De novo assembly and analysis of midgut transcriptome of Haemaphysalis flava and identification of genes involved in blood digestion, feeding and defending from pathogens

Bioactive components in the midgut of ticks play a key role in tick blood digestion, feeding and pathogen transmission. The study of protein and gene targets in midgut provides opportunities to explore novel tick control strategies. Only a few nucleotide sequences are available in public databases for Haemaphysalis flava, an important disease vector for humans and animals. Knowledge of the process of blood digestion by the ticks and protein expression in the digestive tract is limited. Here, we utilize high-throughput sequencing to characterize the midgut transcriptome of fully engorged (FE, average length of 10 mm) and partially engorged (PE, average length of 5 mm) female H. flava. 6.8 GB and 8.3 GB of high-quality sequence data were obtained using Illumina sequencing technology. 54,357,490 and 66,116,050 reads were finally assembled into 76,556 unigenes with mean length of 704 bp. The transcripts involved in blood meal digestion were classified into eight large categories, including peptidase inhibitor, peptidase (serine-, metallo-, cysteine-, aspartic-peptidase), phospholipase, carbohydrate digestion/hydrolases, lipid binding, immunity-related proteins, iron/heme metabolism and secreted proteins. A total of 5508 differentially expressed genes (DEGs) were identified between FE and PE. To confirm the DEG results, ten genes involved in blood digestion, feeding and defending from pathogens, were validated using qPCR. Our results not only contribute to better understanding of the changes in midgut transcript expression during different blood feeding stages, but also provide a valuable resource for identifying targets for future tick control studies.