Reverse genetics demonstrate the role of mucosal C-type lectins in food particle selection in the oyster Crassostrea virginica

Abstract

Prey selection governs species interactions and regulates physiological energetics of individuals and populations. Suspension-feeding bivalves represent key species in coastal and estuarine systems for their ecological and economic value. These animals are able to sort and selectively ingest nutritious microalgae from dilute and composite mixtures of particulate matter. This aptitude was suggested to be mediated by interactions between carbohydrates associated with the surface of microalgae and C-type lectins present in mucus covering the feeding organs although a direct, unequivocal, role of lectins in food sorting in bivalves remains elusive. This study was designed to identify and characterize mucosal C-type lectins from oysters and manipulate the expression of these proteins in order to obtain decisive information regarding their involvement in food choice. Thus, 2 mucosal C-type lectins (CvML3912 and CvML3914) were identified based on transcriptomic and proteomic information. Transcripts of these lectins were detected in the feeding organs and their expression was upregulated following starvation. Recombinant lectin (rCvML3912) competitively inhibited the binding of commercial mannose/glucose-specific lectins to microalgae. Short DsiRNA targeting these two lectins were designed and used to evaluate the effect of gene silencing on food particle sorting. As a result, the abundance of the two cognate transcripts significantly decreased and food sorting ability was significantly reduced among silenced oysters as compared to control animals. Overall, these findings propose a novel concept establishing the role of carbohydrate-protein interactions to provide an efficient food particle sorting, and establish a new dimension for the role of evolutionarily-conserved mannose/glucose-binding proteins in the metazoan.