Plasmodium DNA ligase I is essential for parasite blood- and liver-stage development

DNA ligases are a fundamental class of enzymes required for DNA replication and repair. They catalyze the formation of phosphodiester bonds, specifically at single-strand breaks in double-stranded DNA. The nuclear genome of malaria parasites encodes a single DNA ligase that is likely involved in nuclear and organellar DNA replication and repair. DNA ligase I from Plasmodium falciparum (PfLig1) has been biochemically characterized and shown to possess nick-sealing activity. However, its localization and function in the three genome-containing compartments-the nucleus, apicoplast, and mitochondrion-of the malaria parasites remain unknown. Here, we found that Lig1 is located primarily in the nucleus in both human and rodent malaria parasites throughout the parasite life cycle. Furthermore, we detected its presence in organelles via a chromatin immunoprecipitation-PCR assay. Our attempts to disrupt Plasmodium berghei Lig1 (PbLig1) in the blood stages have failed, indicating that the gene is likely essential. Next, we used an Flp/FRT-based conditional mutagenesis system that silences gene function in sporozoites. We demonstrated that PbLig1 is essential for parasite liver-stage development. Sporozoites lacking PbLig1 invade hepatocytes but arrest growth during mid-liver-stage development. PbLig1 cKO parasites undergo limited nuclear division and present a reduced DNA content that fails to increase beyond mid-liver stage of development. These data suggest that Lig1 is an essential enzyme for parasite blood- and liver-stage development.IMPORTANCEUnlike mammalian cells that possess multiple DNA ligases, the malaria parasite's nuclear genome encodes a single DNA ligase. This single DNA ligase is likely involved in both DNA replication and DNA repair. However, the importance of parasite DNA ligase remains largely unknown. Here, we show that Plasmodium Lig1 is primarily found within the nucleus, but it also exhibits a distribution across parasite organelles. Knockout of PbLig1 in sporozoites abolishes parasite liver-stage development, preventing the formation of hepatic merozoites and ultimately blocking the transition from the liver to the blood stage of infection. More specifically, PbLig1 is essential for nuclear division during hepatic schizogony. These findings enhance our understanding of the role of DNA ligase I in malaria parasite liver-stage development.