An insight into the sialome of the horse fly, Tabanus bromius

Blood feeding animals face their host's defenses against tissue injury and blood loss while attempting to feed. One adaptation to surmount these barriers involves the evolution of a salivary potion that disarms their host's inflammatory and anti-hemostatic processes. The composition of the peptide moiety of this potion, or sialome (from the Greek sialo = saliva), can be deducted in part by proper interpretation of the blood feeder' sialotranscriptome. In this work we disclose the sialome of the blood feeding adult female Tabanus bromius. Following assembly of over 75 million Illumina reads (101 nt long) 16,683 contigs were obtained from which 4078 coding sequences were extracted. From these, 320 were assigned as coding for putative secreted proteins. These 320 contigs mapped 85% of the reads. The antigen-5 proteins family was studied in detail, indicating three Tabanus specific clades with and without disintegrin domains, as well as with and without leukotriene binding domains. Defensins were also detailed; a clade of salivary tabanid peptides was found lacking the propeptide domain ending in the KR dipeptide signaling furin cleavage. Novel protein families were also disclosed. Viral transcripts were identified closely matching the Kotonkan virus capsid proteins. Full length Mariner transposases were also identified. A total of 3043 coding sequences and their protein products were deposited in Genbank. Hyperlinked excel spreadsheets containing the coding sequences and their annotation are available at http://exon.niaid.nih.gov/transcriptome/T_bromius/Tbromius-web.xlsx (hyperlinked excel spreadsheet, 11 MB) and http://exon.niaid.nih.gov/transcriptome/T_bromius/Tbromius-SA.zip (Standalone excel with all local links, 360 MB). These sequences provide for a platform from which further proteomic studies may be designed to identify salivary proteins from T. bromius that are of pharmacological interest or used as immunological markers of host exposure.