Monolignol oxidoreductases in Arabidopsis thaliana

Lignin is a major product of plants and constitutes one of the most abundant natural polymers on earth. The building blocks for the biosynthesis of lignin are called monolignols. These molecules are produced by plant cells, and, subsequently, are polymerized outside the cell to form the extracellular matrix, thus providing the stability to enable plant growth. However, little is known about the fine-tuning of lignin composition in plants. We have identified a family of enzymes, named monolignol oxidoreductases, that modify the chemical properties of monolignols by oxidation of the alcohol to the aldehyde group. These monolignol oxidoreductases belong to the flavin-dependent family of berberine bridge enzymes, which are involved in a number of important biochemical reactions in plants, such as the breakdown of cell wall components. We hypothesize that monolignol oxidoreductases play a role in controlling the extracellular ratio of monolignols and their corresponding aldehydes, and thus, alter the composition of the extracellular pool of lignin monomers. In our research project, we will focus on the role of these enzymes in the biosynthesis and modification of lignin using a small flowering plant mouse-ear cress (Arabidopsis thaliana), which harbors five genes encoding putative monolignol oxidoreductases. In order to reveal the function of these five enzymes in lignin generation, we will investigate their biochemical properties, determine their activity and localization in the plant and study their effect on the composition of lignin employing state-of-the art techniques. With this approach, we expect to gain insight into the role of monolignol oxidoreductases with regard to the mechanisms that alter the composition of lignin, in particular in a developmental context as well as in response to abiotic and biotic stress factors, such as drought and herbivores. In this sense, our research will not only promote our understanding of plant development and defense strategies, but may also be valuable for efforts to manipulate the composition of lignin for improved applicability of the plant material in the bio-based economy. The multidisciplinary nature of this research project is strongly reflected by the research team led by Prof. Macheroux at the Institute of Biochemistry (Graz University of Technology) and Prof. Werner at the Institute of Biology (University of Graz) and their external partners at the Weizmann Institute of Science (Prof. Aharoni) and the Great Lakes Bioenergy Research Center in Wisconsin (Prof. Ralph).