Significance: Rhodnius prolixus is a major vector of Chagas disease, an illness caused by Trypanosoma cruzi which affects approximately 7 million people worldwide. This report describes the first genome sequence of a nondipteran insect vector of an important human parasitic disease. This insect has a gene repertoire substantially distinct from dipteran disease vectors, including immune signaling pathways that display major departures from the canonical network. Large gene expansions related to chemoreception, feeding, and digestion have facilitated triatomine adaptation to a blood-feeding lifestyle. This study provides information about the physiology and evolution of an important disease vector that will boost understanding of transmission of a life-threatening parasite and may lead to the development of innovative control methods.

The bloodsucking hemipteran Rhodnius prolixus is a vector of Chagas' disease, which affects 7–8 million people today in Latin America. In contrast to other hematophagous insects, the triatomine gut is compartmentalized into three segments that perform different functions during blood digestion. Here we report analysis of transcriptomes for each of the segments using pyrosequencing technology. Comparison of transcript frequency in digestive libraries with a whole-body library was used to evaluate expression levels. All classes of digestive enzymes were highly expressed, with a predominance of cysteine and aspartic proteinases, the latter showing a significant expansion through gene duplication. Although no protein digestion is known to occur in the anterior midgut (AM), protease transcripts were found, suggesting secretion as pro-enzymes, being possibly activated in the posterior midgut (PM). As expected, genes related to cytoskeleton, protein synthesis apparatus, protein traffic, and secretion were abundantly transcribed. Despite the absence of a chitinous peritrophic membrane in hemipterans - which have instead a lipidic perimicrovillar membrane lining over midgut epithelia - several gut-specific peritrophin transcripts were found, suggesting that these proteins perform functions other than being a structural component of the peritrophic membrane. Among immunity-related transcripts, while lysozymes and lectins were the most highly expressed, several genes belonging to the Toll pathway - found at low levels in the gut of most insects - were identified, contrasting with a low abundance of transcripts from IMD and STAT pathways. Analysis of transcripts related to lipid metabolism indicates that lipids play multiple roles, being a major energy source, a substrate for perimicrovillar membrane formation, and a source for hydrocarbons possibly to produce the wax layer of the hindgut. Transcripts related to amino acid metabolism showed an unanticipated priority for degradation of tyrosine, phenylalanine, and tryptophan. Analysis of transcripts related to signaling pathways suggested a role for MAP kinases, GTPases, and LKBP1/AMP kinases related to control of cell shape and polarity, possibly in connection with regulation of cell survival, response of pathogens and nutrients. Together, our findings present a new view of the triatomine digestive apparatus and will help us understand trypanosome interaction and allow insights into hemipteran metabolic adaptations to a blood-based diet. The bloodsucking bug Rhodnius prolixus is a vector of Chagas' disease, which affects 7–8 million people in Latin America. In contrast to other insects, the digestive tract of Rhodnius has three segments that perform different functions during blood digestion. Here we report analysis of transcriptomes for each of these segments using pyrosequencing technology amounting to several million sequences. Comparison of transcript frequency in digestive libraries with a whole-body library was used to evaluate expression levels, leading to the discovery of several families of enzymes associated with the digestion of proteins, carbohydrates, and lipids, as well as proteins involved in immunity, signal transduction, amino-acid metabolism, and detoxification. Together, our findings present a new view of the triatomine digestive apparatus and will help us understand the mechanism of blood digestion by Rhodnius and its interaction with the agent of Chagas' disease, Trypanosoma cruzi, a parasite that grows within the insect's digestive system.

Rhodnius prolixus is a blood-feeding insect that can transmit Trypanosoma cruzi and Trypanosoma rangeli to vertebrate hosts. Recently, genomic resources for invertebrate vectors of human pathogens have increased significantly, and R. prolixus has been one of the main species studied among the triatomines. However, the paucity of information on many of the fundamental molecular aspects of this species limits the use of the available genomic information. The present study aimed to facilitate gene expression studies by identifying the most suitable reference genes for the normalization of mRNA expression data from qPCR.