Strategies to Engineer Plants for Use as Biofuel Feedstocks

There has recently been increasing interest in using genetic engineering or other advanced biological technologies to improve the plants that are used as feedstocks for production of ethanol or other fuels. Some efforts are being directed at food crops like corn: even though most observers today consider corn ethanol to be a transitional fuel, the techniques for genetic engineering of corn are well known and easily practiced, and there are a number of companies that consider corn to be somewhat of a “model crop” and only a short-term product opportunity. Efforts are also ongoing to engineer the plant species that might be alternative biofuel feedstocks , including trees, switchgrass, oil-rich crops like canola or Jatropha and others. The following is an overview of some of the approaches being taken to engineer plants for biofuel use: see Sticklen 2006; Torney et al. 2007; Sticklen 2008; and Weng et al. 2008 for more comprehensive scientific reviews of research in this field. 

Techniques for genetic engineering of plants have been well-established for over two decades, with the earliest methods for transforming dicotyledonous plants being developed in the mid-to-late 1980s and methods for transforming monocots (including most of the world’s important cereal crops) arriving several years later. In many ways, the methodology resembles the techniques used to engineer microorganisms, but with the added challenge of successfully transporting the exogenous DNA through the plants’ cell wall (a feature unique to plants) en route to the cell nucleus. Among the methodologies to accomplish this are the use of Agrobacterium, a microorganism naturally having the ability to inject its DNA into plant cells; electroporation, in which the DNA is transported into plant cells using electric current; and the “gene gun”, where DNA is adhered to extremely small nanospheres which are shot at high velocity into the cells. 

Some of the possible technological approaches to using plant genetic engineering to improve biofuel production are summarized in below. The most common strategies for creating transgenic plants for use as biofuel feedstocks have as their goal the introduction of genetic changes into certain plant species to make them more useful for the production of ethanol and other fuels. For example, one might introduce genes encoding key biodegradative enzymes such as cellulases or ligninases into the plants, to enhance the conversion of cellulose into fermentable sugars, thereby improving the pretreatment of cellulosic feedstocks. Other companies and research groups are focusing on engineering oilseed crops to have altered or enhanced lipid content, to make them more suitable for production of biodiesel (analogous to strategies used for altering algal strains). 

Genetic Engineering Strategies: Plants

  • Overexpress cell-wall hydrolysis enzymes.
    • Cellulases
    • Hemicellulases
    • Ligninases
  • Increase plant biomass, cellulosic biomass.
    • Cellulose biosynthetic enzymes.
  • Lignin modification to reduce need for pretreatment.
    • Down-regulate lignin biosynthesis.
  • Regulated gene expression, so traits are active only when needed.

Another approach is simply to engineer or breed biofuel crop species to grow faster and/or create more biomass.  It has also been proposed that one might engineer plants, particularly trees, to have reduced lignin content, which might greatly facilitate the pretreatment steps now needed to process cellulosic feedstock into fermentable sugars. One intriguing step towards this goal was recently achieved by a group from Brookhaven National Laboratory, who used protein engineering to alter a plant enzyme that catalyzes the synthesis of certain lignin precursors, so that the enzyme instead produced molecules unable to serve as the building blocks for lignin (this engineered enzyme has not yet been tested in plants).  

A number of companies and research groups are taking these genetic engineering approaches one step farther, with the goal of using gene expression promoters capable of being regulated so that key degradative enzymes would not be expressed in the plant tissue until the specific time they are needed.  In this way, transgene expression would remain silent during the normal growth of the plant, but expression would be turned on during pretreatment or processing or at a similar stage when expression of the degradative enzyme is most needed. Companies pursuing this strategy include Agrivida and Farmacule Bioindustries

Finally, there are also several companies that are developing genetically engineered plants as “factories” for the production of enzymes for use in fuel fermentation. Similarly to companies using microorganisms to produce cellulytic or other degradative enzymes, some of these companies (like Medicago) are ones that are already in the business of creating transgenic plants for the commercial production of enzymes or other industrial products, or pharmaceutical products. One such approach is being taken by the seed company Syngenta, which has received approval in several countries (but not the U.S.) to commercially sell a strain of corn that has been engineered to overexpress an amylase enzyme, for use in biofuel production. 

Later entries in this blog will discuss the programs and strategies of commercial biotech companies that are developing modified plant varieties for biofuel use. At this writing, I’m aware of at least 15 companies in the U.S. and elsewhere in the world that are actively pursuing such goals.

D. Glass Associates, Inc. is a consulting company specializing in several fields of biotechnology. David Glass, Ph.D. is a veteran of nearly thirty years in the biotech industry, with expertise in patents, technology licensing, industrial biotechnology regulatory affairs, and market and technology assessments. This blog provides back-up and expanded content to complement a presentation Dr. Glass made at the EUEC 2010 conference on February 2, 2010 entitled “Prospects for the Use of Genetic Engineering in Biofuel Production.” The slides from that presentation are available at www.slideshare.net/djglass99.

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2 thoughts on “Strategies to Engineer Plants for Use as Biofuel Feedstocks

  1. David,

    I assume the Laws and Regulations would significantly reduce risk to the environment. What kind of testing is necessary to determine if naturally occuring plants or algae would be affected when modified plants and enzymes are released? Is this a real concern in your opinion?

    • Jeff, I’ll have a lot more to say about the regulations in later installments of the blog. But you are basically correct that the purpose of the regulations is to assess the potential environmental effect of modified microorganisms or plants that are used industrially or in the open environment. The regulations that apply to microorganisms place a lot of emphasis on “containment” — that is, the adequacy of the fermentation vessels and the industrial processes to minimize or prevent living organisms from being released into the environment. In all cases, whether the plant or microorganism was intended for use outdoors or in an industrial process, the applicant would have to submit information describing the modifications made to the organism, and data assessing its potential effects on the environment or human health. This is usually based on laboratory testing. You ask if I think this is a real concern. In general, I agree that environmental risks should be assessed before certain activities are allowed to take place, and so I think the regulations are appropriate. However, in most cases I feel that the microorganisms, algae and plants that are being modified for improved biofuel production pose very low risks when used in accordance with generally accepted standards and practices, and should therefore not face unusually harsh or lengthy scrutiny under these regulations.

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