Overexpression of tocopherol biosynthesis genes in guayule (Parthenium argentatum) reduces rubber, resin and argentatins content in stem and leaf tissues

Authors: Ponciano, Grisel; Dong, Niu; Dong, Chen; Breksa, Andrew; Vilches, Ana; ABUTOKAIKAH, MAHA - New Mexico State University; McMahan, Colleen; HOLGUIN, F - New Mexico State University

Submitted to: Phytochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/9/2024
Publication Date: 3/22/2024
Citation: Ponciano, G.P., Dong, N., Dong, C., Breksa Iii, A.P., Vilches, A.M., Abutokaikah, M.T., McMahan, C.M., Holguin, F.O. 2024. Overexpression of tocopherol biosynthesis genes in guayule (Parthenium argentatum) reduces rubber, resin and argentatins content in stem and leaf tissues. Phytochemistry. 222:114060. https://doi.org/10.1016/j.phytochem.2024.114060.
DOI: https://doi.org/10.1016/j.phytochem.2024.114060

Interpretive Summary: Natural rubber produced in stems of guayule (Parthenium argentatum) is susceptible to post-harvest degradation from microbial or thermo-oxidative processes, especially once stems are chipped. Moreover, rubber extraction from guayule requires addition of antioxidants to prevent oxidative degradation of the rubber. These antioxidants may have negative impacts on human health and to the environment. Increasing in vivo guayule natural antioxidants, such as tocopherols, could protect rubber from degradation during post-harvest and the extraction process. We developed transgenic guayule lines with enhanced tocopherol content and one line showed a slight protective effect on post-harvest rubber degradation. Interestingly, the enhanced tocopherol biosynthesis resulted in a disruption of the isoprenoid pathways that synthesize rubber, resin, and the triterpenoids argentatins resulting in their significantly lower contents in the transgenic lines.

Technical Abstract: Natural rubber produced in stems of the guayule plant (Parthenium argentatum) is susceptible to post-harvest degradation from microbial or thermo-oxidative processes, especially once stems are chipped. As a result, the time from harvest to extraction must be minimized to recover high quality rubber, especially in warm summer months. Tocopherols are natural antioxidants produced in plants through the shikimate and methyl-erythtiol-4-phosphate (MEP) pathways. We hypothesized that increased in vivo guayule tocopherol content might protect rubber from post-harvest degradation, and/or allow reduced use of chemical antioxidants during the extraction process. With the objective of enhancing tocopherol content in guayule, we overexpressed four Arabidopsis thaliana tocopherol pathway genes in AZ-2 guayule via Agrobacterium-mediated transformation. Tocopherol content was increased in leaf and stem tissues of most transgenic lines, and some improvement in thermo-oxidative stability was observed. Overexpression of the four tocopherol biosynthesis enzymes, however, altered other isoprenoid pathways resulting in reduced rubber, resin and argentatins content in guayule stems. The latter molecules are mainly synthesized from precursors derived from the mevalonate (MVA) pathway. Our results suggest the existence of crosstalk between the MEP and MVA pathways in guayule and the possibility that carbon metabolism through the MEP pathway impacts rubber biosynthesis.