AsOBP1 is required for host seeking in the malaria vector mosquito, Anopheles sinensis

Female adult anautogenous mosquitoes rely heavily on diverse chemical stimuli to locate and discriminate hosts for feeding through their olfactory system. Odorant binding proteins are believed to be the first proteins to interact with semiochemicals in the olfactory sensory system, but their functions in host seeking have not been extensively explored. Here, we used transposon-based transgenesis and CRISPR/Cas9-based genome editing to localize and functionally characterize the odorant binding protein AsOBP1 in the malaria mosquito, Anopheles sinensis, a main vector of vivax malaria in China and other Southeast Asian countries, and uncovered its roles in host-seeking behavior of female mosquitoes. AsOBP1 is specifically expressed in the cuticle and sensilla trichodea of antennae of adult mosquitoes. Although AsOBP1(-/-) mutant females alighted on and probed blood hosts, the AsOBP1 mutation severely impaired host-seeking behavior. The in vitro competition assay identified nine of 83 human odorants, among which 1-tetradecanol and heptanal enhanced the attraction of mice and human hands to An. sinensis mosquitoes. The olfactory sensitivity of AsOBP1 mutants to these two compounds was reduced. Our study reveals that AsOBP1 is required for the host seeking of An. sinensis through detecting human odor, such as 1-tetradecanol and heptanal, and provides a potential target for malaria control.