Submitted to: Phytochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/7/2006
Publication Date: 6/15/2006
Citation: Dacosta, B.M., Keasling, J.D., Mcmahan, C.M., Cornish, K. 2006. Magnesium Ion Regulation of In Vitro Rubber Biosynthesis by Parthenium Argentatum Gray. Phytochemistry. 67: 1621-1628. Interpretive Summary: Molecular approaches appear to offer the most promise for making substantial improvements in rubber yield and quality in alternative rubber-producing plant species suitable for cultivation in temperate, rather than tropical, regions. P. argentatum lines developed from conventional plant breeding programs are already being produced on a commercial scale. Howvere, a combination of biochemistry-based approaches, and genomics and proteomics methods capitalizing on model systems, promise to generate the fundamental breakthroughs in functional understanding needed to fully exploit molecular methods and generate significantly improved lines. In addition, improvements in tissue culture and transformation methods, especially designed for recalcitrant species, are being aggressively pursued by academic, federal, and industriallaboratories, and their success should greatly facilitate the development and introduction of additional rubber-producing crops, such as sunflower.
Technical Abstract: Natural rubber is produced by a rubber transferase (a cis-preny transferase). Rubber transferase uses allylic pyrophosphate to initiate the rubber molecule and isopentenyl pyrophosphate (IPP) to form the polymer. Rubber biosynthesis also requires a divalent metal cation. Understanding how molecular weight is regulated is important because high molecular weight is required for high quality rubber. We characterized the in vitro effects of Mg2+ on the biosynthetic rate of rubber produced by an alternative natural rubber crop, Parthenium argentatum (guayule). The affinity of the rubber transferase from P. argentatum for IPP'Mg was shown to depend on the Mg2+ concentration in a similar fashion to the H. brasiliensis rubber transferase, although to a less extreme degree. Also, in vitro Mg2+ concentration significantly affects rubber molecular weight of both species, but molecular weight is less sensitive to Mg2+ concentration in P. argentatum than in H. brasiliensis.