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Exploring diterpene metabolism in non‐model species: transcriptome‐enabled discovery and functional characterization of labda‐7,13 E ‐dienyl diphosphate synthase from Grindelia robusta
Author(s) -
Zerbe Philipp,
Rodriguez Selina M.,
Mafu Sibongile,
Chiang Angela,
Sandhu Harpreet K.,
O'NeilJohnson Mark,
Starks Courtney M.,
Bohlmann Jörg
Publication year - 2015
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/tpj.12925
Subject(s) - diterpene , labdane , atp synthase , biochemistry , biology , stereochemistry , biosynthesis , terpenoid , chemistry , enzyme
Summary Grindelia robusta or gumweed, is a medicinal herb of the sunflower family that forms a diverse suite of diterpenoid natural products. Its major constituents, grindelic acid and related grindelane diterpenoids accumulate in a resinous exudate covering the plants’ surfaces, most prominently the unopened composite flower. Recent studies demonstrated potential pharmaceutical applications for grindelic acid and its synthetic derivatives. Mining of the previously published transcriptome of G. robusta flower tissue identified two additional diterpene synthases (di TPS s). We report the in vitro and in vivo functional characterization of an ent ‐kaurene synthase of general metabolism (Gr TPS 4) and a class II di TPS (Gr TPS 2) of specialized metabolism that converts geranylgeranyl diphosphate ( GGPP ) into labda‐7,13 E ‐dienyl diphosphate as verified by nuclear magnetic resonance ( NMR ) analysis. Tissue‐specific transcript abundance of Gr TPS 2 in leaves and flowers accompanied by the presence of an endocyclic 7,13 double bond in labda‐7,13 E ‐dienyl diphosphate suggest that Gr TPS 2 catalyzes the first committed reaction in the biosynthesis of grindelic acid and related grindelane metabolites. With the formation of labda‐7,13 E ‐dienyl diphosphate, Gr TPS 2 adds an additional function to the portfolio of monofunctional class II di TPS s, which catalytically most closely resembles the bifunctional labda‐7,13 E ‐dien‐15‐ol synthase of the lycopod Selaginella moellendorffii . Together with a recently identified functional di TPS pair of G. robusta producing manoyl oxide, Gr TPS 2 lays the biosynthetic foundation of the diverse array of labdane‐related diterpenoids in the genus Grindelia . Knowledge of these natural diterpenoid metabolic pathways paves the way for developing biotechnology approaches toward producing grindelic acid and related bioproducts.