plastids 2,3. The number of such events, however, and the donor organisms for the new plastid endosymbioses are still not resolved. A perceived bottleneck of endosymbiotic plastid gain is the development of protein targeting from the hosts into new plastids, and this supposition has often driven hypotheses towards minimising the number of plastid-gain events to explain plastid distribution in eukaryotes. But how plastid protein-targeting is established for new endosymbionts is often unclear, which makes it difficult to assess the likelihood of plastid transfers between lineages. Here we show that Kareniaceae dinoflagellates, that possess complex plastids known to be derived from haptophytes, acquired all the necessary protein import machinery from these haptophytes. Furthermore, cryo-electron tomography revealed that no additional membranes were added to the Kareniaceae complex plastid during serial endosymbiosis, suggesting that the haptophyte-derived import processes were sufficient. Our analyses suggests that complex red plastids are preadapted for horizontal transmission, potentially explaining their widespread distribution in aquatic algal diversity.

evolutionary biology↗

bioRxiv2024

Semi-supervised Bayesian integration of multiple spatial proteomics datasets

The subcellular localisation of proteins is a key determinant of their function. High-throughput analyses of these localisations can be performed using mass spectrometry-based spatial proteomics, which enables us to examine the localisation and relocalisation of proteins. Furthermore, complementary data sources can provide additional sources of functional or localisation information. Examples include protein annotations and other high-throughput omic assays. Integrating these modalities can provide new insights as well as additional confidence in results, but existing approaches for integrative analyses of spatial proteomics datasets are limited in the types of data they can integrate and do not quantify uncertainty. Here we propose a semi-supervised Bayesian approach to integrate spatial proteomics datasets with other data sources, to improve the inference of protein sub-cellular localisation. We demonstrate our approach outperforms other transfer-learning methods and has greater flexibility in the data it can model. To demonstrate the flexibility of our approach, we apply our method to integrate spatial proteomics data generated for the parasite Toxoplasma gondii with time-course gene expression data generated over its cell cycle. Our findings suggest that proteins linked to invasion organelles are associated with expression programs that peak at the end of the first cell-cycle. Furthermore, this integrative analysis divides the dense granule proteins into heterogeneous populations suggestive of potentially different functions. Our method is disseminated via the mdir R package available on the lead authors Github. Author summaryProteins are located in subcellular environments to ensure that they are near their interaction partners and occur in the correct biochemical environment to function. Where a protein is located can be determined from a number of data sources. To integrate diverse datasets together we develop an integrative Bayesian model to combine the information from several datasets in a principled manner. We learn how similar the dataset are as part of the modelling process and demonstrate the benefits of integrating mass-spectrometry based spatial proteomics data with timecourse gene-expression datasets.

systems biology↗

bioRxiv2023

Apical annuli are specialised sites of post-invasion secretion of dense granules in Toxoplasma

Apicomplexans are ubiquitous intracellular parasites of animals. These parasites use a programmed sequence of secretory events to find, invade, and then reengineer their host cells to enable parasite growth and proliferation. The secretory organelles micronemes and rhoptries mediate the first steps of invasion. Both secrete their contents through the apical complex which provides an apical opening in the parasites elaborate inner membrane complex (IMC) -- an extensive subpellicular system of flattened membrane cisternae and proteinaceous meshwork that otherwise limits access of the cytoplasm to the plasma membrane for material exchange with the cell exterior. After invasion, a second secretion programme drives host cell remodelling and occurs from dense granules. The site(s) of dense granule exocytosis, however, has been unknown. In Toxoplasma gondii, small subapical annular structures that are embedded in the IMC have been observed, but the role or significance of these apical annuli to plasma membrane function has also been unknown. Here, we determined that integral membrane proteins of the plasma membrane occur specifically at these apical annular sites, that these proteins include SNARE proteins, and that the apical annuli are sites of vesicle fusion and exocytosis. Specifically, we show that dense granules require these structures for the secretion of their cargo proteins. When secretion is perturbed at the apical annuli, parasite growth is strongly impaired. The apical annuli, therefore, represent a second type of IMC-embedded structure to the apical complex that is specialised for protein secretion, and reveal that in Toxoplasma there is a physical separation of the processes of pre- and post-invasion secretion that mediate host-parasite interactions.

cell biology↗

bioRxiv2023

Early infection response of the first trimester human placenta at single-cell scale

Placental infections are a major worldwide burden, particularly in developing countries. The placenta is a transient tissue located at the interface between the mother and the fetus. Some pathogens can access the placental barrier resulting in pathological transmission from mother to fetus, which may have a profound impact on the health of the developing fetus. Limited tissue accessibility, critical differences between humans and mice, and, until recently, lack of proper in vitro models, have hampered our understanding of the early placental response to pathogens. Here we use single-cell transcriptomics to describe the placental primary defence mechanisms against three pathogens that are known to cause fetal and maternal complications during pregnancy - Plasmodium falciparum, Listeria monocytogenes and Toxoplasma gondii. We optimise ex vivo placental explants of the first-trimester human placenta and show that trophoblasts (the epithelial-like cells of the placenta), and Hofbauer cells (placental macrophages) orchestrate a coordinated inflammatory response after 24 hours of infection. We show that hormone biosynthesis and transport are downregulated in the trophoblasts, suggesting that protective responses are promoted at the expense of decreasing other critical functions of the placenta, such as the endocrine production and the nourishment of the fetus. In addition, we pinpoint pathogen-specific effects in some placental lineages, including a strong mitochondrial alteration in the Hofbauer cells in response to T. gondii. Finally, we identify adaptive strategies and validate nutrient acquisition employed by the P. falciparum during placental malaria infection. This study provides the first detailed cellular map of the first-trimester placenta upon infection and describes the early events that may lead to fetal and placental disorders if left unchecked.

genomics↗

bioRxiv2022

Stable and ancient endocytic structures navigate the complex pellicle of apicomplexan parasites

Apicomplexan parasites have an immense impact on humanity, but their basic cellular processes are often poorly understood. The sites of endocytosis, the conservation of this process with other eukaryotes, and its functions across Apicomplexa are major unanswered questions. Yet endocytosis in Plasmodium is implicated in antimalarial drug failure. Using the apicomplexan model Toxoplasma, we identified the molecular composition and behavior of unusual, fixed endocytic structures. Here, stable complexes of endocytic proteins differ markedly from the dynamic assembly/disassembly of these machineries in other eukaryotes. Moreover, conserved molecular adaptation of this structure is seen in Apicomplexa, including the kelch-domain protein K13 central to malarial drug-resistance. We determine that an essential function of endocytosis in Toxoplasma is plasma membrane homeostasis, rather than parasite nutrition, and that these specialized endocytic structures originated early in infrakingdom Alveolata, likely in response to the complex cell pellicle that defines this medically and ecologically important ancient eukaryotic lineage.

cell biology↗

bioRxiv2022

Mitochondrial genomes in Perkinsus decode conserved frameshifts in all genes

Mitochondrial genomes of apicomplexans, dino-flagellates and chrompodellids, that collectively make up the Myzozoa, are uncommonly reduced in coding capacity and display divergent gene configuration and expression mechanisms. They encode only three proteins -- COB, COX1, COX3 -- contain rRNAs fragmented to [~]100-200 base pair elements, and employ extensive recombination, RNA trans-splicing, and RNA-editing for genome maintenance and expression. The early-diverging Perkinsozoa is the final major myzozoan lineage whose mitochondrial genomes remain poorly characterized. Previous reports of Perkinsus cox1 and cob partial gene sequences have indicated independent acquisition of non-canonical features, namely the occurrence of multiple frameshifts in both genes. To determine ancestral myzozoan mitochondrial genome features, as well as any novel ones in Perkinsozoa, we sequenced and assembled four Perkinsus species mitochondrial genomes. These data show a simple ancestral genome with the common reduced coding capacity, but one already prone to rearrangement. Moreover, we identified 75 frameshifts across the four species that are present in all genes, that are highly conserved in gene location, and that occur as four distinct types. A decoding mechanism apparently employs unused codons at the frameshift sites that advance translation either +1 or +2 frames to the next used codon. The locations of the frameshifts are seemingly positioned to regulate protein folding of the nascent protein as it emerges from the ribosome. COX3 is distinct in containing only one frameshift and showing strong selection against residues that are otherwise frequently encoded at the frameshift positions in COX3 and COB. All genes also lack cysteine codons implying a further constraint on these genomes with reduction to only 19 different amino acids. Furthermore, mitochondrion-encoded rRNA fragment complements are incomplete in Perkinsus spp. but some are found in the nuclear DNA, suggesting these may be imported into the organelle as for tRNAs. Perkinsus demonstrates additional remarkable trajectories of organelle genome evolution including pervasive integration of frameshift translation into genome expression.

molecular biology↗

bioRxiv2021

Development of the myzozoan aquatic parasite Perkinsus marinus as a versatile experimental genetic model organism

The phylum Perkinsozoa is an aquatic parasite lineage that has devastating effects on commercial and natural mollusc populations, and also comprises parasites of algae, fish and amphibians. They are related to, and share much of their biology with, dinoflagellates and apicomplexans and thus offer excellent genetic models for both parasitological and evolutionary studies. Genetic transformation has been previously achieved for select Perkinsus spp. but with few tools for transgene expression and only limited selection efficacy. We thus sought to expand the power of experimental genetic tools for Perkinsus marinus -- the principal perkinsozoan model to date. We constructed a modular plasmid assembly system that enables expression of multiple genes simultaneously. We developed an efficient selection system for three drugs, puromycin, bleomycin and blasticidin, that achieves transformed cell populations in as little as three weeks. We developed and quantified eleven new promoters of variable expression strength. Furthermore, we identified that genomic integration of transgenes is predominantly via non-homologous recombination and often involves transgene fragmentation including deletion of some introduced elements. To counter these dynamic processes, we show that bi-cistronic transcripts using the viral 2A peptides can couple selection systems to the maintenance of the expression of a transgene of interest. Collectively, these new tools and insights provide new capacity to efficiently genetically modify and study Perkinsus as an aquatic parasite and evolutionary model.

genetics↗

bioRxiv2021

Repurposing of Synaptonemal Complex Proteins for Kinetochores in Kinetoplastida

Chromosome segregation in eukaryotes is driven by a macromolecular protein complex called the kinetochore that connects centromeric DNA to microtubules of the spindle apparatus. Kinetochores in well-studied model eukaryotes consist of a core set of proteins that are broadly conserved among distant eukaryotic phyla. In contrast, unicellular flagellates of the class Kinetoplastida have a unique set of kinetochore components. The evolutionary origin and history of these kinetochores remains unknown. Here, we report evidence of homology between three kinetoplastid kinetochore proteins KKT16-18 and axial element components of the synaptonemal complex, such as the SYCP2:SYCP3 multimers found in vertebrates. The synaptonemal complex is a zipper-like structure that assembles between homologous chromosomes during meiosis to promote recombination. Using a sensitive homology detection protocol, we identify divergent orthologues of SYCP2:SYCP3 in most eukaryotic supergroups including other experimentally established axial element components, such as Red1 and Rec10 in budding and fission yeast, and the ASY3:ASY4 multimers in land plants. These searches also identify KKT16-18 as part of this rapidly evolving protein family. The widespread presence of the SYCP2-3 gene family in extant eukaryotes suggests that the synaptonemal complex was likely present in the last eukaryotic common ancestor. We found at least twelve independent duplications of the SYCP2-3 gene family throughout the eukaryotic tree of life, providing opportunities for new functional complexes to arise, including KKT16-18 in Trypanosoma brucei. We propose that kinetoplastids evolved their unique kinetochore system by repurposing meiotic components of the chromosome synapsis and homologous recombination machinery that were already present in early eukaryotes.

cell biology↗

bioRxiv2021

A prioritized and validated resource of mitochondrial proteins in Plasmodium identifies leads to unique biology

Plasmodium species have a single mitochondrion that is essential for their survival and has been successfully targeted by anti-malarial drugs. Most mitochondrial proteins are imported into this organelle and our picture of the Plasmodium mitochondrial proteome remains incomplete. Many data sources contain information about mitochondrial localization, including proteome and gene expression profiles, orthology to mitochondrial proteins from other species, co-evolutionary relationships, and amino acid sequences, each with different coverage and reliability. To obtain a comprehensive, prioritized list of Plasmodium falciparum mitochondrial proteins, we rigorously analyzed and integrated eight datasets using Bayesian statistics into a predictive score per protein for mitochondrial localization. At a corrected false discovery rate of 25%, we identified 445 proteins with a sensitivity of 87% and a specificity of 97%. They include proteins that have not been identified as mitochondrial in other eukaryotes but have characterized homologs in bacteria that are involved in metabolism or translation. Mitochondrial localization of seven Plasmodium berghei orthologs was confirmed by epitope labeling and co-localization with a mitochondrial marker protein. One of these belongs to a newly identified apicomplexan mitochondrial protein family that in P. falciparum has four members. With the experimentally validated mitochondrial proteins and the complete ranked P. falciparum proteome, which we have named PlasmoMitoCarta, we present a resource to study unique proteins of Plasmodium mitochondria.

bioinformatics↗

bioRxiv2020

Conservation of the Toxoplasma conoid proteome in Plasmodium reveals a cryptic conoid feature that differentiates between blood- and vector-stage zoite

The apical complex is the instrument of invasion used by apicomplexan parasites, and the conoid is a conspicuous feature of this apparatus found throughout this phylum. The conoid, however, is believed to be heavily reduced or missing from Plasmodium species and other members of the class Aconoidasida. Relatively few conoid proteins have previously been identified, making it difficult to address how conserved this feature is throughout the phylum, and whether it is genuinely missing from some major groups. Moreover, parasites such as Plasmodium species cycle through three invasive forms and there is the possibility of differential presence of the conoid between these stages. We have applied spatial proteomics and high-resolution microscopy to develop a more complete molecular inventory and understanding of the organisation of conoid-associated proteins in the model apicomplexan Toxoplasma gondii. These data revealed molecular conservation of all conoid substructures throughout Apicomplexa, including Plasmodium, and even in allied Myzozoa such as Chromera and dinoflagellates. We reporter-tagged and observed the expression and location of several conoid complex proteins in the malaria model P. berghei and revealed equivalent structures in all of its zoite forms, as well as evidence of molecular differentiation between blood-stage merozoites and the ookinetes and sporozoites of the mosquito vector. Collectively we show that the conoid is a conserved apicomplexan element at the heart of the invasion mechanisms of these highly successful and often devastating parasites.

cell biology↗

bioRxiv2020

A subcellular atlas of Toxoplasma reveals the functional context of the proteome

Apicomplexan parasites cause major human disease and food insecurity. They owe their considerable success to novel, highly specialized cell compartments and structures. These adaptations drive their recognition and non-destructive penetration of hosts cells and the elaborate reengineering of these cells to promote growth, dissemination, and the countering of host defenses. The evolution of unique apicomplexan cellular compartments is concomitant with vast proteomic novelty that defines these new cell organizations and their functions. Consequently, half of apicomplexan proteins are unique and uncharacterized, and these cells are, therefore, very poorly understood. Here, we determine the steady-state subcellular location of thousands of proteins simultaneously within the globally prevalent apicomplexan parasite Toxoplasma gondii. This provides unprecedented comprehensive molecular definition to these cells and their novel compartments, and these data reveal the spatial organizations of protein expression and function, adaptation to hosts, and the underlying evolutionary trajectories of these pathogens.

cell biology↗

bioRxiv2019

Systematic analysis of Plasmodium myosins reveals differential expression, localization and function in invasive and proliferative parasite stages

The myosin superfamily comprises of actin-dependent eukaryotic molecular motors important in a variety of cellular functions. Although well studied in many systems, knowledge of their functions in Plasmodium, the causative agent of malaria, is restricted. Previously, six myosins were identified in this genus, including three Class XIV myosins found only in Apicomplexa and some Ciliates. The well characterised MyoA, is a class XIV myosin essential for gliding motility and invasion. Here, we characterize all other Plasmodium myosins throughout the parasite life cycle and show that they have very diverse patterns of expression and cellular location. MyoB and MyoE, the other two Class XIV myosins, are expressed in all invasive stages, with apical and basal locations, respectively. Gene deletion revealed that MyoE is involved in sporozoite motility, MyoF and MyoK are likely essential in the asexual blood stages, and MyoJ and MyoB are not essential. Both MyoB and its essential light chain (MCL-B) are localised at the apical end of ookinetes but expressed at completely different time points. This work provides a better understanding of the role of actomyosin motors in Apicomplexan parasites, particularly in the motile and invasive stages of Plasmodium during sexual and asexual development within the mosquito.

cell biology↗

bioRxiv2018

Genetic transformation of the dinoflagellate chloroplast

Coral reefs are some of the most important and ecologically diverse marine environments. At the base of the reef ecosystem are dinoflagellate algae, living in symbiosis with coral. Efforts to understand the relationship between alga and coral have been greatly hampered by the lack of an appropriate dinoflagellate genetic transformation technology. By making use of the plasmid-like fragmented chloroplast genome, we have introduced novel genetic material into the dinoflagellate chloroplast genome. We have shown that the introduced genes are expressed and confer the expected phenotypes. Genetically modified cultures have been grown for five months with subculturing, maintaining the introduced genes and phenotypes. This indicates that cells continue to divide after transformation and that the transformation is stable.

genetics↗

bioRxiv2018

A Pentatricopeptide Repeat Protein in the Plasmodium apicoplast is essential and shows sequence-specific RNA binding

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. Little is known about the mechanism of post-transcriptional processing. In plant chloroplasts, post-transcriptional RNA processing is controlled by multiple pentatricopeptide repeat (PPR) proteins. Here, we present the biochemical characterisation of the single apicoplast-targeted PPR protein. Apicoplast PPR1 is essential, and binds specific RNA sequences corresponding with previously characterized RNA processing sites. We identify the specific binding motif of PPR1. In RNAse protection assays, PPR1 shields apicoplast transcripts from ribonuclease degradation. Our results show that apicoplast RNA processing is under the control of a single protein, thus presenting an Achilles heel for the development of new anti-malarial drugs.

microbiology↗