Distinct metabolic pathways drive monoterpenoid biosynthesis in a natural population of Pelargonium graveolens. (31st August 2019)

• Record Type: Journal Article
• Authors: Bergman, Matthew E; Chávez, Ángel; Ferrer, Albert; Phillips, Michael A
• Editors: Napier, Richard
• Is Part Of: Journal of experimental botany. Volume 71:Number 1(2020)
• Page Start: 258
• Page End: 271
• Publication Date: 2019-08-31
• Subjects: Essential oils -- Geraniaceae -- glandular trichomes -- isotopic labeling -- monoterpenoid biosynthesis -- untargeted metabolomics -- volatile profiling; Botany -- Periodicals; Botany, Experimental -- Periodicals; Plant physiology -- Periodicals; 580
• DOI: 10.1093/jxb/erz397
• Languages: English
• ISSNs: 0022-0957

Abstract

Abstract: Pelargonium graveolens is a wild predecessor to rose-scented geranium hybrids prized for their essential oils used as fragrances and flavorings. However, little is known about their biosynthesis. Here we present metabolic evidence that at least two distinct monoterpene biosynthetic pathways contribute to their volatile profiles, namely, cyclic p -menthanes such as (−)-isomenthone and acyclic monoterpene alcohols such as geraniol and (−)-citronellol and their derivatives (referred to here as citronelloid monoterpenes). We established their common origin via the 2 C -methyl-d-erythritol-4-phosphate pathway but found no indication these pathways share common intermediates beyond geranyl diphosphate. Untargeted volatile profiling of 22 seed-grown P. graveolens lines demonstrated distinct chemotypes that preferentially accumulate (−)-isomenthone, geraniol, or (−)-citronellol along with approximately 85 minor volatile products. Whole plant 13 CO2 isotopic labeling performed under physiological conditions permitted us to measure the in vivo rates of monoterpenoid accumulation in these lines and quantify differences in metabolic modes between chemotypes. We further determined that p -menthane monoterpenoids in Pelargonium are likely synthesized from (+)-limonene via (+)-piperitone rather than (+)-pulegone. Exploitation of this natural population enabled a detailed dissection of the relative rates of competing p -menthane and citronelloid pathways in this species, providing real time rates of monoterpene accumulation in glandular trichomes. Abstract : Rose-scented geraniums biosynthesize volatiles through distinct cyclic and acyclic monoterpenoid pathways and use (+)-piperitone as an intermediate for p -menthane biosynthesis.