Characterization and Expression Analysis of Attacins, Antimicrobial Peptide-Encoding Genes, from the Desert Beetle Microdera punctipennis in Response to Low Temperatures.

BACKGROUND: Antimicrobial peptides (AMPs) constitute the insect innate immune defense system. AMP production is usually induced by microbes. However, mounting evidence links insect immune reaction to cold hardiness.

OBJECTIVE: We aimed at characterizing two attacins, MpAtt1 and MpAtt2, from the desert beetle Microdera punctipennis in Coleoptera and investigating the expression profiles of the two genes in response to cold stress.

RESULTS: Full lengths MpAtt1 and MpAtt2 cDNAs were obtained from low temperature transcriptomic data. The newly identified attacins show characteristics different from those previously reported in other insects. MpAtt1 and MpAtt2 encode precursor proteins of 151 and 166 amino acid residues, respectively. These two attacins show 28.1% identity at amino acid level, and 38.3% identity at nucleotide level. Phylogenetic tree shows that the Mp attacins and the other Coleoptera attacins diverge earlier than Diptera and Lepidoptera attacins in evolution. The results of real-time quantitative PCR showed that MpAtt1 and MpAtt2 are highly expressed in hindgut plus Malpighian tube, and MpAtt1 also highly expressed in fat body. The mRNA levels of MpAtt1 and MpAtt2 were increased when the insects were treated at 4 degree C and a4 degree C, but the responsiveness to -4 degree C was lower than to 4 degree C.

CONCLUSION: The cold inducible expression of attacin genes from the desert beetle M. punctipennis from the aspect of antimicrobial peptide synthesis supports the hypothesis that the insect immune system is stimulated during cold exposure.