Abstract:  Cold acclimation usually alters gene expression in insects. Extensive studies from the genomic level will help to fully understand the molecular mechanism of insects in response to cold. In order to get the further information about the up-regulated attacin gene (MpAttacin1) obtained from the transcriptomic data generated at 4℃ from the desert beetle Microdera punctipennis, and to analyze the responsive expression of this gene induced by low temperature, MpAttacin1 was characterized by bioinformatic analysis. Real-time quantitative PCR was performed to detect the mRNA level of MpAttacin1 at low temperatures. The results showed that the obtained MpAttacin1 cDNA is 523 bp with an open reading frame of 456 bp and the 5′-untranslated region of 66 bp. It encodes a polypeptide of 151 amino acid residues containing a putative signal polypeptide of 17 amino acids at the N terminal end. Homology analysis showed that the encoded product of this gene shares 30%-40% identity at the amino acid level with attacins from other insects of Lepidoptera, Diptera, and Coleoptera. The phylogenetic tree generated by Neighbor-Joining method indicated that MpAttacin1 and attacin proteins from other coleopterans are descended from a common ancestor, and they belong to Attacin_C superfamily. Analysis of realtime quantitative PCR showed that the expression of MpAttacin1 presented a stress-response tendency when stressed at both 4℃ and -4℃, increasing first and then decreasing. However, there were differences in their responsive time and strength between these two treatments. The mRNA level of MpAttacin1 at 4℃ for 5 h and 9 h was 2.3- and 3.8-fold as high as that of the control at room temperature, respectively, while that at -4℃ for 7 h and 9 h was 2.4- and 1.5-fold as high as that of the control, respectively. The results suggest that in addition to the typical function as an anti-microbial peptide, attacin may also be involved in cold adaptation in insects.

Key words: Desert insect, Microdera punctipennis, cold-responsive genes, attacin, low temperature, antibacterial peptide, expression profiling