Project Number: 5325-41000-043-00
Project Type: Appropriated

Start Date: May 28, 2004
End Date: May 27, 2009

Objective:
In support of the overall objective of developing domestic natural rubber-producing crops, enhanced yields of high quality latex and rubber will be generated in guayule using metabolic engineering. Also, metabolic engineering will be used in attempts to improve sunflower rubber production to commercially-acceptable levels and quality, and to create rubber-producing tobacco. In addition, we will develop effective strategies to reduce or eliminate gene flow from transgenic rubber-producing plants in the greenhouse and field, while using marker-friendly or marker-free methods. Concurrent research will be performed to ensure that the rubber is of commercially acceptable quality, can be used in conventional rubber applications, and that unique properties are identified and profitably exploited in blends, composites and products. Coproducts and agricultural residues from rubber-producing crops will be characterized and profitable uses and products developed.

Approach:
We will purify and sequence subunits of the rubber transferase complex in Parthenium argentatum (guayule) and Hevea brasiliensis, and clone the corresponding genes. Latex and rubber yield in guayule will be enhanced using Agrobacterium tumefaciens-mediated metabolic engineering to optimize substrate synthesis and to over-express the rubber transferase. New lines will be evaluated in field trials. Similar approaches, and ballistic transformation methods, will be used to increase the yield and quality of sunflower rubber, and in attempts to confer rubber biosynthetic ability to tobacco. We also will engineer P. argentatum to make higher molecular weight rubber than currently produced in nature, which may create higher-performance elastomeric materials. Methods to control gene flow will be explored, including development of chloroplast gene expression systems for rubber substrate synthesis to avoid transmittal of new traits in pollen; marker-free and marker-friendly plant transformation techniques to eliminate expression of undesirable genes, like selectable markers for antibiotic resistance, either by eliminating all foreign DNA or by use of environmentally-friendly markers, such as green fluorescent protein and native genes to pigments; male sterility; late flowering; and discovery and manipulation of same-species genes to avoid introduction of foreign genes into the host species. We will determine structural and chemical parameters of enzyme/substrate interactions and evaluate substrate analogs with modified termini and methylene side groups. The chemical properties of novel polymers will be evaluated. We will characterize the unusual cold-temperature properties of P. argentatum latex and attempt to develop elastomeric materials malleable at colder temperatures than currently achievable. Also, characterization of the fundamental properties of latex from different species will reveal differences that impact product manufacture and performance. We will develop a range of rubber products, blends and composites from guayule and sunflower latex, including products with enhanced performance properties for commercial applications in the defense, aerospace and medical industries. We will create new biobased products from the coproducts of rubber-producing crops, including resin, fiber and lignocellulosic bagasse, and evaluate the utility of excess guayule and sunflower lignocellulosic bagasse in biofuel applications. formerly 5325-41000-040-00D (5/04).