Stealing the playbook: a Ph.D. student researches the complex plant defense system
When a plant is attacked by a pathogen or pest, it doesn't just sit meekly by. The plant defense system launches into a red alert mode, producing chemicals to ward off the attacker directly, and even indirectly, by producing chemicals that attract natural predators to the given pest. An example of this is when a grape plant prduces antifungal plant phenolics in response to attack by gray mould fungi, or when tobacco and chili pepper plants produce capcidol in response to attack from an oomycete water-mold.
Reza Sohrabi, a Ph.D. student in biological sciences, has been enamored with the complexity of the plant defense system for many years. He is working with Dorothea Tholl, associate professor of biological sciences and an affiliated faculty member with the Fralin Life Science Institute, to examine the role of terpenoids-- organic compounds produced by plants in response to pest and pathogen attack.
"We want to find out how terpenoids are made, and can defend plants," Sohrabi said.
Terpenoids, also called terpenes, are the main ingredients in the essential oils of many types of plants and flowers, and have a strong fragrance. A class of terpenes, known as 'homoterpenes,' are produced and emitted in response to pest attack by a variety of plants, including important crop species such as corn, lima bean, and cotton. Homoterpenes are thought to be involved in the attraction of herbivore's natural enemies, and thereby defend plants indirectly against attacking pests.
While it was long thought that homoterpenes are produced in leaves only, the Tholl research team discovered that they are also produced in roots, Sohrabi said. Furthermore, using the Arabidopsis plant model, the research team found that the compounds are produced by different pathways above ground (leaves) and below ground (roots). A manuscript summarizing this work is under preparation for publication.
"In the below ground system, the same compound is made from a novel pathway and provides a potential direct defensive function against pathogens," Sohrabi said. "Using quantitative trait loci (QTL) analysis, we were able to narrow down candidate genes loci for terpene production. We also used publicly available microarray data sets, in combination with QTL analysis, to make a short list of gene candidates involved in terpene production."
Sohrabi became hooked on plants as an undergraduate student at the University of Tehran, when working on a project that involved screening transgenic sugar beets resistant to viral infections. During his Ph.D. research at Virginia Tech, he became interested in understanding molecular mechanisms of plant defense against microbes via defensive chemicals.
"This line of research is important because studying the mechanisms of how plants defend themselves against pathogens provides a platform for developing cultivars that are more resistant to pathogens," he said.