Dominant negative mutant of Plasmodium Rad51 causes reduced parasite burden in host by abrogating DNA double-strand break repair.

Malaria parasites survive through repairing a plethora of DNA double-stranded breaks (DSBs) experienced during their asexual growth. In Plasmodium Rad51 mediated homologous recombination (HR) mechanism and homology-independent alternative end-joining mechanism have been identified. Here we address whether loss of HR activity can be compensated by other DSB repair mechanisms. Creating a transgenic Plasmodium line defective in HR function, we demonstrate that HR is the most important DSB repair pathway in malarial parasite. Using mouse malaria model we have characterized the dominant negative effect of PfRad51(K143R) mutant on Plasmodium DSB repair and host-parasite interaction. Our work illustrates that Plasmodium berghei harbouring the mutant protein (PfRad51(K143R)) failed to repair DSBs as evidenced by hypersensitivity to DNA-damaging agent. Mice infected with mutant parasites lived significantly longer with markedly reduced parasite burden. To better understand the effect of mutant PfRad51(K143R) on HR, we used yeast as a surrogate model and established that the presence of PfRad51(K143R) completely inhibited DNA repair, gene conversion and gene targeting. Biochemical experiment confirmed that very low level of mutant protein was sufficient for complete disruption of wild-type PfRad51 activity. Hence our work provides evidence that HR pathway of Plasmodium could be efficiently targeted to curb malaria.