Development of a Sunflower Crop for Large Scale Production of Natural Rubber

Natural rubber is an essential manufacturing material that possesses performance properties that are superior to synthetic rubber for many product applications, including increased tear and tensile strength, as well as superior mechanical performance properties. Aircraft tires, for example, are made of natural rubber; whereas, synthetic rubber (which is less expensive to procure) is used for less demanding products. Some military grade rubber products, machinery, and equipment are in line with natural rubber’s properties having unique specifications for operation and remaining functional in unique conditions (e.g., high impact of an aircraft landing, shock of an inordinately heavy/large vehicle driving in rough terrain). However, natural rubber production is limited to a single species (rubber tree) in a limited geographic area (Southeast Asia), concentrations that have enabled leaf fungus to spread in rubber plantations in Southeast Asia and negatively impact NR production. Producing rubber from another commercial crop such as sunflower would greatly reduce the probability of a disruption in its supply and potentially make the US independent of imported natural rubber. Sunflower currently accumulates rubber in its leaves at 1-2% dry weight. For sunflower to become a commercially viable source of rubber, this level must be increased 3- to 5-fold. The overall goal of this STTR project is to engineer sunflower with higher levels of rubber production enabling a commercially competitive, domestically and sustainably sourced, rubber crop. Phase I characterized the role of three potentially key genes in rubber biosynthesis. Phase II has two objectives. Objective 1 is to perform field trials to further evaluate transgenic lines identified in Phase I with higher levels of rubber accumulation and/or the production of a rubber polymer with higher molecular weight. Objective 2 will generate additional transgenic lines that represent a step improvement in rubber accumulation over Phase I transformed lines co-expressing a heterologous isoprenoid pathway gene in combination with two different heterologous rubber pathway genes. The Phase II option has the objective of optimizing rubber extraction technology for the improved sunflower leaves.