Parasitic plants may form weapons out of genes stolen from ...

Parasitic plants may form weapons out ofgenes stolen from hosts24 October 2016

Orobanche cumana (right) is parasitizing a sunflower(left). Credit: Christopher Clarke, Penn State

Sneaky parasitic weeds may be able to stealgenes from the plants they are attacking and thenuse those genes against the host plant, accordingto a team of scientists.

In a study, researchers detected 52 incidences ofthe nonsexual transfer of DNA—known as horizontal gene transfer, or HGT—from a host plantthat 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 becamefunctional in the parasitic species. Althoughconsidered rare in most plants and other complexspecies, HGT may thus occur in some parasiticplants, an insight that could lead to better methodsof controlling parasitic plants that threatenagriculture, he added.

"These parasitic plants that we study from thebroomrape family include some of the the world'smost devastating agricultural weeds," saiddePamphilis. "The HGT discovery is really part ofour 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 findthe best strategies to generate, or breed, resistanthost plants."

The researchers, who released their findings today(Oct. 24) in the current issue of Proceedings of theNational Academy of Sciences, suggest that thetransfer could boost the parasitic plant's ability toinvade their hosts and overcome defenses the hostcreates to try to ward off attacks. HGT may alsohelp reduce the risk of infection for the parasites.

Striga asiatica is shown on sorghum in Malawi-Tanzania2011. Credit: Mike Timko

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While horizontal gene transfers in less complexspecies, such as bacteria, are common, mostevolution in more complex organisms is driven bythe sexual exchange of DNA, along with mutationand natural selection. However, the researcherssuggest that the close feeding connections ofparasitic plants with their hosts may increase thechances of intact genes traveling from the host tothe parasite's genome where it can quickly becomefunctional.

"Parasitic plants seem to have a far greater rate ofhorizontal gene transfer than non-parasitic plantsand we think this is because of their very intimateconnection they have with their host," saiddePamphilis.

The roots of the parasite contact and enter thehost, and then begin extracting water, sugars,mineral nutrients and even nucleic acids, includingDNA and RNA, he added.

"So, they are stealing genes from their host plants,incorporating them into the genome and thenturning those genes back around, very often, as aweapon against the host," said dePamphilis.

Triphysaria eriantha field with wild grasses and other hostplants in California. Credit: Huiting Zhang

Farmers throughout the world struggle with these

types of parasitic plants, which are so numerous insome areas of the world that they become a majorsource of crop loss. In Sub-Saharan Africa, forexample, Striga—or witchweed—is one of the mostdamaging sources of agricultural loss, according todePamphilis.

To detect HGT in the plants, the researchers useddata generated by their collaborative research effortfunded by the U.S. National ScienceFoundation—the Parasitic Plant Genome Project—togenerate evolutionary histories for thousands ofgenes in the parasitic plants, said dePamphilis.

The researchers focused ontranscriptomes—expressed gene sequences—ofthree parasitic plants:, Triphysaria versicolor, alsocalled yellowbeak owl's-clover; Striga hermonthica,or giant witchweed; and Phelipanche aegyptiaca,called Egyptian broomrape, as well as thenonparasitic plant Lindenbergia philippensis, andgenome sequences from 22 other nonparasiticplants. Because the researchers consideredmRNA, which can move between hosts and theirparasites, as a possible source of the transfers,they tested and re-tested the data to rule out theexperimental host as the source of the geneticmaterial. Instead, they found that the foreignsequences had been derived from entire genes ofpast host plants and incorporated into the parasiticplants genomes.

Future research may investigate the mechanism ofhorizontal gene transfer to help engineer improvedplant defenses against parasitic attacks,dePamphilis said.

More information: Horizontal gene transfer ismore frequent with increased heterotrophy andcontributes to parasite adaptation, Proceedings ofthe National Academy of Sciences, www.pnas.org/cgi/doi/10.1073/pnas.1608765113

Provided by Pennsylvania State University

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APA citation: Parasitic plants may form weapons out of genes stolen from hosts (2016, October 24)retrieved 28 May 2022 from https://phys.org/news/2016-10-parasitic-weapons-genes-stolen-hosts.html

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