Keith B. Kofoed
Horizontal Gene Transfer Responsible for Carotenoid Production in Aphids
Horizontal Gene Transfer
Horizontal gene transfer (referred to as HGT for the rest of the paper) is said to have occurred when an organism successfully incorporates genetic information from another organism into its own genetic makeup when the first organism is not the offspring of the other organism. HGT, or lateral gene transfer (LGT), is used to describe both the artificial and natural transfers of genetic information from one organism to another. The flow of genetic information is thought to occur relatively frequently between microorganisms. Current evidence suggests that roughly 2% of genetic information in microorganisms is acquired though HGT. While significant it is is not widely believed to be enough to require changes to the current organization of phylogenetic trees. The transfer of genetic information is not limited by species, kingdom or even domain and can occur between species that are very different.
Within the kingdom of Bacteria HGT has been observed to function in three ways. The first is referred to as bacterial transformation and is caused by the alteration of a cell, which results in the uptake and expression of foreign DNA. Transduction is the process by which DNA from one bacterium is transferred to another bacterium through a virus, which infects one taking genetic information and then the other, depositing the genetic information. The final way HGT occurs is though a process known as conjugation. Conjugation is a form of bacterial “mating” which results in the sharing of genes. This process is common among bacteria of the same species but occurs with less frequency between bacteria of different species.
While evidence for HGT in microbes is abundant, evidence for HGT in higher order multicellular organisms is uncommon. As such the mechanisms by which HGT occurs from microbes to plants and microbes to animals has not been verified. However, it is speculated that HGT occurs in multicellular organisms in much the same way as it does between microbes.
Horizontal gene transfer has not been observed first hand in multicellular organisms. However, there is strong evidence to support that it has happened in the past. The most widely accepted occurrence of HGT in eukaryotic cells occurred after an early eukaryotic cell engulfed an alpha-protobacteria and maintained it as a symbiont. Eventually the symbiotic relationship proved so successful that the bacteria shed much of its genetic information, along with its ability to live on its own, and transferred segments of genetic information to the host cell.
Recently researchers have found strong evidence suggesting that Acyrthosiphon pisum, commonly known as the pea aphid, is utilizing genes most likely taken from an ancient fungal symbiont for the production of carotenoids.
Acyrthosiphon pisum, the pea aphid
| A. pisum
Acyrthosiphon pisum, or the pea aphid, belongs to the family Aphididae. The pea aphid is of significant agricultural importance because of the annual destruction it causes to crops. A. pisum is also of biological importance because its genome has been completely mapped and it is bred easily in laboratory conditions, making it a model organism.
Acyrthosiphon pisum is found through out the world on all continents with the exception of Antarctica. Aphids live on the plants they choose for food, typically on the underside of the leaves. Aphids are incredible host specific and speciation has occurred in relation to the host plants of choice. A. pisum prefer the pea plant, thus its common name, and relatives of the pea plant such as, alfalfa, clover, broad bean and other...
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