Oliver Yu

Dr. Yu got his B. Sc. from Department of Biophysics at the Fudan University in Shanghai, China, and Ph. D. from Department of Biology at the University of South Carolina, Columbia, SC. He did his postdoctoral training at the DuPont Company in Wilmington, Delaware. He joined the Donald Danforth Plant Science Center in 2001, serving as an Assistant Member, and later an Associate Member and Principal Investigator. He is currently an adjunct professor at the Department of Biology, Washington University in St Louis, and the Division of Plant Sciences at University of Missouri-Columbia.

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Research

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.



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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