Friday, April 30, 2010

Fungus-Derived Genes Make Aphids Red

Carotenoids are pigments produced by many organisms, among them bacteria, plants, algae, and fungi. They're what gives carrots, red leaves, and some flowers their reddish/orange color. However, no animal has been known to produce them or to have the metabolic pathways required for carotenoid biosynthesis, until now.

In Science, Nancy Moran and Tyler Jarvik report the discovery of carotenoid biosynthesis genes in the genome of the pea aphid, Acyrthosiphon pisum, which has a body color polymorphism (some individuals are red, others are green). It was formerly thought that they got their pigmentation from their diet, or from their bacterial gut symbionts. Suspicions were raised, however, when no trace of a carotenoid pathway could be found in the primary bacterial symbiont of aphids, Buchnera, which is among the best-studied of bacterial symbioses, and in two other symbiont bacteria. Because the genome of the pea aphid was recently released, they searched for, and found, carotenoid synthesis genes, which are most closely related to similar genes in the fungi. This led them to conclude that aphids have gained the carotenoid biosynthesis pathway by lateral gene transfer from fungi.

Lateral gene transfer (also horizontal gene transfer) was long thought to be a rare or exceptional phenomenon, but this adds one more example to a growing list of transfer events which have been uncovered by new genomic methods.

Moran & Jarvik, Lateral Transfer of Genes from Fungi Underlies Carotenoid Production in Aphids, Science 328, 624-627 (30 Apr 2010). (DOI: 10.1126/science.1187113)
Takema Fukatsu, Perspectives: A Fungal Past to Insect Color, Science 328, 574-575 (30 Apr 2010).

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