Cytosolic geraniol and citronellol biosynthesis require a Nudix hydrolase in rose‐scented geranium (Pelargonium graveolens)

Abstract

Summary Geraniol, citronellol and their esters are high‐value acyclic monoterpenes used in food technology, perfumery and cosmetics. A major source of these compounds is the essential oil of rose‐scented geraniums of the genus Pelargonium. We provide evidence that their biosynthesis mainly takes place in the cytosol of glandular trichomes via geranyl monophosphate (GP) through the action of a Nudix hydrolase. Protein preparations could convert geranyl diphosphate (GDP) to geraniol in in vitro assays, a process which could be blocked by inorganic phosphatase inhibitors, suggesting a two‐step conversion of GDP to geraniol. Pelargonium graveolens chemotypes enriched in either geraniol or (−)‐citronellol accumulate GP or citronellyl monophosphate (CP), respectively, the presumed precursors to their monoterpenoid end products. Geranyl monophosphate was highly enriched in isolated glandular trichomes of lines producing high amounts of geraniol. In contrast, (−)‐isomenthone‐rich lines are depleted in these prenyl monophosphates and monoterpene alcohols and instead feature high levels of GDP, the precursor to plastidic p‐menthane biosynthesis. A Nudix hydrolase cDNA from Pelargonium glandular trichomes, dubbed PgNdx1, encoded a cytosolic protein capable of hydrolyzing GDP to GP with a KM of about 750 nm but is only weakly active towards farnesyl diphosphate. In citronellol‐rich lines, GDP, GP and CP were detected in nearly equimolar amounts, while citronellyl diphosphate was absent, suggesting that citronellol biosynthesis may proceed by reduction of GP to CP in this species. These findings highlight the cytosol as a compartment that supports monoterpene biosynthesis and expands the roles of Nudix hydrolases in the biosynthesis of plant volatiles.

Nudix hydrolase WvNUDX24 is involved in borneol biosynthesis in Wurfbainia villosa

“…In addition, the content of borneol generated from BP as substrate was considerably higher than that from BPP, indicating potential differences in the phosphatases that hydrolyze BPP and BP. Recent findings have shown that Nudix hydrolase can catalyze the production of GP and FP from GPP and FPP, respectively, in certain plants such as roses and Pelargonium graveolens , which were then hydrolyzed by hydrolases of broad substrate specificity to produce geraniol and farnesol (Bergman et al., 2021; Sun et al., 2020). Therefore, we hypothesize that Nudix hydrolase may also be involved in the biosynthesis of borneol.…”

“…These enzymes primarily hydrolyze primary metabolites including nucleoside diphosphates, nucleoside triphosphates, coenzyme A, NAD(P)H, and capped mRNAs (Yoshimura & Shigeoka, 2015). In recent years, Nudix hydrolases have also been implicated in plant terpenoid metabolism, e.g., catalyzing the hydrolysis of GPP, isopentenyl diphosphate (IPP), dimethylallyl diphosphate (DMAPP), and farnesyl diphosphate (FPP) to generate the corresponding monophosphate products (Bergman et al, 2021;Conart et al, 2023;Henry et al, 2018). Notably, the Nudix hydrolase RhNUDX1 (Rosa 9 hybrida) converts GPP to geranyl phosphate (GP), which is subsequently hydrolyzed to geraniol by a phosphatase (Magnard et al, 2015).…”

Floral scent emission ofEpiphyllum oxypetalum: identification of a novel cytosol-localized geraniol biosynthesis pathway

“…These results suggest a possible new case for monoterpene biosynthesis, in which a cytosolic TPS might utilize MVA-derived GPP for monoterpene production (MVA-TPS case). This MVA-TPS case might be more ubiquitous than the special MVA-NUDX case for geraniol biosynthesis, as a nudix hydrolase capable of hydrolyzing GPP into geraniol was only characterized for rose hybrids and Pelargonium graveolens (Bergman et al ., 2021) so far, while both TPS and MVA pathway are widely distributed in higher plants.…”

From biosynthesis in plants to post-biosynthetic enzymatic conversion. Generation of odor-impact rose oxides from citronellol-rich essential oils

“…Citronellol biosynthesis has been demonstrated to derive from geraniol in Caenorhabditis plicata, (Haiyang Xu et al 2017) and a similar pathway in pelargonium can be suggested in accordance with the characterization of a geraniol synthase in the species (Blerot et al 2018). Nevertheless, this pathway is still under debate (Bergman M et al 2021). Citronellol is not an end-product but undergoes further modifications through esterification or glycosylation to produce several citronellyl esters and citronellol glycosides.…”