Expression patterns and functional exploration of CO 2 receptor genes in Anopheles sinensis (Diptera: Culicidae)

Abstract Carbon dioxide (CO₂), as a chemical signal, plays an essential role for the host-seeking of mosquitoes, and CO₂ receptor genes (CRGs) have been proposed to be responsible of the host-seeking behavior in some insects. However, the expression patterns of CRGs have yet to explore, and the function in host-seeking behavior response has only limitedly understood. In this study, we investigated the characteristics, phylogenetics, expression patterns, and function of three CRGs in An. sinensis. The CRGs from six mosquito and four other dipteran species were identified and phylogenetically classified in three groups, and all mosquitoes have three CRGs that are classified into GR1, GR2 and GR3 with GR2 being specific for mosquitoes, and other dipteran insects have only two CRGs that are classified into GR1 and GR3. All three CRGs were specifically expressed in maxillary palps in An. sinensis; however, only AsinGR22 and AsinGR24 were significantly up-regulated in females than in males, and all three CRGs were significantly down-regulated post blood feeding. Functional analysis using RNAi revealed that AsinGR22 and AsinGR24 mediate the capacity for CO₂ detection of female adults, but AsinGR23 might enhance the capacity as a regulatory factor rather than a functional gene. All these three genes demonstrated no influence to blood feeding behavior. This is the first comprehensive study on CRGs in An. sinensis. This study revealed the function of CRGs in CO₂ detection and blood-sucking behavior, and provided a comprehensive information frame for further research on function and application of CRGs in mosquitoes.