A C-Type Lectin, RfCTL27, Activates the Immune Defense in the Red Palm Weevil (A.G. Olivier, 1791) (Coleoptera: Curculionidae: Dryophthorinae) by the Recognition of Gram-Negative Bacteria.

Red palm weevil, (Olivier), is a palm tree insect pest that causes significant damage in the many countries from the Indian sub-continent and southeast Asia into date palm-growing countries of Africa, the Middle East, and the Mediterranean Basin. This study is aimed at determining the role of a C-type lectin, RfCTL27, in the immune defense of RPW larvae. RfCTL27 is a secreted protein that possesses a QPD motif, being integral for the discrimination of Gram-negative bacteria. The abundance of transcripts in the gut and fat body was significantly higher than that in other tissues. Six hours after injection of , the expression level of in the gut of RPW larvae was significantly elevated compared with other groups. At 12 h after injection of , the expression of in fat body was dramatically induced in contrast with other treatments. More interestingly, the ability of RPW larvae to clear the pathogenic bacteria in the body cavity and gut was markedly impaired by the silencing of . Additionally, the expression levels of two antimicrobial peptide genes, in the gut and in fat body of RPW larvae, were significantly decreased. Taken together, these data suggested that RfCTL27 can recognize the Gram-negative bacterium and activate the expression of antimicrobial peptides to remove the invaded bacterial pathogens. This study provides a new scientific basis for improving the control efficiency of pathogenic microorganisms against red palm weevils in production practice.