Friday, October 27, 2006

Genome Buzz: Honeybee DNA

Scientists have officially unveiled the DNA code of the western honeybee, the first genome to be sequenced for an animal with ultrastratified societies.

The bees are among the select species in which a few individuals reproduce while others in the colony raise the young and do the chores.

The honeybee genome, the whole sequence of its DNA building blocks, shows some patterns that fit old ideas of social living plus some patterns that demand new thinking, reports the consortium of bee-genome researchers.

The scientists report the genome's highlights in the Oct. 26 Nature. More than 40 other analyses also appeared in journals including Science, the Proceedings of the National Academy of Sciences, and Genome Research.

"The sequencing of the honeybee genome is unquestionably a historic event," comments Ben Oldroyd, a bee specialist at the University of Sydney in Australia.

The honeybee's genome is the fifth to be sequenced among insects, says Gene Robinson of the University of Illinois at Urbana-Champaign, a founding member of the bee consortium. Geneticists first did the lab fruit fly, Drosophila melanogaster, and have since published reports on another fruit fly species, the malaria mosquito, and the silkworm.

Among the novelties of the honeybee, Apis mellifera, are its 170 genes for odor receptors. The lab fruit fly has 60. "Social life relies heavily on smell," notes Robinson.

The bees, however, carry fewer known immune system genes than the lab fruit fly or malaria mosquito does. That was a surprise, says Robinson, since social life brings extra risks of disease. Perhaps the honeybees compensate through particularly healthful behaviors, such as grooming, or perhaps some undiscovered genes drive their innate immunity. "Either way, it will be interesting," says Robinson.

The honeybees' famous royal jelly, the food that sets a larva on the road to becoming a queen instead of a worker, comes from proteins encoded by nine genes. The researchers compared them with other species' genes and concluded that they evolved from the so-called yellow gene, which plays a role in fruit fly pigment, for example.

In several groups of genes, such as those for circadian rhythms, the honeybee looks more like a vertebrate than the other sequenced insects. The honeybee also uses a full set of vertebratelike genes for enzymes that regulate the action of other genes. Lab fruit flies use a different system for regulating genes.

Even though honeybees differ radically from fruit flies in their sex determination—honeybee males develop from unfertilized eggs and thus have only one copy of each chromosome, whereas a fruit fly male gets chromosomes from both a father and mother—the two species' sex-related genes still show similarities.

Honeybees can perform remarkable feats of learning and memory, says Adrian Dyer of Monash University in Clayton, Australia. He predicts that having the honeybee genome in hand will spur "insight into how complex behavior patterns can arise in organisms with relatively simple brains."

The new research should also boost efforts to breed hardier honeybees, says Robinson. He says that U.S. commercial honeybee populations have shrunk by up to a third in the past 20 years, mostly because of an invasion of bee-killing mites.


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