Plasmodium actin-like proteins are essential for DNA segregation during male gametogenesis and malaria transmission.

Protozoan parasites of the genus Plasmodium cause malaria and involve infection of multiple hosts and cell types during the life cycle. Producing sexually fit gametocytes is essential for transmitting the Plasmodium parasite into an anopheline mosquito vector. After the uptake of malaria parasites, male gametocytes undergo three rounds of DNA replication to produce eight nucleated flagellar gametes. Here, we report that the actin-like proteins Alp5a and Alp5b are involved in DNA segregation during male gametogenesis. The Plasmodium-specific Alp5a and Alp5b can be superimposed on human Arp2 and Arp3, localize to the nucleus, and interact with each other. Alp5a and Alp5b are individually dispensable for the development of P. berghei blood stages, but are simultaneously indispensable for parasite viability. Consistent with genetic studies, the inhibitory activity of the Arp2/3 complex inhibitor in Plasmodium supports an essential role for this complex during the blood stage. Deletion of Alp5a or Alp5b had no impact on actin nucleation, parasite growth, or gametocytemia during the blood stage. The knockout parasites were able to invade the mosquito midgut and form oocysts; however, these oocysts were significantly smaller in size and failed to mature, ultimately leading to their death. Genetic crosses revealed defects in male gamete integrity. We found that the reduced oocyst development was due to impaired DNA segregation during male gametogenesis. Our study provides molecular insights into the fundamental requirements of the Alps in Plasmodium, which are essential for malaria transmission.