It is estimated that more than 500,000 compounds are produced by members of the plant kingdom; however, the process by which plants have developed the ability to make these molecules is not well understood. Compounds known as phenylpropanoids are particularly interesting because they have a wide array of important functions in plants. They serve in the interaction of plants with their environments, mediate certain aspects of plant growth, development and pathogen resistance, and are important structural components of the plant cell wall. For example, in corn phenylpropanoids known as flavonoids are important for plant fertility, and have been suggested to control plant growth. Others are important for plants' resistance to ultraviolet light. Another important example is salicylic acid, a well-known signaling molecule in plant defenses against pathogens. Phenylpropanoids have also been found to play diverse roles in ecology. A host of compounds are given off by flowers to attract pollinating insects. It has also been shown that plants produce compounds that inhibit herbivory and others that inhibit the growth of competing plants. Finally, the phenylpropanoid polymer lignin is necessary for mechanical support and water transport from roots to leaves. Because of its abundance, it is also relevant in an ecological context because it provides an abundant sink for carbon. All of these examples make a compelling argument for improving our understanding of the diversity of phenylpropanoid metabolism and its regulation. This research project focuses on a new pathway of phenylpropanoid metabolism that has recently been discovered in Arabidopsis thaliana. This pathway generates four previously unknown metabolites that are named arabidopyrones. Pyrones are extremely interesting molecules which have been shown to be cytotoxic and can be activated by UV-light to form highly reactive products, suggesting that they may have important biological roles with adaptive significance in the ecology of the organisms that make them. Two of the enzymes that function in this pathway have been discovered and will be characterized in detail as part of this project. One of these belongs to a class of enzymes known as extra-diol ring cleavage dioxygenases. Enzymes of this class can be found in a wide array of plant species, which suggests that they are a widely conserved but poorly explored component of plant metabolism. The ability of these enzymes to cleave catechol-substituted substrates suggests that in addition to being involved in the synthesis of some specialized metabolites, they may have a role in the breakdown of compounds in plants, an area about which virtually nothing is known.
Broader Impacts This project will support the full-time training of two graduate students and several part-time undergraduates. All of these students will be trained in techniques from the fields of biochemistry, genetics, and molecular biology, an interdisciplinary approach that will be essential to their future success. Their strong background in biochemistry will provide them with valuable skills that will allow them to pursue biochemical research in the modern laboratories in the public or private sectors.