Adaptive Evolution Analysis of the GTPase Effector Domain of Avian Mx Gene

The objective of this study was to trace the route of avian Mx gene evolution and the variations of its structure and function.Nucleotide sequences of Mx gene GED domain(GTPase effector domain) were amplified by PCR and sequenced for four economical types in a total of eleven Chinese indigenous chicken breeds.The chicken breeds included HY,QY,WC,TB,LS,SG,BY,XI,LU,BA and SK.The reported sequences of Jungle fowls,some galliform and anseriform avians were also used in this study.mrModeltest and MrBayes were used to select the best nucleotide substitution model and construct the evolutional tree.Datamonkey and PAML4b were used to test the selective pressure on amino acid sites of Mx gene GED domain.Mx gene GED sequences of Chinese indigenous chicken breeds were properly obtained,with a length of 231 bp,which encoded 77 amino acids.Multiple sequence alignment results showed that Mx gene GED sequences of domestic jungles were highly conservative;only three polymorphic sites were identified,which located in 203 2 bp,207 5 bp and 213 9 bp,respectively.AIC information criterion showed that the best nucleotide substitution model of avian Mx gene GED was "GTR+G".The Bayes evolutional tree based on this best model had higher posterior probability and which revealed the phylogenetic relationships were basically the same as the evolution of avian species.Single breakpoint scanning and genetic algorithm scanning by Datamonkey found no recombination events in avian Mx gene GED sequences.The site selection pressure test showed that avian Mx gene GED sequences had not suffered positive selection pressure.