In vivo gene knockdown of thioredoxin reductase in the gulf coast tick (Amblyomma maculatum)

Amblyomma maculatum, the Gulf coast tick, is a competent vector of an intracellular Rickettsia parkeri, the etiological agent of a mild disease similar to Rocky Mountain spotted fever.  The biological success of ticks requires that they evade host responses, and in so doing, they respond by producing a potent salivary cocktail of immunosuppressive, antihemostatic, and anti-inflammatory peptides.  These salivary secretions facilitate blood feeding and pathogen transmission.  The antioxidant enzyme thioredoxin reductase (TrxR) was identified in the A. maculatum sialotranscriptome.  The transcriptional abundance of TrxR was highest in unfed tick tissues,   Transcriptional expression of TrxR continued throughout the bloodmeal, indicating that TrxR was also needed for continued blood feeding.  In this work, we have examined the importance of thioreodoxin reductase in tick feeding by targeting this gene for transcriptional disruption via RNA interference.  Although the TrxR transcript abundance and enzymatic activity was reduced, there was no significant reduction in engorged tick weight or oviposition.  This suggests that redundant antioxidant systems may have compensated for the loss in TrxR activity or that the reduction in protein levels was not sufficient to detect a phenotype in the gene knockdown ticks.