Submitted to: Biomed Central (BMC) Genomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 12, 2013
Publication Date: December 23, 2013
Citation: Xu, J., Strange, J.P., Welker, D., James, R.R. 2013. Detoxification and stress response genes expressed in a western North American bumble bee, Bombus huntii (Hymenoptera: Apidae). Biomed Central (BMC) Genomics. 14:874-887. Interpretive Summary: Honey bees have been found to have few genes for detoxifying pesticides and other environmental toxins (such as plant toxins), fewer genes than some other common insects like flies. We wondered if bumble bees are similar to honey bees in this respect, considering that they are closely related, and they are both pollinators of a wide variety of flowering plants. To test this idea, we isolated and sequenced active genes (messenger RNA) from the Hunt bumble bee (Bombus huntii), and then determined which genes are thought to be important for detoxification and stress-repair functions. We evaluated genes from across all life stages, and found that the Hunt bumble bee has the genetic potential to produce a large number of proteins known from other insects to breakdown pesticides, or to repair damage from environmental stresses, including physiological injury caused by pesticides. However, the number of genes in these various biochemical pathways was substantially fewer than found in fruit flies, a model organism for genetic studies, and slightly fewer than are found in the honey bee. We did not identify all such genes present in DNA, but evaluate those genes that are actually activated (expressed). We also found that, generally, many more detoxification/stress related genes were expressed in adult females (workers and queens) than in adult males and larvae. The detoxification and stress related genes we identified from Hunt’s bumble bee tended to be intermediate between those found in fruit flies and honey bees, based on gene sequence similarity. Interestingly, the honey bee was found to have evolved some unique, closely related genes with a wide variety of functions, and these genes appear to have evolved after bumble bees and honey bees separated. Thus, both bees developed some detoxification functions that are similar, but that arose independently in each species.
Technical Abstract: Bumble bees are generalist floral visitors, meaning they pollinate a wide variety of plants. Their pollination activities expose them to both plant toxins and pesticides, yet little is known about what detoxification pathways are active in bumble bees, how the expression of detoxification genes changes across life stages, or how these genes are phylogenetically related to those in other insects. We developed a cDNA database using pyrosequencing of mRNA extracted from all life stages and castes, and found Bombus huntii (the Hunt bumble bee) expressed approximately 1068 genes associated with detoxification and stress responses, including oxidation and reduction enzymes, conjugation enzymes, hydrolytic enzymes, ABC transporters, cadherins, and heat shock proteins. The diversity of genes within some detoxification pathways varied among the life stages and castes, with generally fewer in adult males and larvae than in adult females. Phylogenetic comparisons among detoxification and stress related genes sequenced from B. huntii, the honey bee Apis mellifera, and the fruit fly Drosophila melanogaster, show B. huntii to have many genes with homology to these other insects. The sequences of detoxification/stress related genes we identified from B. huntii tended to be phylogenetically intermediate between gene sequences from D. melanogaster and A. mellifera, with a greater similarity to A. mellifera. Also, the numbers of genes identified in B. huntii was more similar to the honey bee than the fruit fly. However, both A. mellifera and D. melanogaster had clades with few or no orthologs to either B. huntii or each other, and this was particularly striking in the honey bee P450 and esterase genes.