Evolution and function of a cytochrome P450 cluster in deltamethrin resistance of the red flour beetle, Tribolium castaneum

Cytochrome P450s play an important role in the detoxification of xenobiotics and metabolizing endogenous compounds. P450 genes are thought to be generated from a series of gene duplications followed by differentiation. A P450 gene, CYP6BQ9, from Tribolium castaneum is responsible for the majority of deltamethrin resistance in QTC279 resistant strain. This gene is a member of a 12-gene cluster. To determine the evolution and function of members in this cluster, the phylogenetic relationship of clustered genes, tissue specific expression, differential expression between resistant and susceptible strains, induction of these genes by deltamethrin in resistant strain, and RNA interference (RNAi) aided knock-down in the expression of clustered genes on the deltamethrin resistance were investigated. Our study revealed 12 clustered genes fall into 4 clans. Nonfunctionalization occurred in clan II. The genes in clan III and IV may have undergone subfunctionalization after gene duplication with maintenance and/or refinement of the ancestral function of detoxification. The expanded tissue expression of clan III genes and the midgut specific expression of CYP6BQ11 suggest that these genes probably have acquired novel functions. RNAi experiments showed that four other genes in this cluster also play important roles in deltamethrin detoxification although they are not as important as CYP6BQ9.