RESEARCH INTEREST

Plant secondary metabolism, gene regulation, and enzymatic interactions related to isoflavonoid biosyntheis in legumes.


RESEARCH

Plant secondary metabolites represent the most diverse and intriguing organic compounds nature offers. They range from the alkaloid atropine that Cleopatra secretly used as a cosmetic for dilating her pupils to the coniine in hemlock that killed the great philosopher Socrates. Secondary metabolites make petals colorful, flowers aromatic, rubber resilient, and cigarettes addictive. My lab will be focused on one group of secondary metabolites, the isoflavonoids.

Isoflavonoids are aromatic compounds produced predominately in legumes. They play a key role in plant-microbe interactions, serving as the signal molecule for establishing the symbiotic relationship between plants and rhizobial bacteria that results in the formation of nitrogen-fixing root nodules. Isoflavones are also the precursors to the major phytoalexins in legumes. Thus, the activation of isoflavonoid synthesis during the disease-resistance response provides a battery of defense compounds. Isoflavones have drawn much attention recently because of their putative health benefits for humans. Acting as phytoestrogens, isoflavones reportedly relieve menopausal symptoms, reduce osteoporosis, improve blood cholesterol levels, and lower the risk of hormone-related cancers and coronary heart disease.

Isoflavones are synthesized as part of the phenylpropanoid pathway. This pathway has multiple branches that lead to numerous secondary metabolites including lignins, flavanols, anthocyanins, and some phytoalexins. The key enzyme that initiates isoflavonoid synthesis from the general phenylpropanoid pathway is a legume-specific isoflavone synthase (IFS). We have recently cloned this gene, a P450 monooxygenase, from a variety of legumes. Heterologous expression of IFS in both monocot and dicot demonstrated that introduction of IFS alone could result in the novel production of isoflavones in non-legume plants. However, we discovered that isoflavones were produced only in tissues where the phenylpropanoid pathway activity was elevated, such as in floral tissues, UV-treated tissues, and tissues where foreign expression of a transcription factor specifically turned on the phenylpropanoid pathway.

My lab at the Danforth Center focuses on the enzymatic interactions between the key enzymes in the phenylpropanoid and isoflavonoid pathways and the transcriptional regulation of isoflavonoid synthesis. Specifically, we study the mode of action of the six key enzymes involved in the synthesis of flavonoids and isoflavonoids. We attempt to demonstrate metabolic channeling among the multienzyme complexes in the phenylpropanoid and isoflavonoid pathways and to reveal its mechanisms. Proposed genetic engineering of legumes and non-legume plants can alter the production of these secondary metabolites and lead to the synthesis of novel isoflavonoid compounds with significant human health benefits. We also study the transcriptional regulation of these two pathways, focusing on the Myb-like transcription factors that activate gene expression during plant defense and plant-Rhizobium interactions. By investigating the transcription factor-promoter interactions and the signal transduction pathways, the mechanisms that control the production of these important phytoalexins and Rhizobial chemo-attractants can be discovered.


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