Complex nutrient channel phenotypes despite Mendelian inheritance in a Plasmodium falciparum genetic cross

• Published in: PLoS pathogens Vol. 16; no. 2; p. e1008363
• Main Authors: Gupta, Ankit, Bokhari, Abdullah A B, Pillai, Ajay D, Crater, Anna K, Gezelle, Jeanine, Saggu, Gagandeep, Nasamu, Armiyaw S, Ganesan, Suresh M, Niles, Jacquin C, Desai, Sanjay A
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 18.02.2020; Public Library of Science (PLoS)
• Subjects: Bioengineering; Biological Transport; Biology and Life Sciences; Blood plasma; Cell Adhesion Molecules - genetics; Cell Adhesion Molecules - metabolism; Chromosomes; Crosses, Genetic; Epigenetic inheritance; Epigenetics; Erythrocytes; Erythrocytes - metabolism; Essential nutrients; Genes; Genetic aspects; Genetic research; Genetics; Genomes; Genotype & phenotype; Heredity; Infectious diseases; Ion channels; Ion Channels - genetics; Ion Channels - metabolism; Laboratories; Linkage analysis; Malaria; Malaria, Falciparum - metabolism; Medicine and Health Sciences; Nutrient transport; Nutrient uptake; Nutrients; Nutrients - metabolism; Nutrition Assessment; Oligomerization; Oligomers; Parasites; Phenotype; Phenotypes; Physical Sciences; Physiological aspects; Plasmodium falciparum; Plasmodium falciparum - genetics; Plasmodium falciparum - metabolism; Propagation; Proteins; Protozoan Proteins - genetics; Protozoan Proteins - metabolism; Red blood cells; Research and Analysis Methods; Selectivity; Switching; Transport; Vaccines; Vector-borne diseases; United States > US; Maryland; Massachusetts; India
• ISSN: 1553-7374; 1553-7366; 1553-7374
• DOI: 10.1371/journal.ppat.1008363

Malaria parasites activate a broad-selectivity ion channel on their host erythrocyte membrane to obtain essential nutrients from the bloodstream. This conserved channel, known as the plasmodial surface anion channel (PSAC), has been linked to parasite clag3 genes in P. falciparum, but epigenetic switching between the two copies of this gene hinders clear understanding of how the encoded protein determines PSAC activity. Here, we used linkage analysis in a P. falciparum cross where one parent carries a single clag3 gene to overcome the effects of switching and confirm a primary role of the clag3 product with high confidence. Despite Mendelian inheritance, CLAG3 conditional knockdown revealed remarkably preserved nutrient and solute uptake. Even more surprisingly, transport remained sensitive to a CLAG3 isoform-specific inhibitor despite quantitative knockdown, indicating that low doses of the CLAG3 transgene are sufficient to confer block. We then produced a complete CLAG3 knockout line and found it exhibits an incomplete loss of transport activity, in contrast to rhoph2 and rhoph3, two PSAC-associated genes that cannot be disrupted because nutrient uptake is abolished in their absence. Although the CLAG3 knockout did not incur a fitness cost under standard nutrient-rich culture conditions, this parasite could not be propagated in a modified medium that more closely resembles human plasma. These studies implicate oligomerization of CLAG paralogs encoded by various chromosomes in channel formation. They also reveal that CLAG3 is dispensable under standard in vitro conditions but required for propagation under physiological conditions.