A Plant Pathologist Takes
on Tall Fescue’s Endophyte
by Randy Weckman
Don't ask plant pathologist Chris Schardl about tall fescue
grass unless you've brought your lunch along — and maybe
dinner, too. Schardl is a world-renowned expert on tall fescue
and its symbiotic friend, an endophyte fungus that lives inside
the plant between the plant cells.
H
is research focuses on the relationship
between the fungus and the grass. The plant nurtures and gives
sustenance to the fungus and, in return, the endophyte helps the
plant keep insects at bay, survive drought, and tolerate grazing
by livestock. Schardl plans to tinker ever so slightly with the
cozy relationship between the two to make the tall fescue-endophyte
system better for livestock.
 Tall
fescue is a popular forage grass, with millions upon millions
of acres of it growing from Wisconsin to Florida and from the
East Coast to Kansas and beyond. Because nearly all of these millions
of acres of fescue are infected with a fungal endophyte (which
is a word made up from Greek, meaning within the plant), the grass
has tremendous advantages over other common grazing grasses. But
it also holds a significant disadvantage for livestock. The endophyte,
with the scientific name of Neotyphodium coenophialum, can be
responsible for poor weight gain, hormonal imbalances that lead
to reduced fertility and lactation, birthing problems, and in
extreme conditions, gangrene of the animals' limbs. Overall, it
is estimated that tall fescue toxicosis may cost the livestock
industry roughly $1 billion annually.
"In the tit-for-tat relationship between the two, the endophyte
helps in a variety of ways, including drought tolerance, shoot
growth, tillering, seed production, seed germination, phosphorus
uptake, and resistance to nematodes and insects alike," Schardl
said.
The symbiotic relationship is many thousands of years old. In
fact, Schardl's group discovered that N. coenophialum shares a
relationship with other Neotyphodium species (also called Epichloe
species) in fescues and ryegrasses that are all over Europe and
northern Africa, but the tall fescue endophyte has a uniquely
complex origin as a hybrid of three other endophytes.
 As
a hybrid, the tall fescue endophyte brings together many beneficial
traits that ancestral endophytes evolved as symbionts of ancient
grass species. But like mules, which are the hybrid product of
horses and burros, the tall fescue endophyte cannot reproduce
sexually. Reproduction of the endophyte depends on its ability
to extend microscopic runners into each developing seed of the
tall fescue plant. When that seed germinates, the endophyte proliferates
throughout the new plant's tissues.
Keeping the Good, Removing the Bad
Schardl's research, funded by both the U.S. Department of Agriculture
and the National Science Foundation, is a two-pronged project to:
- Determine exactly how the fungus in fescue helps the plant.
- Manipulate the genetics of the fungus to keep the good qualities
while removing its ability to cause fescue toxicosis.
The plant pathologist believes that much has been accomplished
toward these aims. Schardl's group, along with other researchers
at UK and elsewhere, has shown how the endophyte starts the process
that leads to toxicosis in grazing animals. The fungus produces
three types of alkaloids. Of these, ergot alkaloid in the form
of ergovaline is the most likely culprit in toxicosis in grazing
animals.
 The
fungus also produces loline alkaloid and peramine alkaloid, both
of which help protect the fescue plant from insects and drought.
(Loline alkaloid is a natural insecticide. Peramine is rather
nasty tasting to insects, which helps the plant ward off invasion
from hungry insects.) Schardl also wants to see if loline alkaloid
helps tall fescue survive drought. Apparently neither loline alkaloid
nor peramine alkaloid is poisonous to grazing animals.
Schardl also has identified specific genes that control the production
of the three types of alkaloids. Each is triggered by a different
set of genes.
How did he do that?
Schardl's laboratory brings to bear the most current techniques
in biochemistry and molecular biology and the classical techniques
of Gregor Mendel and Thomas Hunt Morgan to find the alkaloid production
genes. For example, in a "reverse genetics" approach,
the researchers find out what chemical reactions are responsible
for each step in the complex pathway the endophyte uses to manufacture
each alkaloid. Then they find and analyze the biochemical catalysts
(enzymes) for each of those steps. Finally, they use knowledge
of the enzyme structure to find the genes that code for them.
(Genes are really sequences of DNA that come together in a particular
linear order to control the development of every cell in any living
thing.)
A parallel approach uses principles of evolution, earning for
Schardl a worldwide reputation as an expert in the evolution of
symbionts. Schardl started his work in the evolution of symbionts
by studying the origins of Neotyphodium species that are symbiotic
with wild grasses, which are related to tall fescue. In doing
so, he has discovered scores of new Neotyphodium species, some
of which produce the same alkaloids as the tall fescue endophyte
and some that don't.
By comparing the DNA sequences from different Neotyphodium species
in what amounts to a sophisticated process of elimination, his
group confirmed the identity of genes responsible for the production
of ergovaline, the alkaloid that is toxic to animals. This same
approach helped them find other genes that apparently direct the
endophyte to make loline and peramine alkaloids, which help protect
the plant from insects and drought.
The Next Step
Now that they've found the genes they were looking for, Schardl's
group plans to insert foreign DNA (the building blocks of genes)
in the middle of the gene that controls the production of ergovaline.
It is hoped the result will be that the gene will not be able
to express itself because of interferences from foreign DNA. This
would stop the endophyte from producing the ergovaline toxin.
Genes that control the other two alkaloids—the ones that
help protect the plant from insects and drought—would be
unaffected.
Schardl speaks about his work with confidence but without arrogance,
as if what he's already done is merely applying known techniques
to the problem described by other scientists. He is equally confident
that he will be able to disengage the specific gene in the endophyte
that causes fescue toxicosis while keeping the protective qualities
of the endophytic fungus intact.
Already, graduate students in his laboratory have disengaged
this gene in an endophyte of ryegrass (a first cousin to fescue)
and have shown that the modified endophyte was still a capable
symbiont.
Having put all the techniques in place and found the key genes,
Schardl's laboratory is now engineering out the ergot alkaloid
gene in the tall fescue endophyte. But why was time spent on a
ryegrass endophyte, if plans really were to apply the techniques
to tall fescue?
The answer is that the tall fescue endophyte, being a complex
hybrid—sort of like a mule—requires more than double
the time and effort needed to accomplish this task.
"It was necessary to show the U.S. Department of Agriculture
that we knew how to do this so they would fund our work on tall
fescue, which will cost more time and money than ryegrass,"
Schardl said.
The ryegrass system is being used to determine specifically the
costs, benefits, and risks of this kind of engineered product.
Meanwhile, Schardl's students are developing and testing more
sophisticated approaches to modify the tall fescue endophyte.
"Our new approach is intended to remove the gene we want
to remove yet have no foreign gene in its place," Schardl
said. "Although this may sound simple—and maybe someday
it will be—it actually requires us to make some additional
technological advances in fungal molecular biology," Schardl
said.
"The payback could be enormous. If we can eliminate the
endophyte's ability to manufacture ergovaline, we may greatly
improve the economics of pasturing livestock in Kentucky and much
of the eastern U.S.," he said.
The Stowaway Grass and Fescue War
T
all fescue grows throughout the South as the premier grazing grass.
The most common cultivar — which became known later as Kentucky
31 — was discovered in Menifee County, Kentucky, by University
of Kentucky agronomist E.N. Fergus in the fall of 1931, a year noted
for a severe drought. Fergus, in Frenchburg that day judging a local
sorghum syrup contest, heard from the clerk of the circuit court
about an amazing grass growing locally. Intrigued, Fergus asked
to see the grass growing on W.M. Suiter's farm. Fergus later admitted
that he didn't recognize the species. To his astonishment, the grass
was lush, green, and quite vigorous. Fergus noted that on that hillside
where the grass was growing there was virtually no erosion. He asked
for seed, which he brought back to Lexington. The grass performed
well in research trials and was officially named Kentucky 31. Because
of these characteristics, Kentucky 31 was planted throughout the
South and Midwest to provide grazing pasture and control erosion
on millions of acres.
 Kentucky
31 was so aggressive and hardy that it took over large regions
wherever it was planted. But soon, farmers noticed that livestock
grazing it sometimes didn't perform well, especially in hot weather,
and they raised questions about it. As a result, Kentucky 31 became
quite controversial within the College of Agriculture's agronomy
department, especially between two professors. One professor continued
to preach the blessings of the grass, while the other cursed it.
Fergus reported many years after his retirement that he was able
to stay out of the fray, but opined that avoiding the conflict
was difficult. Sometimes referred to as the Fescue War, the duel
over Kentucky 31, which was quite acrimonious and public, continued
from the late 1940s until the summer of 1952, when both antagonists
left the University of Kentucky. Subsequent to that, other University
of Kentucky agronomists continued to investigate the concerns
with Kentucky 31 fescue and helped establish the mechanism by
which fescue toxicosis is effected.
The fact that the grass found on W.M. Suiter's hillside in 1931
is not a native grass, but rather of European origins, is puzzling.
The story explaining how this European grass became established
in Menifee County is fascinating but well may be apocryphal. The
legend is that a shipment of bone chinaware from England arrived
in Menifee County sometime in the 19th century. Grass packing
material surrounded the fine china to help prevent breakage during
the long ship ride across the Atlantic. That stowaway grass was
tall fescue, and its own stowaway was the fungal endophyte. The
seed in the packing grass, perhaps planted on purpose or by accident,
became the progenitor of today's fescue, now growing on millions
of acres throughout the South. And despite tall fescue toxicosis,
the growth, persistence, drought tolerance, and suitability on
hillsides continue to make it a very popular grass.
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