In silicoidentification and expression analyses ofDefensingenes in the mealworm beetleTenebrio molitor

Abstract

Defensins are a major family of antimicrobial peptides that serve as the innate immune defense of both vertebrates and invertebrates. Due to their antimicrobial, chemotactic, and regulatory activities, Defensins have been exploited for their therapeutic potential. Insect Defensins are cysteine-rich and contain an N-terminal loop, alpha-helix, and antiparallel beta-sheet, forming a "cysteine-stabilized alpha beta (CS alpha beta)" or "loop-helix-sheet" structure. In this study, we identified the full-length open reading frame (ORF) sequences ofDefensin(TmDef) andDefensin-like(TmDef-like) genes from the mealworm beetleTenebrio molitorusingin silicomethods.TmDefandTmDef-likegenes encode the peptides of 72 and 71 amino acid residues, respectively.TmDefensin is comprised of a Defensin domain and theTmDefensin-like is comprised of a signal peptide of 21 amino acid residues. Phylogenetic analysis revealed close similarities ofTmDefensin with the Defensin ofAcalolepta luxuriosaof the longhorn beetle family. The expression ofTmDefmRNA was found to be greater than that ofTmDef-likemRNA and was mostly expressed in the pupal and adult stages. Tissue distribution showed high expression ofTmDef-likemRNA in larval hemocytes, gut, integument, and fat body, while in adults, the expression was high in gut and hemocytes. Following bacterial and fungal stimulationin vivo,TmDefwas upregulated at 24 h post-infection in whole body, fat body, and hemocytes of the larvae. EvenTmDef-likemRNA was upregulated in the gut and hemocytes at 12 and 9 h post-infection respectively. These results suggest thatTmDefandTmDef-likegenes play important roles in protectingT. molitorfrom microbial contact.