Jangra, A. | bioRxiv Science

bioRxiv2026

A Plasmodium falciparum PX1 haplotype is associated with reduced susceptibility to artemisinin and lumefantrine

Effective control of falciparum malaria depends on the sustained efficacy of frontline antimalarial drugs, particularly artemether-lumefantrine (AL), the most widely used therapy in Africa. However, the emergence of artemisinin partial resistance and reduced lumefantrine susceptibility in eastern Africa threaten malaria control and elimination. Robust genetic markers of decreased susceptibility to lumefantrine remain elusive, and our understanding of artemisinin resistance is incomplete. We report results of a Plasmodium falciparum genetic cross between a drug-sensitive line and a Ugandan strain exhibiting reduced susceptibility to dihydroartemisinin and lumefantrine. Targeted deep sequencing of progeny pools and 460 recombinant progeny clones derived under drug pressures revealed distinct haplotypic signatures. Drug-selection experiments identified genetic polymorphisms in Plasmodium falciparum px1, encoding a phosphoinositide-binding protein, as the strongest correlates of reduced susceptibility to dihydroartemisinin and lumefantrine. The PX1 PIN haplotype (L1222P, M1701I, D1705N) recently discovered in Ugandan parasites was highly enriched following dihydroartemisinin or lumefantrine treatment of pooled mixtures of genetically diverse Ugandan clinical isolates. This haplotype was associated with reduced susceptibility to dihydroartemisinin and lumefantrine, compared to wild-type sequence, in culture-adapted Ugandan P. falciparum lines. These results confirm that PX1 mutations were selected across geographically distinct Ugandan parasite backgrounds. Long-term competitive fitness assays demonstrated that PX1 mutations confer asexual blood-stage parasites with a growth advantage, potentially explaining a rapid rise of PX1 PIN alleles over the last two decades in Uganda. Overall, our data suggest the PX1 PIN haplotype is a robust marker of reduced AL susceptibility in African P. falciparum, enabling surveillance of emerging drug resistance.

microbiology↗

bioRxiv2026

Pioneering the Formation of 2-Carboxylic Anthraquinone: CRISPR/Cas9-Mediated Functional Validation of Octaketide Synthase and Polyketide Reductase Genes in Aloe vera

Aloe vera is an authentic medical plant abundant in aromatic polyketides, including the crucial hexaketides aloenin, aloesin, and barbaloin used in pharmaceuticals yet the enzymatic basis of their biosynthesis remained incompletely understood. While it has been suggested that octaketide synthases (OKS) initiates anthraquinones biosynthesis, heterologous expression of OKS alone consistently produces shunt polyketide products, and the mechanism underlying this derailment was uncertain. To comprehend the mechanism of anthraquinone biosynthesis, we combined biochemical constitution, structural characterization and CRISPR/Cas9-mediated editing of key genes in Aloe vera. It was for the first time demonstrated that the inclusion of a PKR (polyketide reductase) redirected the reactive intermediate toward formation of 2-carboxy anthraquinone (C16H1205). The identity of reaction product was confirmed by spectroscopic analysis which additionally rendered it clear from compounds previously misannotated in the literature. Alongside, CRISPR/Cas9-based genome editing of OKS and PKR genes resulted in significant reduction (upto 2.54 fold) in aloin content in edited lines compared to the non-edited control aloe line. Together these findings endorsed the presence of tailoring enzyme ketoreductase for the efficient and appropriate formation of anthraquinones and establish a mechanistic framework for polyketide biosynthesis in aloe plants that sustain as an indigenous herb for mankind. HighlightsThis study provides direct biochemical and genetic evidence that a tailoring enzyme is required to prevent derailment of polyketide intermediates and enable correct anthraquinone formation in plants.

genomics↗