Positive selection on termicins in one termite species, Macrotermes barneyi (Isoptera: Termitidae).

Termicin is a defensin-like antimicrobial peptide from termites which shows strong antifungal activity. All the termicin mRNA sequences (54 different mRNA sequences) of Macrotermes barneyi, which encoded 37 different termicin peptides, were amplified and identified by Reverse Transcript PCR (RT-PCR) with primers designed according to the reported termicin mRNA sequences. Comparison of the relative fixation rates of nonsynonymous (amino acid altering) and synonymous (silent) mutations (dN/dS > 1) indicates that strong positive selection exists on termicins of M. barneyi. Though high conversion exists in M. barneyi termicin mRNA, especially in the signal region, 10 positively selected sites were detected and identified from the mature region. Our results suggest that strong positive pressure from the complicated microbial environment drive the termite to generate more new peptides to defend against the pathogens' invading.