Competitive resource allocation drives asynchronous and rapid nuclear multiplication in the malaria parasite

The unicellular malaria parasite Plasmodium falciparum proliferates within the red blood cells of its human host, where it generates approximately 20 new parasites within an infection cycle of two days. Proliferation proceeds by nuclear divisions in a shared cytoplasm, followed by cellularization. In stark contrast to the highly synchronized nuclear division cycles in many eukaryotes, Plasmodium nuclear cycles desynchronize rapidly. Here, we elucidate the mechanism of desynchronization and study its impact on parasite fitness by combining live-cell imaging of DNA replication with biophysical modeling. We find that the standard model of independent nuclear cycles with transgenerational inheritance cannot account for the experimental data, and therefore desynchronization requires nuclear coupling. Competition for a limiting pool of a replication resource explains the data, provided that the resource is allocated sequentially to individual nuclei. Sequential allocation can be achieved by stable but reversible loading of a replication component to DNA, for example proliferating cell nuclear antigen (PCNA). Remarkably, the resultant asynchronous nuclear cycles accelerate parasite proliferation by minimizing idling times of resources. Indeed, we predict theoretically that this mechanism maximizes overall proliferation rate with limited resource availability. Thus, our findings identify nuclear cycle asynchrony as a resource-efficient means to achieve rapid proliferation.