The Silencing of a 14-3-3 epsilon Homolog in Tenebrio molitor Leads to Increased Antimicrobial Activity in Hemocyte and Reduces Larval Survivability

Abstract

The 14-3-3 family of phosphorylated serine-binding proteins acts as signaling molecules in biological processes such as metabolism, division, differentiation, autophagy, and apoptosis. Herein, we report the requirement of 14-3-3 epsilon isoform from Tenebrio molitor (Tm14-3-3 epsilon) in the hemocyte antimicrobial activity. The Tm14-3-3 epsilon transcript is 771 nucleotides in length and encodes a polypeptide of 256 amino acid residues. The protein has the typical 14-3-3 domain, the nuclear export signal (NES) sequence, and the peptide binding residues. The Tm14-3-3 epsilon transcript shows a significant three-fold expression in the hemocyte of T. molitor larvae when infected with Escherichia coli Tm14-3-3 epsilon silenced larvae show significantly lower survival rates when infected with E. coli. Under Tm14-3-3 epsilon silenced condition, a strong antimicrobial activity is elicited in the hemocyte of the host inoculated with E. coli. This suggests impaired secretion of antimicrobial peptides (AMP) into the hemolymph. Furthermore, a reduction in AMP secretion under Tm14-3-3 epsilon silenced condition would be responsible for loss in the capacity to kill bacteria and might explain the reduced survivability of the larvae upon E. coli challenge. This shows that Tm14-3-3 epsilon is required to maintain innate immunity in T. molitor by enabling antimicrobial secretion into the hemolymph and explains the functional specialization of the isoform.