In silico identification, characterization and expression analysis of attacin gene family in response to bacterial and fungal pathogens in Tenebrio molitor

Antimicrobial peptides are effector molecules induced after microbial challenges. These form important components of innate host defense against the pathogens by exhibiting wide-spectrum antimicrobial activities. In this study, we identified three attacin-like genes from Tenebrio molitor RNASeq database using Tribolium castaneum attacin gene family as query. The T. molitor attacin gene family was annotated as TmAttacin-1a [comprising of 154 amino acids (aa)], TmAttacin-1b (150 aa) and TmAttacin-2 (164 aa), respectively. Temporal expression analysis shows that the TmAttacin-1a and -1b mRNAs are highly expressed in late larval stages, followed by a general decline in the pre-pupal stages. The mRNA level shows a decline during metamorphosis, and gets slightly overexpressed in pupal-adult transition stages. On the other hand, TmAttacin-2 is mainly overexpressed at 1-day old pupal stage. Spatial expression analysis indicates that TmAttacin-1a, -1b, and -2 mRNAs are primarily expressed in gut and fat body, but not in hemocytes and Malpighian tubules in T. molitor larvae. Interestingly, TmAttacin-1b shows more than 20-fold expression in the ovary, whereas TmAttacin-1a and -2 show similar expression patterns in gut, fat body, hemocyte, ovary, and testis in T. molitor adults. Induction pattern analysis demonstrates that the intracellular Gram-positive bacteria, L. monocytogenes elicited the strongest response by inducing similar to 1,000-fold expression of TmAttacin-1a mRNA. The highest level of TmAttacin-1b mRNA (similar to 350-fold) was induced by Gram-negative bacteria, E. coli. However, the TmAttacin-2 transcripts were not induced by microbial challenges. These results indicate that TmAttacin-1a and -1b may be required for antimicrobial defenses in T. molitor.