UNIVERSITY PARK (Centre
Co.) Researchers at Penn State
and at Brookhaven National La
boratory have collaborated to
identify a gene that is directly
linked with a mechanism of plant
resistance to insect pests.
The discovery, which was des
cribed in an article published in
the Proceedings of the National
Academy of Science on Aug. 6,
could have important implications
for agriculture as well as other in
dustries.
David Schultz, who received
his Ph.D. in genetics from Penn
State’s College of Agricultural
Sciences in May of this year and is
a postdoctoral researcher at
Michigan State University, identi
fied the gene in collaboration with
June Medford, assistant professor
of biology and biotechnology in
Penn State’s Eberly College of
Science; Edgar Gaboon and John
Shanklin. both biochemists at
Brookhaven National Laboratory
in Upton, N.Y.; and Richard
Craig, J. Franklin Styer professor
of horticultural botany, Diana
Cox-Foster, associate professor of
entomology and Ralph Mumma,
distinguished professor of en
vironmental quality, all in Penn
State’s College of Agricultural
Sciences.
The isolation and identification
of the gene is the culmination of
years of interdisciplinary studies
at Penn State, beginning with re
search looking at the susceptibility
of garden geraniums to certain
kinds of spider mites and aphids.
Since the early 19605, Penn State
scientists have studied thousands
of plants to learn what makes
some geraniums resistant and
others susceptible to pests.
A grant from the U.S. Depart
ment of Agriculture in the late
1980 s and a four-year Penn State
Intercollege Grant beginning in
1990 supported the highly multi
disciplinary research effort, which
included horticulturists, plant
morphologists, entomologists,
geneticists, molecular biologists,
and biochemists.
The researchers determined that
resistant geraniums produce a vis
cous material from hairlike struc
tures, called trichomes, on their
stems and leaves. This material
impedes insects and mites in
several ways by trapping them
in the viscous liquid, by killing
them outright, and by inhibiting
the ability of females to lay eggs.
The viscous liquid contains com
pounds known as unsaturated ana
cardic acids, which are synthe
sized from un saturated fatty acids
in plants.
“Trichomes in both resistant
and susceptible plants produce
anacardic acids, but the difference
is that anacardic acids in resistant
plants are unsaturated,” said
CANCER!]
Surprisingly, many cancers are
caused by lifestyle patterns. If you
apply certain changes in your daily
living habits, you can avoid most
types of cancer. If you would like
more information, or to order our
cancer-avoidance strategies, call:
1-800-991-LIFE
< 1-800-991'5433 >
advanced lifestyle solutions®
Researchers ID
Schultz, who did his research in
June Medford’s laboratory. "Un
saturated anacardic acids form a
viscous liquid, like vegetable oil
so they stick to the insects.
You can feel these sticky sub
stances on the stems of the resist
ant geraniums. The saturated ana
cardic acids found on susceptible
plants are more solid, and do net
stick to insects.”
Before Schultz began his doc
toral studies at Penn State in 1992,
a group of students and postdoc
toral scholars working with Craig
and.Mumma had identified the
two unsaturated fatty adds thai
were die precursors to die unsatur
ated anacardic acids in the resist
ant geraniums. They also knew
that a single gene was responsible
for the formation of the unsatur
ated fatty acids. “My role was to
find that gene,” Schultz said.
Because the researchers knew
that the sticky compounds could
be found only in the trichomes,
they needed a method to ooiain
large quantities of them. Postdoc
toral scholar Ellen Yerger, work
ing in Diana Cox-Foster’s labora
tory, developed a method of re
moving the tiny trichomes from
the plants so that their genetic
makeup could be examined. By
freezing the parts of the plant cov
eted with trichomes in liquid ni
trogen and then vigorously shak
ing them, she could get the tri
chomes to break away from the
supporting plant tissue.
“This was crucial for my re
search because the -gene 1 was
looking fa could only be found in
these trichomes,” Schultz said. “It
took months to collect enough tri
chomes so that I could begin my
research. Without Ellen’s tech
nique, my work would have been
impossible.”
The type of gene Schultz was
looking for encodes a desaturase.
“It desaturates the fatty acid,
changing its molecular structure
by adding a double bond at a spe
cific point along the fatty acid’s
carbon chain,” Schultz said. “I
was looking for the desaturase
gene that leads to the production
of two fatty acids known as
16:1A" and 18:1A ,S .
“What we were hunting for was
a gene that looked like it had the
characteristics to convert fatty
acids in precisely the way neces
sary to create the unsaturated ana
cardic acids,” Schultz said. “We
also knew from previous research
that this gene would be expressed
only in the trichomes of the resis
tant plants and nowhere else
not in other parts of the plants, and
not in the trichomes of the sus
ceptible plants.”
Next, Schultz and Medford did
. RNA assays, which analyzed the
expression of genes in the tri
chomes of resistant geraniums, in
those of susceptible geraniums,
and In tissue from other parts of
the plants. They narrowed the
search to two genes that they
thought might encode the desatur
ase responsible for the production
df unsaturated fatty acids. “One of
the genes was a perfect match.”
said Medford. “We found it only
in the trichomes of the resistant
plants, and nowhere else. The
gene was present in all resistant
plants regardless of whether they
were parents, hybrids or progeny
from our genetic experiments. We
were pretty sure this was our
gene.”
But the researchers needed
more evidence before they could
say that this definitely was the dc
saturase gene they were looking
for. “We next had to follow up
with a biochemical evaluation,”
said Schultz. “That is. we needed
to insert the gene into some type
of living tissue and see if it actual
ly would convert the saturated fat
ty acids to unsaturated fatty acids,
leading to the production of the
sticky material in the resistant ger
aniums.”
The researchers had planned to
insert the gene into plant tissue
and look for the formation of these
fatty acids, a time-consuming stu
dy involving growing the plants to
maturity. But in December 1994,
at a conference in Annapolis, Md.,
Medford met biochemist John
Shanklin, who worked at Brook
haven National Laboratory. “This
was extremely lucky for us, be
cause it just so happened that he
was working with a method of de
saturase gene expression using the
bacterium E. coli,” Medford said.
“Because E. coli very quickly
expresses genes that' are inserted
into it, using this method can con
siderably speed up some genetic
research,” said plant biochemist
Edgar Cahoon, who works in
Shanklin’s lab. “Our research fit
perfectly with the study being
conducted at Penn State.”
Teaming up with Shanklin and
Gaboon enabled the Penn State re
searchers to insert the gene into E.
coli, allowing it to be expressed in
the bacterium and resulting in the
production of two unsaturated fat
ty acids new to the E. coli. The re
searchers then isolated enzymes
from the E. coli and placed them
in contact with various saturated
fatty acid substrates. The interac
tion of the enzymes with the prop
er substrate showed whether the
gene encoded a functional de
saturase and identified the prefer
red substrate.
“We expected the desaturase
encoded by our gene to act on the
saturated fatty acids known as
palmitic (16:0) acid and stearic
(18:0) acid,” said Schultz. “We
discovered that the pathway
actually was more complex. In
stead of desalinating these two
fatty acids, the gene encoded a
protein that acted on a different
fatty acid, known as myrisdc acid
(14:0) and converted it to one
called myristoleic acid (14:1 A’).
This fatty acid was then converted
<&£RtL
Manufacturer of Farm Sprayers
Pressure Washers & Hydraulic Hosas
Matal Fabricating
‘Braka & Shaar Work
Ganaral Welding ft Repair
858 Pumping Station Road Answering Service
Kirkwood, PA 17536 717-529-6553
Gene For Plant Resistance
into the 16:1 A ll and 18:1 A" fatty
acids by the elongation of 14:1A*.
The behavior of the desaturase
was somewhat different from
what we expected, but the out
come showed that we definitely
had identified the desaturase gene
associated with plant resistance. I
see this as the first step in defining
one pathway of pest resistance in
plants at the molecular level.”
Penn State is currently in the
process of patenting the use of this
gene, which could have applica
tions for both agriculture and in
dustry. When more gores that play
a role in this mechanism of plant
resistance are identified, plant
geneticists may be able to transfer
the mechanism to important crops
such as' tomatoes and potatoes.
“These plants are members of the
Solanaceae family, and have simi
lar trichomes,” said Medford.
“Making tomatoes and potatoes
more resistant to certain pests
would be extremely helpful for
growers. In addition, understand
ing the mechanism of pest resis
tance will greatly benefit plant
breeding and integrated pest man
agement programs.”
Another application could
benefit both agriculture and indus
tries that require specialized oils.
“These oils are expensive to
manufacture, but they might be
produced far more cheaply in
Changes
For Angus Herd
COLLEGE PARK, Md. Dr.
Thomas A. Fretz, dean of the Col
lege of Agriculture and Natural
Resources at the University of
Maryland at College Park, has
announced that major changes
will be made to the Wye Angus
beef herd beginning Sept. 1. The
herd is located at the college’s
Wye Research and Education
Center near Queenstown.
The beef herd changes are
designed to ensure full utilization
of the herd for the improvement of
Maryland’s beef industry. They
will be overseen by Dr. Scott Bar
ao, associate professor of animal
sciences, who will assume prog
rammatic responsibility for the
herd.
During the next year.
• The size of the base herd will
be reduced to a level better
matched to the college’s available
resources. The cow herd will be
reconfigured to more closely
reflect the unique germplasm base
developed by Jim Lingle and
gifted to the university by Arthur
Houghton.
• The 1997 Wye Sale will
include a larger than usual offer
ing of select Wye-based females.
Future sales will occur as needed
based on the availability of excess
females or superior genetics that
will benefit Maryland’s cattle
Lancaster Farming, Saturday, August 31,1WM15
plants or in microorganisms,’’ laid
MedfqnL “This could help farm
ers, who could grow crops that
produce these specialty oils.”
‘The faculty at Penn Stale did a
truly admirable job over the years
of combining individuals with
complementary talents and abili
ties in this research program,” said
Andrew Benon, professor emeri
tus of marine biology at Scripps
Institute of Oceanography, Uni
versity of California at San Diego.
‘The result is that Schultz and
others have built on the past re
search and have made a briliant
discovery."
"This is research at its best —it
makes profound contributions to
both basic and applied science.”
said Stuart Patton, Evan Pugh
professor emeritus of agriculture
at Penn State, who informally re
viewed the researchers’ paper.
“This team was highly ingenious
in relating genetics and lipid bio
chemistry to insecticidal proper
,hes of unique fatty acids in ger
aniums.”
“One individual could not have
accomplished this all alone,” said
Schultz. “No one scientist could
have all the skills or knowledge
necessary not to mention there
are decades of research leading up
to the discovery. It was truly a col
laborative effort, and being part of
it was a great learning experi
ence.”
In Store
industry.
• An open Maryland Bull Test
Station will be established at the
Wye REC in 1997. Details con
cerning the test will be made
available this winter.
• An industry advisory commit
tee will be formed to ensure close
communication and collaboration
between the Maryland beef cattle
industry and the university.
The beef cattle research prog
ram conducted at the college’s
Wye Research and Education
Center will focus on addressing
both current and future needs of
the industry.
“We have a unique opportunity
to pursue important beef research
using a forage-based cow/calf pro
duction system with a highly
defined genetic base,” said Barao.
“We will build our efforts around
the concept of integrated resource
management (IRM), and we anti
cipate creating a beef research,
extension and teaching program
that will be highly productive and
responsive to the needs of our
citizens.”
Eddie Draper, along with Dr.
Russell Brinsfield, center head of
the Wye REC, will assist Barao in
these efforts by assuming day-to
day responsibility of the Wye
herd. Draper has worked with the
herd for 10 years and is looking
forward to being a part of a viable
and active research program
BREAKING MILK RECORDS!
Lancaster Farming Carries
DHIA Reports Each Month!