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Can parasitic plants use hosts’ genes against them?

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Orobanche cumana (right) parasitizing a sunflower (left)/Christopher Clarke, Penn State

From ScienceDaily:

Sneaky parasitic weeds may be able to steal genes from the plants they are attacking and then use those genes against the host plant, according to a team of scientists.

In a study, researchers detected 52 incidents of the nonsexual transfer of DNA — known as horizontal gene transfer, or HGT — from a host plant that later became functional into members of a parasitic plant family known as the broomrapes, said Claude dePamphilis, professor of biology, Penn State. The transferred genes then became functional in the parasitic species. Although considered rare in more plants and other complex species, like plants, HGT may thus occur in some parasitic plants, an insight that could lead to better methods of controlling parasitic plants that threaten agriculture, he added.

“These parasitic plants that we study from the broomrape family include some of the the world’s most devastating agricultural weeds,” said dePamphilis. “The HGT discovery is really part of our effort to try to better understand how parasitic plants work and how we can better control them. Our hope is that we can use this information to find the best strategies to generate, or breed, resistant host plants.”

The researchers, who released their findings in the current issue of Proceedings of the National Academy of Sciences, suggest that the transfer could boost the parasitic plant’s ability to invade their hosts and overcome defenses the host creates to try to ward off attacks. HGT may also help reduce the risk of infection for the parasites. Paper. (paywall) – Zhenzhen Yang, Yeting Zhang, Eric K. Wafula, Loren A. Honaas, Paula E. Ralph, Sam Jones, Christopher R. Clarke, Siming Liu, Chun Su, Huiting Zhang, Naomi S. Altman, Stephan C. Schuster, Michael P. Timko, John I. Yoder, James H. Westwood, and Claude W. dePamphilis. Horizontal gene transfer is more frequent with increased heterotrophy and contributes to parasite adaptation. PNAS, October 2016 DOI: 10.1073/pnas.1608765113 More.

Right now, the researchers are not sure. If confirmed, it would be no surprise.

For some reason, the story puts one in mind of British science broadcaster Gordon Rattray Taylor (1911-1981) who died before his book The Great Evolution Mystery, repudiating Darwin, was published. In his case, one factor was the way the flatworm seizes and uses the weapons of its pond hydra victims:

The hydra is usually safe from the flatworm, but every so often a flatworm seeks out and consumes a hydra. The worm somehow swallows the hydra’s poison gun apparatus without digesting it, and then positions the guns on its own surface. It uses the guns for its own protection; one species actually fires them like rockets at assailants.

As long as the flatworm has ammunition from a previous meal, it ignores hydras. However, when it is low on ammunition, it finds another hydra, eats it, and repeats the cycle.

Taylor asks how a creature with no brain or complex nervous system learns this routine. How does it remember and pass it on? He writes: “The theory of evolution by natural selection is powerless to explain how chance variation could have evoked such a closely coordinated programme.” – By Design or by Chance?, p. 93

At least he did not live to hear all the ridicule heaped on researchers who dared to make such an obvious point in the succeeding Age of Dawkins.

See also: Horizontal gene transfer: Sorry, Darwin, it’s not your evolution any more

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Welcome to the world of the flatworm:

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