Lateral Transfer of Genes from Fungi Underlies Carotenoid Production in Aphids
Nancy A. Moran and Tyler Jarvik
Carotenoids are colored compounds produced by plants, fungi, and microorganisms and are required in the diet of most animals for oxidation control or light detection. Pea aphids display a red-green color polymorphism, which influences their susceptibility to natural enemies, and the carotenoid torulene occurs only in red individuals. Unexpectedly, we found that the aphid genome itself encodes multiple enzymes for carotenoid biosynthesis. Phylogenetic analyses show that these aphid genes are derived from fungal genes, which have been integrated into the genome and duplicated. Red individuals have a 30-kilobase region, encoding a single carotenoid desaturase that is absent from green individuals. A mutation causing an amino acid replacement in this desaturase results in loss of torulene and of red body color. Thus, aphids are animals that make their own carotenoids.
“A survey of the draft aphid genome identified more than 10 genes of lateral transfer origin. However, the carotenoid synthetic genes were overlooked because the survey was designed to detect bacterial genes in the eukaryotic genome. In comparison with prokaryote-prokaryote and prokaryote-eukaryote lateral gene transfers, less attention has been paid to eukaryote-eukaryote lateral gene transfers. Although such transfer events might have been relatively rare, the recent explosive accumulation of eukaryotic genome information opens a new window to lookinto unexplored dynamic evolutionary processes.”
Science 30 April 2010:
Vol. 328. no. 5978, pp. 624 – 627
DOI: 10.1126/science.1187113
PERSPECTIVES, EVOLUTION:
A Fungal Past to Insect Color
Takema Fukatsu
Many animals recognize and respond to the environment, foods, and enemies by making use of visual cues. Hence, animal body color is an ecologically important trait, often involved in prey-predator interactions through mimicry, aposematism (colors that warn), and crypsis (camouflage) (1). In the pea aphid Acyrthosiphon pisum, an insect that destroys plants by feeding on the sap, red and green color insects frequently coexist in natural populations (see the figure). Among its major natural enemies, lady beetles preferentially attack red aphids on green plants (2), whereas parasitoid wasps deposit eggs in green aphids more frequently (3). It has been hypothesized that these opposite predation and parasitism pressures maintain the color variation in natural aphid populations. This represents one of the classical views on the evolutionary ecology of animal color polymorphism (1). On page 624 of this issue, Moran and Jarvik (4) report an unexpected layer interwoven under this well-known evolutionary scenario: Genes transferred from a fungus to the aphid genome underlie the red and green coloration.
National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8566, Japan.
Science 30 April 2010:
Vol. 328. no. 5978, pp. 574 – 575
DOI: 10.1126/science.1190417
The Pundit’s thoughts:
Golden Rice, Golden Sorghum, Golden Banana, and now the Natural Golden Aphid.
