Sialotranscriptomics of Rhipicephalus appendiculatus Male and Female Ticks

Ticks are blood-feeding ectoparasites that vector a variety of human and veterinary diseases worldwide. By injecting secretory proteins into the host they create a stable feeding site to feed unnoticed for extended periods of time. Tick secretory proteins modulate the host’s haemostasis, inflammation and immune responses and are attractive vaccine candidates. Many of these proteins are uncharacterised due to limited sequence availability for ticks and other arthropods, but recent advances in next generation sequencing technologies have made sequencing of non-model organisms such as arthropods more affordable. To this end, we sequenced adult male and female Rhipicephalus appendiculatus salivary glands during feeding. Illumina MiSeq and HiSeq 2000 sequencing instruments were used to generate nearly 430 million paired end reads. A sialotranscriptome of 21 410 transcripts was de novo assembled from the trimmed reads and translated into 12 761 non-redundant proteins. Transcripts annotated as secretory proteins represented the smallest class of proteins in the transcriptome (17%) but accounted for most of the expression (63%). Of the secretory protein class expression, transcripts of the Glycine rich superfamily contributed 66% and transcripts of the Lipocalin family, 12%. Gender-skewed transcript expression was observed for a number of secretory protein families. Differential expression analysis identified 2346 male and 1758 female up regulated transcripts, suggestive of varying blood-feeding mechanisms employed between male and female ticks. This sialotranscriptome greatly improves on the sequence information available for R. appendiculatus, will improve our understanding of tick feeding biology and will be a valuable resource for future vaccine candidate selection.