Discovery of jumping gene cluster tangles tree of life

Feb 04, 2011
These are Vanderbilt evolutionary biologists Antonis Rokas, right, and Jason Slot. Credit: John Russell, Vanderbilt University

Since the days of Darwin, the "tree of life" has been the preeminent metaphor for the process of evolution, reflecting the gradual branching and changing of individual species.

The discovery that a large cluster of genes appears to have jumped directly from one species of fungus to another, however, significantly strengthens the argument that a different metaphor, such as a mosaic, may be more appropriate.

"The are telling us something important about evolution … something we didn't know," said Antonis Rokas, assistant professor of biological sciences at Vanderbilt. He and research associate Jason Slot reported their discovery in the Jan. 25 issue of the journal Current Biology.

Rokas and Slot discovered that millions of years ago, a cluster of 23 genes jumped from one strain of mold commonly found on starchy foods like bread and potatoes, Aspergillus, to another strain of mold that lives in herbivore dung and specializes in breaking down plant fibers, Podospora.

The findings came as a major surprise, as there are only a handful of cases in recent evolutionary history where this type of between organisms, known as horizontal gene transfer, has been reported in complex cells like those found in plants, animals and fungi.

"Because most people didn't believe that such large gene clusters could be transferred horizontally, they haven't looked for them and they haven't been found," Rokas said.

Rokas and Slot detected the unprecedented gene cluster transfer during a detailed comparison of the entire genomes of nearly 100 species of fungi. The primary goal of their research is to identify the most reliable methods for determining the evolutionary relationships of species of all kinds. In the course of their analysis, they discovered the 23-gene capture.

The cluster codes for a toxic compound called sterigmatocystin. Cells produce this type of compound to attack competing organisms or to protect themselves from attacks. As a result, these types of compounds are the source of a number of important drugs, like penicillin and cyclosporin, as well as a number of natural poisons.

"Fungi produce an astonishing variety of drugs and poisons. Our discovery that one of the largest gene clusters responsible for making such a poison moved intact between species suggests that horizontal transfers of wholesale pathways may have contributed significantly to the generation of this diversity," Rokas said.

In the past, evolutionary research has focused on the passage of from parent to child, known as vertical gene transfer. This process, acted out over the eons of geological time, gives rise to the branching structure of the tree of life.

Since the 1980's, however, evolutionary scientists have become increasingly aware that horizontal or lateral gene transfer also plays a major role in evolution. In vertical gene transfer, all the genetic material in each new species come from a single ancestral species. In horizontal gene transfer, by contrast, species that receive bits of genetic material from its neighbors are directly related to a number of often unrelated species.

Horizontal gene transfer was first discovered in bacteria, and has been recognized as largely responsible for the problem of drug resistance. If one bacterium evolves a method for surviving a drug, this ability can spread rapidly to other unrelated microorganisms via horizontal gene transfer, substantially reducing the drug's effectiveness.

Though researchers now generally agree that horizontal gene transfer is relatively common among simple organisms like bacteria, they have continued to assume that it remained relatively rare among complex organisms like plants and animals.

"The thinking has been that there is very little horizontal gene transfer among plants and animals except for a few big, ancient events and maybe the occasional transfer of a single gene here or there," Slot said. "Our discovery suggests that the horizontal transfer of gene clusters may have been a big player not only in the evolution of bacteria but also in more complex organisms."

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gwrede
3 / 5 (2) Feb 05, 2011
An article about the mechanics of horizonal gene transfer would be nice.
docmaas
not rated yet Feb 05, 2011
But when an antibiotic is removed why do the bacteria regress to their sensitivity to the antibiotic over time? Aids drugs are used intermittently because the virus reverts. This has been adduced as an example of natural selection.

Do the leaping genes not integrate into the genome? If so why would the genome regress so quickly?

Is it because the new genes are quickly overrun by the fitness of individuals without the genes? If that is the case why are they less fit when the antibiotic they provide resistance do is removed?

Mike
Skeptic_Heretic
not rated yet Feb 05, 2011
Is it because the new genes are quickly overrun by the fitness of individuals without the genes? If that is the case why are they less fit when the antibiotic they provide resistance do is removed?

Mike

There's always a cost to horizontal gene transfer. In this case it si most likley that the inclusion of the new genes is detrimental to overall health, however provides resistance to an otherwise fatal environment.

Probably the closest comparison I can make is poison tolerance in humans. Getting a microdose of strychnine from something like smoking tobacco will make you semi-imune to the effects of a larger dose but it creates an addiction, a chemical need for the substance.
sstritt
1 / 5 (1) Feb 05, 2011
In light of this, wouldn't it be wise to reassess the wisdom of introducing GMO's into the environment?
Djincs
1 / 5 (1) Feb 05, 2011
An article about the mechanics of horizonal gene transfer would be nice.


Viruse can play this role(retro virus like herpes for example), imagine that this swine flue has fragment from the pig, then this virus affect a pregnant woman and virus affect the embrio in early stage, then this embrio can carry this genes even in the sperm/egg cells. I am shure this is much more common than we think(we are witnessing a chiken and a swine flue for such a short period of time(our existance) and imagine millions of years now) and it is a matter of time new things to be discovered, then the GM opposition will be much more pointless and the haters will look even more stupid than they are today!
kevinrtrs
1 / 5 (2) Feb 07, 2011
How long before they start admitting that it points more to a common designer re-using the same design pieces in different places?

That should be obvious to anyone looking at the data itself.

However, since there is no place for God[the uber intelligent designer], the researchers are forced to come up with the most ridiculous proposals to make the evidence fit the picture they have to paint.
Skeptic_Heretic
not rated yet Feb 07, 2011
How long before they start admitting that it points more to a common designer re-using the same design pieces in different places?
Keep waiting.
That should be obvious to anyone looking at the data itself.
Funny how god and jesus don't just jump out at you from DNA.
However, since there is no place for God[the uber intelligent designer]
Who's so lazy he has to reuse his kinects because "common design/common designer" like you pound requires your designer to be uncreative and uninspired.

Kev, why would your all powerful god use DNA at all?