Practical applications of cloned insect desaturase genes in crop protection
CALS Impact Statement
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Overview
abstract
Expression of insect desaturase transgenes in yeast cells and plants represents a technological innovation with potential impacts in "green chemistry," i.e., for the production of unsaturated fatty acid precursors of insect pheromones, and in developing insect- and pathogen-resistant crop plants.
United States agriculture depends on technological innovation to increase yield and maintain high qualitity of the food and fiber products that it delivers to United States. and global markets. Synthetic insect sex pheromones are an alternative pest control technology that offers significant environmental, human health, and regulatory advantages over conventional insecticides. However, pheromone-based management approaches face significant technical and economic obstacles that have limited their implementation. In particular, the cost of pheromone production presents a major obstacle to the implementation of pheromone-based control practices for many minor crops systems in the U., where their use might be desirable, due to regulatory issues, or necessary, as a consequence of resistance to insecticides. If pheromones are to play a more prominent role in Integrated Pest Management (IPM) approaches of 21st century U.S. agriculture, it is essential to develop alternative methods to produce them that can be commercialized by small companies that can address the needs of control programs in niche agricultural production systems.
response
I initially proposed an alternative synthetic route to make pheromones from unsaturated fatty acids (UFAs) produced in vivo in cells of the yeast Saccharomyces cerevisiae expressing cloned lepidopteran desaturase genes (Knipple et al., 2000). This idea emerged after we showed that a desaturase-deficient yeast strain genetically transformed with a delta11 desaturase gene cloned from the cabbage looper moth Trichoplusia ni produced a Z11-16 UFA precursor of the T. ni pheromone (Knipple et al., 1998). I chose yeast as an expression system not only because it is a genetic model system, but also because it has very well understood fermentations that are amenable to scale-up, and simple cell recovery and lysis methods permitting extraction and purification of valuable products, such as essential polyunsaturated fatty acids of human and animal nutrition and even complex pharmaceuticals such as hydrocortisone. My group’s development of this approach has resulted in the isolation and functional expression by us and others of dozens of lepidopteran desaturases with distinct enzymatic activities.
impact assessment
The recent synthesis of a biologically active pheromone component from a Z11-16 UFA extracted from transgenic tobacco plants expressing the T. ni delta11 desaturase (Nesnerova et al., 2004) provides proof-of-concept of this technology. Evidence of commercial interest is suggested by a patent application submitted in 2004 by the Cornell Research Foundation and BASF Plant Science LLC, which claims structural and functional properties of another moth desaturase isolated in my lab. An unanticipated use of desaturase transgene technology in crop protection is suggested by our recent finding that tobacco plants expressing the T. ni delta11 desaturase have globally altered fatty acid and lipid compositions in addition to high levels of the fatty acid degradation product cis-3-hexenal associated with resistance to plant pathogens (Hong et al., 2004). Another potential use of this technology in crop protection is suggested by a study of pest-resistant geraniums that were found to have highly fluid leaf glandular trichome exudates containing predominantly unsaturated anacardic acids, which act as a toxic "sticky trap" that deters feeding by aphids and spider mites (Schultz et al., 1996). In contrast, the susceptible geraniums had solid exudates containing predominantly saturated anacardic acids. This resistance phenotype is the result of expression of an unusual delta9 desaturase that produces a Z9-14 UFA, which is elongated via a Z11-16 UFA intermediate to produce unsaturated anacardic acids.
