The following news release is being issued today by the U.S.
Department of Energy's Brookhaven National Laboratory. An electronic
version of this news release with related images is also available in
online newsroom at:
For release on May 22, 2008, 3:00:00 PM
Important Plant Enzymes Identified
Could be used to improve disease resistance and/or tailor plants for
the production of biofuels or other useful chemical feedstocks
UPTON, NY - Scientists at the U.S. Department of Energy's Brookhaven
National Laboratory have identified enzymes important in the
modification of isoflavonoids, natural plant products that help plants
resist fungal infections, and may have beneficial health effects for
humans as well. The research, which will be published online May 22,
2008, in The Plant Journal, may pave the way for implanting the
isoflavonoid-synthesis pathway into bioenergy crops to promote disease
resistance and thereby prevent yield losses, and/or to enhance the
production of other useful chemical feedstocks.
Using the same approaches described in the journal, the researchers
are now working to identify additional enzymes that play a role in
modifying the structure of plant cell walls. Those enzymes could be
important in changing cell wall digestibility and the production of
biomass suitable for conversion to biofuels.
In nature, isoflavonoids are found mainly in legume plants such as
white clover, soybean, and alfalfa, where they improve disease
resistance and help maintain the symbiotic relationship between the
legumes and microorganisms living in their roots for biomass
production. Some studies also suggest that, when consumed by humans,
these natural plant products may help prevent certain cancers, heart
disease, and menopausal symptoms.
"A lot of people are interested in engineering the isoflavonoid-
synthesis pathway into non-legume plants for the benefit of the plants
and the potential benefits to humans," said Brookhaven biologist Chang-
Jun Liu, lead author on the paper.
This is no small task. For one thing, the isoflavonoid biosynthesis
pathway is complex, with many steps and enzymes taking part. Another
challenge is that accumulating high levels of the intermediate
molecules can be toxic to the plant.
"Legume plants have devised ways to protect themselves by transforming
these intermediates for storage in vacuoles or cell walls," said Liu.
The enzyme that performs that vital transformation is the one Liu
wanted to find.
Liu and his co-authors deduced that the enzyme they were interested in
might possibly belong to a large family of enzymes that perform many
biological functions affecting plant growth, development, disease
resistance, and biosynthesis, as well as cell-wall modification. So
they started their search by looking for genes that might instruct
cells to make proteins in that family.
Fortunately the genes for that protein family share certain common
sequences of genetic information. Using those common sequence
"signatures" as a kind of roadmap, the scientists searched the gene
databases of a model legume plant, looking for genes with similar
signatures. This first screening produced 76 candidate genes that
seemed to belong to the family, including those that might instruct
cells to make the isoflavonoid-producing enzyme.
Based on further bioinformatics analysis and gene-expression tests,
they narrowed the focus to nine candidate genes. They then implanted
those nine genes into strains of E. coli bacteria to produce the
proteins, and tested those proteins' ability to perform the enzyme's
specific function. The scientists found that three enzymes performed
the reaction they were looking for -- transforming intermediates in
the isoflavonoid synthesis pathway into a storable form by adding
short carbon chains, a process called acylation.
The next step was to test those three acylation enzymes in plants. The
scientists added genes for each of the three enzymes to common, non-
legume, laboratory plants that already contained some of the genes for
a partial isoflavone pathway, and tested for the final acylated
"Using these techniques, we were able to confirm at least one enzyme
that actually performed the acylation reaction for isoflavonoids in
planta," Liu said.
In addition to identifying the enzyme, the experiments demonstrated
that the scientists were able to successfully transplant crucial steps
of the isoflavonoid synthesis pathway into a non-legume plant,
bringing the prospect of inserting this pathway into bioenergy crops
closer to reality.
"The enzymes that we found apparently work for the modification of a
range of structurally similar chemicals. They could possibly be used
in the metabolic engineering of value-added chemical feedstocks by,
for example, promoting chemicals' storage in bioenergy crops," Liu
This research was funded by the U.S. Department of Energy's Office of
Biological and Environmental Research within the Office of Science and
by Brookhaven's Laboratory Directed Research and Development program.
In addition to Liu, the research team included Xiao-Hong Yu, a
postdoctoral research associate at Brookhaven Lab, and Min-Huei Chen
of Stony Brook University.
One of ten national laboratories overseen and primarily funded by the
Office of Science of the U.S. Department of Energy (DOE), Brookhaven
National Laboratory conducts research in the physical, biomedical, and
environmental sciences, as well as in energy technologies and national
security. Brookhaven Lab also builds and operates major scientific
facilities available to university, industry and government
researchers. Brookhaven is operated and managed for DOE's Office of
Science by Brookhaven Science Associates, a limited-liability company
founded by the Research Foundation of State University of New York on
behalf of Stony Brook University, the largest academic user of
Laboratory facilities, and Battelle, a nonprofit, applied science and
Visit Brookhaven Lab's electronic newsroom for links, news archives,
graphics, and more: http://www.bnl.gov/newsroom