De Novo RNA-seq and Functional Annotation of Haemaphysalis longicornis.

Purpose: Haemaphysalis longicornis (Neumann) is a hematophagous tick widely distributed in northern China. It not only causes enormous economic loss to animal husbandry, but also as a vector and reservoir of various zoonotic pathogens, it spreads natural focal diseases, such as severe fever with thrombocytopenia syndrome, seriously threatening human health. Lack of transcriptomic and genomic data from H. longicornis limits the study of this important medical vector.
Methods: The engorged female H. longicornis from Gansu, China, was used for RNA extraction, de novo RNA-seq, functional annotation, and ORF prediction.
Results: As a result, 53.09 million clean reads (98.88%) with a GC content of 54.29% were obtained. A total of 65,916 Unigenes were assembled, of which 34.59% (23,330) were successfully annotated. Of these Unigenes, 22,587 (34.27%) were annotated to species by NCBI non-redundant protein (nr). Ixodes scapularis, Limulus polyphemus, Parasteatoda tepidariorum, Stegodyphus mimosarum, and Metaseiulus occidentalis were the top BLAST hit species, accounting for 47.23%, 9.58%, 4.11%, 3.50%, and 2.69%, respectively. A total of 29,182 ORFs were predicted, and 35 complete ORFs for functional genes were identified, including ORFs involved in digestion (14), stress responses (8), anticoagulation (3), reproduction (3), antimicrobial (2), drug resistance (2), movement (2), autophagy (1), and immunity (1), respectively. The Unigene ORFs encoding cathepsin and heat shock proteins were further analyzed phylogenetically.
Conclusion: De novo RNA-seq and functional annotation of H. longicornis were successfully completed for the first time, providing a molecular data resource for further research on blood-sucking, pathogen transmission mechanisms, and effective prevention and control strategies.