Chemical profile and biosynthesis of volatile terpenes in Pityopsis ruthii, a rare and endangered flowering plant

Authors: CHEN, XINLU - University Of Tennessee; NOWICKI, MARCIN - University Of Tennessee; Wadl, Phillip; ZHANG, CHI - University Of Tennessee; KOLLNER, TOBIAS - Max Planck Institute Of Chemical Ecology; PAYA-MILANS, MIRIAM - Tennessee University; STATON, MARGARET - Tennessee University; CHEN, FENG - University Of Tennessee; TRIGIANO, ROBERT - University Of Tennessee

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/14/2023
Publication Date: 6/23/2023
Citation: Chen, X., Nowicki, M., Wadl, P.A., Zhang, C., Kollner, T.G., Paya-Milans, M., Staton, M., Chen, F., Trigiano, R.N. 2023. Chemical profile and biosynthesis of volatile terpenes in Pityopsis ruthii, a rare and endangered flowering plant. PLOS ONE. 18:6. https://doi.org/10.1371/journal.pone.0287524.
DOI: https://doi.org/10.1371/journal.pone.0287524

Interpretive Summary: Interpretive Summary: Pityopsis ruthii is an endangered flowering plant that only grows along limited sections of two rivers in Tennessee, U.S. In this study, researchers from the University of Tennessee, the Max Plank Institute for Chemical Ecology in Germany, and a USDA, ARS, U.S. Vegetable Laboratory scientist in Charleston, SC, characterized the secondary metabolism of Pityopsis ruthii. Specifically, the focus was on the largest family of plant secondary metabolites (terpenes). Terpenes have diverse biological functions in plants and have not been characterized for Pityopsis ruthii. The terpene profile was identified from roots, stems, leaves, and flowers using Gas Chromatography-Mass Spectrometry (GC-MS). The concentrations of terpenes in stems and leaves were comparable, and were 40-50 fold higher than that from roots. Flowers were rich in terpenes, which included 4 monoterpenes and 10 sesquiterpenes. These terpenes were emitted from flowers as volatiles with monoterpenes and sesquiterpenes accounting for almost 80% and 19.3% of total emission of terpenes, respectively. To investigate the biosynthesis of floral terpenes, transcriptome data for flowers were produced and analyzed. Genes involved in the terpene biosynthetic pathway were identified and their relative expressions determined. Using this approach, 67 putative terpene synthase (TPS) genes were detected, which in general are critical for terpene biosynthesis Considering the known biological functions of terpenes, the diversity and tissue- or development-specific production of monoterpenes and sesquiterpenes in Pityopsis ruthii contributes to the biology of this rare flowering plant, and hence its adaptation to specific habitat.

Technical Abstract: Technical Abstract: It is critical to gather biological information about rare and endangered plants to incorporate into conservation efforts. The secondary metabolism of Pityopsis ruthii, an endangered flowering plant that only occurs along limited sections of two rivers (Ocoee and Hiwassee) in Tennessee, USA was studied. By comparative profiling of the nonpolar portion of metabolites from various tissues, P. ruthii flowers were rich in terpenes, which included 4 monoterpenes and 10 sesquiterpenes. These terpenes were emitted from flowers as volatiles with monoterpenes and sesquiterpenes accounting for almost 80% and 19.3% of total emission of terpenes, respectively. These findings suggested that floral terpenes play important roles for the biology and adaptation of P. ruthii to its limited range. To investigate the biosynthesis of floral terpenes, transcriptome data for flowers were produced and analyzed. Genes involved in the terpene biosynthetic pathway were identified and their relative expressions determined. Using this approach, 67 putative terpene synthase (TPS) genes were detected, which in general are critical for terpene biosynthesis. Seven full-length TPS genes encoding putative monoterpene and sesquiterpene synthases were cloned and functionally characterized. Three catalyzed the biosynthesis of sesquiterpenes and four catalyzed the biosynthesis of monoterpenes. In conclusion, P. ruthii plants employ multiple TPS genes for the biosynthesis of a mixture of floral monoterpenes and sesquiterpenes, which probably play roles in chemical defense and attracting insect pollinators alike.