the communications weaponry system of dodder, which operates much like a
computer virus, could provide researchers with a method to engineer
a parasitic plant that levies millions of dollars' worth of damage on
crops each year is a stealthy invader with the ability to wage war on
the genes of its host plants. The assailant utilizes a highly
sophisticated method of disarming its victims involving cross-species
gene manipulation that has never before been seen from a parasitic
plant. Understanding dodder's covert communications weaponry system,
which operates much like a computer virus, could provide researchers
with a method to engineer parasite-resistant plants.
paper describing the research by a team of scientists from Virginia
Tech and Penn State appeared this week in the journal Nature.
big news is that we now have evidence of a function for RNA that is
being exchanged between dodder and its quarry," said Jim Westwood,
professor of plant pathology, physiology, and weed science in Virginia
Tech's College of Agriculture and Life Sciences, an author of the paper.
had previously learned that messenger RNA, a nucleic acid present in
all living cells whose primary role is to act as a messenger carrying
instructions from DNA, moves between parasitic plants and their hosts,
but we have yet to discover the significance of this exchange. But when
we looked at microRNA, we found that dodder also passes this chopped-up
form of RNA into its prey, which then exerts control over the host's
a battle between host and parasite.. In this case, dodder is trying to
hack into the host's information system and the host is trying to shut
it off. MicroRNAs are a new class of weapon being used in the warfare,"
are short bits of nucleic acid -- the material of DNA and RNA -- that
can bind to messenger RNAs that code for protein because they have a
complimentary sequence of A, U, C and G. This binding of microRNA to
messenger RNA prevents the protein from being made, either by blocking
the process directly or by triggering other proteins that cut the
messenger RNA into smaller pieces. Importantly, the small remnants of
the messenger RNA can then function like additional microRNAs, binding
to other copies of the messenger RNA, causing further gene silencing.
team found that microRNAs have a more powerful function than previously
believed. The scientists investigated the parasite's microRNAs as they
entered the host and discovered that microRNAs are shutting off specific
genes in the host plant. Evidence points to the fact that these
targeted genes are the same genes a parasite would need to silence in
order to establish dominance.
interaction involves the use of microRNAs as messengers of doom. They
are hijacking information from the host," said Westwood, who is
affiliated with the Fralin Life Science Institute. "We don't yet know
how they are being exchanged in terms of the mechanism, but it seems
that many different organisms, including plants, fungi and insects, are
using microRNAs as remote signals against other organisms. In these
cases, the pathogen is sending microRNAs to shut down the host's
defenses. Likewise, the host is shooting its own microRNAs into the
pathogen. MicroRNAs are a new class of weapon being used in the
This research builds on previous
studies by Westwood. The first, published in August 2014 in Science
magazine, presented the discovery of a novel form of inter-organism
communication using messenger RNA, showing that plants share an
extraordinary amount of genetic information with one another. The
second, published in November 2016 in the Proceedings of the National
Academy of Sciences, presented the discovery that parasitic weeds may be
able to steal genes from their prey and then use those genes against
the host plant.
When a plant is attacked by a
parasite it initiates a number of defense mechanisms. In one of these
mechanisms, similar to blood clotting after a cut, the plants produce a
protein that clots the flow of nutrients to the site of the parasite.
MicroRNA from dodder targets the messenger RNA that codes for this
protein, which then helps to maintain a free flow of nutrients to the
parasite. The gene that codes for this clotting protein has a very
similar sequence across many plant species, and the researchers showed
that the microRNA from dodder targets regions of the gene sequence that
are the most highly conserved across plants. Because of this, dodder can
probably silence this clotting protein in, and therefore parasitize, a
wide variety of plant species.
researchers sequenced all of the small RNAs in tissue from the parasite
alone, the host plant alone, and a combination of two. By comparing the
sequencing data from these three sources, they were able to identify
microRNAs from dodder that had entered the plant tissue. They then
measured the amount of messenger RNA of genes that were targeted by the
dodder microRNAs and saw that the level of messenger RNA from the host
was reduced when the dodder microRNAs were present.
with previous examples of small RNA exchange between fungi and plants,
our results imply that this cross-species gene regulation may be more
widespread in other plant-parasite interactions," said Michael J.
Axtell, professor of biology at Penn State and an author of the paper.
"So, with this knowledge, the dream is that we could eventually use gene
editing technology to edit the microRNA target sites in the host
plants, preventing the microRNAs from binding and silencing these genes.
Engineering resistance to the parasite in this way could reduce the
economic impact of the parasite on crop plants."
addition to Westwood and Axtell, the research team included Gunjune
Kim, a former post-doctoral student from Chicago and Vivian
Bernal-Galeano, a graduate student from Colombia, at Virginia Tech;
Saima Shahid, Nathan R. Johnson, Eric Wafula, Feng Wang, Ceyda Coruh,
and Claude W. dePamphilis at Penn State; and Tamia Phifer at Knox
The research was funded by the U.S.
National Science Foundation and the U.S. National Institute of Food and
Agriculture. Additional support was provided by the Penn State Huck
Institutes of the Life Sciences.
AAAS and EurekAlert! are not responsible for the accuracy of news
releases posted to EurekAlert! by contributing institutions or for the
use of any information through the EurekAlert system..