The salivary protein Saglin facilitates efficient midgut colonization of Anopheles mosquitoes by malaria parasites

Malaria is caused by the unicelullar parasite Plasmodium which is transmitted to humans through the bite of infected female Anopheles mosquitoes. To initiate sexual reproduction and to infect the midgut of the mosquito, Plasmodium gametocytes are able to recognize the intestinal environment after being ingested during blood feeding. A shift in temperature, pH change and the presence of the insect-specific compound xanthurenic acid have been shown to be important stimuli perceived by gametocytes to become activated and proceed to sexual reproduction. Here we report that the salivary protein Saglin, previously proposed to be a receptor for the recognition of salivary glands by sporozoites, facilitates Plasmodium colonization of the mosquito midgut, but does not contribute to salivary gland invasion. In mosquito mutants lacking Saglin, Plasmodium infection of Anopheles females is greatly reduced, resulting in impaired transmission of sporozoites at low infection densities. Interestingly, our results suggest that Saglin, present in mosquito saliva, must be ingested with the blood meal to affect Plasmodium development, indicating a previously unknown host-pathogen interaction. Furthermore, we were able to show that saglin deletion has no fitness cost in laboratory conditions, suggesting this gene would be an interesting target for gene drive approaches.