New Tobacco, New Crops, New Natural Products; Could the Production of Biofuels Create a New Market n

Source from:  By CHRIS MILAM-Agriculture/Natural Resources Agent for Logan County Septemb 09/24/2008

Although tobacco plants are very productive in terms of their capacity to produce large amounts of leaf and stem material (so-called "biomass") per acre, the relatively high cost of their cultivation via hydroponic greenhouses and transplanting reduces their competitiveness as a direct source of raw feedstock for conversion to biofuels. However, Dr. Ling Yuan at KTRDC sees considerable potential in using the tobacco plant to produce the biological catalysts, called enzymes, that are required in the conversion process. Enzymes are naturally-occurring proteins that are widely used in food processing, detergent products, etc. Their application to digest lignocellulose from corn stalks, switchgrass, and other plant material is a critical step in the conversion of that biomass into the ethanol, butanol, or hydrocarbon mixtures that comprise modern biofuels. Enzymes have traditionally been made by expensive fermentation processes, so a more economical way of producing them is desirable for the biofuels-manufacturing applications. Just as crop plantslike tobacco have been used to produce medicinal proteins such as vaccines, so they can also be engineered to make industrial enzymes, with the attendant advantages of convenient scale-up and attractive economics (particularly at large scale) relative to fermentation. Dr. Yuan's team uses computer-generated structural representations of enzyme molecules to facilitate their design of modifications that will result in new properties. This example displays the essential features of a hemicellulase enzyme whose activity has been broadened to be more useful in biofuels manufacturing. (Enzyme representation created by Josh Werkman, a Ph.D graduate student in Dr. Yuan's laboratory.) Dr. Yuan's research team is introducing the genes for lignocellulose-digesting enzymes into tobacco plants so that the enzymes are sequestered in the leaves. However, there is an additional and unique aspect to their approach which is designed to make the overall economics of plant-based enzyme production even more attractive. This addresses the requirement for several different enzymes in the biomass conversion process, each one being responsible for catalyzing a specific, unique, chemical reaction. Dr. Yuan's team is researching the possibility of broadening the catalytic activity of an individual enzyme to make a single, multi-functional catalyst that could perform all the required functions and be produced in one transgenic tobacco variety. They have already constructed prototypes of this "Jack of all trades" enzyme and expressed them successfully in tobacco leaves. The next stage in this pioneering work will be to assess the effectiveness of these tobacco-made enzymes in the biomass-conversion process. Wild tobacco relative may contribute a strategy for blue-mold resistance The commonly occurring disease of tobacco, blue mold, continues to have a negative impact on tobacco yields in many regions. In the future it may also compromise the optimal production of tobacco for new purposes such as production of the industrial enzymes described in the accompanying story. Consequently, the KTRDC research program maintains a strong interest in seeking new strategies to reduce the effects of blue mold, including the development of resistance in the tobacco plant itself. KTRDC Scientist, Dr. David Zaitlin has discovered that a close relative of the tobacco plant, known botanically as Nicotiana langsdorffii, has evolved a form of resistance that contains the spread of the disease. In his research program at KTRDC he is investigating the genetic basis of this phenomenon, with the ultimate objective of transferring the resistance to commercial tobacco (Nicotiana tabacum) through either conventional breeding or a transgenic strategy. The Nicotiana langsdorffii plant, which is sometimes grown as a garden ornamental, is not immune to blue mold. Rather, the plant restricts the blue-molddamage to just the immediate site of infection, through a process called the "hypersensitive response" (HR). The HR type of resistance has two beneficial effects on the crop as a whole. First, by containing the blue mold to a very small region on the leaf it effectively prevents the disease from spreading throughout the plant and compromising its overall growth and yield. And second, since the invading mold is killed by the HR, the production of infectious spores that would normally spread the disease to other plants does not occur. This breaks the cycle of infection/re-infection that would otherwise result in a disease epidemic. Dr. Zaitlin has determined that a single gene in N. langsdorffii is responsible for this mechanism of blue-mold resistance. With the assistance of colleagues Dr. Shouan Zhang and Mr. J.T. Hall, he has been conducting the detailed characterization of the gene which is a necessary prelude to its eventual isolation (a process called "cloning"). Once the gene is cloned they hope to transfer it into commercial tobacco and into the Nicotiana hybrids that were developed at KTRDC for use with new applications of the crop, such as the production medicinal proteins and industrial enzymes. This project is an example of research that is funded by KTRDC and that would be very difficult, if not impossible, to support through other means such as federal research grants. Leaves of the wild tobacco relative Nicotiana langsdorffii (left) and cultivated tobacco (right) after inoculation with blue-mold spores. The N. langsdorffii HR response keeps the disease contained to the infection sites, as shown by the discrete shape and limited sizes of the damaged (brown) zones. In contrast, a typical blue-mold infection of the cultivated tobacco (Nicotiana tabacum) spreads rapidly through the leaf and is accompanied by chlorosis (yellowing). Enditem