Knockout of the rodent malaria parasite chitinase PbCHT1 reduces infectivity to mosquitoes

During mosquito transmission, malaria ookinetes must cross a chitin-contain ing structure known as the peritrophic matrix (PM), which surrounds the inf ected blood meal in the mosquito midgut. In turn, ookinetes produce multipl e chitinase activities presumably aimed at disrupting this physical barrier to allow ookinete invasion of the midgut epithelium. Plasmodium chitinase activities are demonstrated targets for human and avian malaria transmissio n blockade with the chitinase inhibitor allosamidin, Here, we identify and characterize the first chitinase gene of a rodent malaria parasite, Plasmod ium berghei, We show that the gene, named PbCHT1, is a structural ortholog of PgCHT1 of the avian malaria parasite Plasmodium gallinaceum and a paralo g of PfCHT1 of the human malaria parasite Plasmodium falciparum, Targeted d isruption of PbCHT1 reduced parasite infectivity in Anopheles stephensi mos quitoes by up to 90%, Reductions in infectivity were also observed in ookin ete feeds-an artificial situation where midgut invasion occurs before PM fo rmation-suggesting that PbCHT1 plays a role other than PM disruption. PbCHT 1 null mutants had no residual ookinete-derived chitinase activity in vitro ; suggesting that P. berghei ookinetes express only one chitinase gene. Mor eover, PbCHT1 activity appeared insensitive to allosamidin inhibition, an o bservation that raises questions about the use of allosamidin and component s like it as potential malaria transmission-blocking drugs. Taken together, these findings suggest a fundamental divergence among rodent, avian, and h uman malaria parasite chitinases, with implications for the evolution of Pl asmodium-mosquito interactions.