Studies On Molecular Evolution Of The Antimicrobial Peptide Genes Of Social Insects

Social insects have beening exsisted on the earth for more than 100 million years, which provide an excellent model for us to study the molecular evolution.We chose four species of social insect as materials,including three termite.species {Odontotermes formosanus(Shiraki),Macrotermes barneyi Light and Reticulitermes chinensis Snyder) and one honeybee species(Apis cerana Fabricius).We designed primers according to the reported antimicrobial peptide cDNA genes,and amplified the cDNA genes from the constructed cDNA libraries using Reverse Transcript PCR (RT-PCR),and then analyzed these sequences data using bioinformatics softwares.The results and conclusions are summarized as follows:(1) Totally O.formosanus has 56 different Termicin cDNA genes encoding 46 different Termicin peptides,M.barneyi has 54 different Termicin cDNA genes encoding 37 different Termicin peptides,and R.chinensis has 38 different Termicin cDNA genes encoding 21 different Termicin peptides.(2) The values of dN/dS of the Termicin precursor genes are > 1 in O.formosanus and M.barneyi,indicating that the Termicin genes undergo positive selection in these two termte species,and the microenvironmental pressure of these two kinds of termites are positive microenvironmental pressure.The value of dN/dS in R.chinensis is < 1,indicating that the Termicin gene in R.chinensis is under negative selection, and the microenvironmental pressure of this kind of termite is negative microenvironmental pressure.The values of dN/dS of the Termicin mature region of O.formosanus and M.barneyi are bigger than those of the Termicin precursor genes, which suggest that the microenvironmental pressure are mainly on the mature region.(3) A.cerana has totally 87 different antimicrobial peptide cDNA genes encoding 26 different antimicrobial peptides,among which,29 different genes are Defensin genes encoding 7 different Defensin peptides,11 different cDNA genes are Abaecin genes encoding 2 different Abaecin peptides,13 different cDNA genes are Apidaecin genes encoding 4 Apidaecin peptides and 34 different cDNA genes are Hymenoptaecin genes encoding 13 different Hymenoptaecin peptides.(4) As compared with the Western honeybee Apis mellifera L.,the Asiatic honeybee has more variable antimicrobial peptide genes(87 versus 16) and antimicrobial peptides(26 versus 11),especially the Hymenoptaecin genes(34 versus 2) and the Hymenoptaecin peptides(13 versus 1).This suggests that,compared to the Western honeybee that has a longer history of domestication,selection on the Asiatic honeybee has favored the generation of more variable antimicrobial peptides as protection against pathogens.(5) The results of phylogenetic analysis show that all the genes in the same family are homogenetic genes.According to the rule of selfish-gene,we predicted that there may be pseudogenes or unnecessary genes in the antimicrobial peptide genes,and these genes would be eliminated in the long term of evolution.