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Oliver Yu, Ph.D.
Associate Member and Principal Investigator
Donald Danforth Plant Science Center
975 North Warson Road
Saint Louis, Missouri 63132
314-587-1441 (office)
314-587-1541 (fax)
oyu@danforthcenter.org
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Flavonoids are a
group of ubiquitous and diverse small molecules synthesized by the
phenylpropanoid pathway in higher plants. They have co-evolved with
plants since the beginning of their land colonization millions of
years ago. In legumes, isoflavones are major flavonoid compounds.
Isoflavones may function as phyto-estrogens in animals and play a
major part in health benefits related to soy consumption. In plants,
isoflavones are involved in many plant-microbe interactions. They
are the major defense compounds that inhibit the growth of invading
pathogens and activate programmed cell death in the infected tissue.
Flavonoids and isoflavonoids also serve as signal molecules and
chemo-attractants for symbiotic rhizobia. My lab focuses on the
function and regulation of flavonoid and isoflavonoid biosynthesis.
By silencing the key enzymes in the pathway, we were able to produce
transgenic plants that lack flavonoid and isoflavonoid productions.
These plants showed dramatic phenotypes in disease resistance and
nitrogen fixation. The isoflavone-null soybeans were unable to
develop the nitrogen-fixing root nodules. Biochemical analysis
demonstrated that silencing of isoflavone biosynthesis caused a
redistribution of plant hormone auxin and altered nodule primodia
development. We also discovered that isoflavones can function as
internal nodule signals that direct the rhizobial infection towards
a suitable region inside the roots. In contrast, in Medicago
truncatula, different flavonoids have distinct functions.
Isoflavones in M. truncatula do not affect nodulation. Instead,
flavones and flavonols all contribute to the regulation of nodule
development. We are currently trying to understand the
transcriptional regulation and enzyme interaction mechanisms of
flavonoid biosynthesis. These and other studies of flavones and
isoflavone biosynthesis will help to reveal their roles in
plant-microbe interactions at several different levels. This
information will also facilitate the metabolic engineering of this
important pathway in both soybean and non-legume crops.
The same pathway that produces isoflavones in soybean also produces
resveratrol in grapes. It is another health-promoting poly-phenolic
compound, found mostly in red wines. Studies have suggested that
resveratrol can activate a stress-sensing signal transduction
pathway that eventually leads to increased longevity. We recently
engineered baker yeast to produce resveratrol without fermentation
of grapes. By introducing an engineered bacteria enzyme from
Rhodobacter, and an engineered grape enzyme from Cabernet Franc, we
were able to reconstitute a complete resveratrol biosynthetic
pathway and allow the production of this "red wine compound" without
red wine.
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Figure Legend: Flavonoids play a critical role during nodulation after the
rhizobia have entered the roots. In determinate nodule
producing plants such as soybean, and indeterminate nodule
producing plants such as Medicago truncatula, different
flavonoids have different functions. |
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