Tobacco studied as biofuel feedstock

By Anna Austin
Posted January 19, 2010, at 9:43 a.m. CST

Researchers at Thomas Jefferson University's Biotechnology Foundation Laboratories have genetically modified tobacco plant leaves to produce significantly more oil, proving that the plant could serve as biofuel feedstock.

Assistant professor Vyacheslav Andrianov said the research project began in mid-2007, when the University's Biotechnology Foundation director Hilary Koprowski received $1 million through Pennsylvania's Alternative Fuels Incentive Grant Program, to support research of engineering tobacco plants for the production of biodiesel and ethanol.

The researchers believe that tobacco has been largely overlooked as a biofuel resource. "The idea of using tobacco plants as a source of inexpensive biomass was known long before our project started and previous studies of others proved that it can be grown for other needs such as cheap plant protein," Andrianov said. "Other plants like switchgrass or algae were recently suggested as a source of inexpensive biomass for alternative fuel production; however, there are no advantages of these plants over tobacco in terms of oil yield or sugar accumulation. Tobacco is a traditional crop grown all over the country and it will be easy to switch to growing tobacco for biofuel, especially as the demand for smoking tobacco is decreasing because people are trying to live healthier."

Another advantage of growing tobacco for biomass production is that it will not negatively impact food production, Andrianov said. Additionally, tobacco is well-studied genetically, and can be easily modified based. "There are numerous studies known from scientific publications on the pathways of oil biosynthesis in plants and several limiting steps of these pathways were previously identified," Andrianov said. "The idea of our project is to improve some of such limiting factors using genetic modification and to combine improved traits in one plant. Two genes were modified in engineered tobacco plants in our current study."

Diacylglycerol acyltransferase (DGAT) is a key enzyme and a limiting factor in biosynthesis of the triacylglycerol (TAG) class of lipids, the major storage component of plant oil, Andrianov explained. "Overexpression of DGAT constitutively in green leaves changes the balance of oil accumulation like it normally happens in seeds. In our study, we demonstrated 10 to 20 times increase of TAGs accumulation that result in two to three times increase in total oil content in leaves."

In developing seeds, the expression of leafy cotyledon2 (LEC 2), a transcription factor that regulates many other genes and is normally active in storage organs like seeds turning on the process of embryogenesis, results in accumulation of oil in storage oil bodies. "Our idea was to express this gene in a way that we can turn it on in organs where it is normally silent-in leaves, switching the cell developmental program to something imitating embryogenesis and resulting in accumulation of storage compounds including oil accumulation," Andrianov said. "Both genes gave expected results in our hands and the idea is to combine them in one plant that will result in an even greater cumulative effect."

The team plans to continue its research, depending on the availability of funds. "We are going to try modification of other limiting factors like key enzymes of biosynthesis of precursors of fatty acids and combine them with those we have used in our publication," Andrianov said. "We expect that to give us even better results. Also, as biomass for cellulosic ethanol fermentation, tobacco has two main advantages over existing feedstocks-a high amount of easily fermentable sugars, and a low content of lignin, which in other lignocellulitic feedstocks significantly hampers the fermentation process and contributes to high cost."

Recent progress in the optimization of biomass pretreatment methods, the decreasing cost of enzymes and the development of more efficient microbial strains makes the fermentation of optimized tobacco feedstock a very promising option for the production of biofuel ethanol, according to the researchers. "We intend to further optimize tobacco biomass for both ethanol fermentation and biodiesel extraction by overexpressing a combination of genes involved in sugar and lipid metabolism and to study the effects of these combinatorial modifications on both sugar and lipid profiles and plant growth," Andrianov added.

Andrianov's research paper, co-authored by Dr. Nikolai Borisjuk, was published in Plant Biotechnology Journal in December 2009.