Suppression of guayulin content in transgenic guayule (Parthenium argentatum Gray) resin along the growth cycle

Authors: VEATCH-BLOHM, MAREN, E - Loyola University; TEETOR, VALERIE, E - University Of Arizona; RAY, DENNIS, T - University Of Arizona; SABA, BEENISH - The Ohio State University; Cornish, Katrina

Submitted to: Discover Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/3/2025
Publication Date: 3/20/2025
Citation: Veatch-Blohm, M., Teetor, Valerie, E, Ray, Dennis, T, Saba, Beenish, Cornish, K. 2025. Suppression of guayulin content in transgenic guayule (Parthenium argentatum Gray) resin along the growth cycle. Discover Plants. 2(75). https://doi.org/10.1007/s44372-025-00136-0.
DOI: https://doi.org/10.1007/s44372-025-00136-0

Interpretive Summary: Guayule commercialization requires market entry into low volume, high margin markets. Such markets include medical and consumer products where guayule's allergy-safe latex is the highest performance latex currently available. However, guayule makes many other secondary products and some of these may cause contact irritation or skin allergies. In this report, it was found that overexpression of genes enocoding rubber polymer initiator molecules also surpressed the synthesis of potentially allergenic resin components called guayulins. The deliberate development of guayule lines with low guayulin levels may help keep the concentrations well below potentially sensitizing levels in occupationally exposed workers, especially in situations where they need to handle crude resin extracts.

Technical Abstract: Guayulins A and B, cinnamic and anisic acid esters, respectively, are important components of guayule (Parthenium argentatum Gray) resin. Characterization of resin components (guayulins A and B) were carried out in three contrasting breeding lines of guayule plants, namely AZ-101, AZ-2, and N6-5 transformed with at least one of three different genes (farnesyl pyrophosphate synthase (FPPS), geranylgeranyl pyrophosphate synthase (GGPPS), and a mutated form of GGPPS, hexa-heptaprenyl pyrophosphate synthase (HHPPS)) through Agrobacterium tumafaciens-mediated transformation of leaf discs. The transgenic guayule plants analyzed were shown to have either unaltered or enhanced resin levels. However, when the levels of guayulins were quantified, although concentrations varied throughout the year, both guayulin A and guayulin B were significantly lower than in wild type and empty vector control plants. Guayulin levels were especially low at the end of two years of growth, when the plants were normally harvested. Apart from the first generation transgenics, their subsequent seed generated progeny plants also had low guayulin levels. Overall, overexpression of allylic pyrophosphate synthase genes suppressed the endogenous guayulin levels in transgenic plants and their seed-generated progeny plants. The deliberate development of guayule lines with low guayulin levels may help keep the concentrations well below potentially sensitizing levels in occupationally exposed workers, especially in situations where they need to handle crude resin extracts.