Functional characterization of wheat copalyl diphosphate synthases sheds light on the early evolution of labdane-related diterpenoid metabolism in the cereals

Abstract

Two of the most agriculturally important cereal crop plants are wheat (Triticum aestivum) and rice (Oryza sativa). Rice has been shown to produce a number of diterpenoid natural products as phytoalexins and/or allelochemicals – specifically, labdane-related diterpenoids, whose biosynthesis proceeds via formation of an eponymous labdadienyl/copalyl diphosphate (CPP) intermediate (e.g., the ent-CPP of gibberellin phytohormone biosynthesis). Similar to rice, wheat encodes a number of CPP synthases (CPS), and the three CPS characterized to date (TaCPS1,2,&3) all have been suggested to produce ent-CPP. However, several of the downstream diterpene synthases will only react with CPP intermediate of normal or syn, but not ent, stereochemistry, as described in the accompanying report. Investigation of additional CPS did not resolve this issue, as the only other functional synthase (TaCPS4) also produced ent-CPP. Chiral product characterization of all the TaCPS then revealed that TaCPS2 uniquely produces normal, rather than ent-, CPP; thus, providing a suitable substrate source for the downstream diterpene synthases. Notably, TaCPS2 is most homologous to the similarly stereochemically differentiated syn-CPP synthase from rice (OsCPS4), while the non-inducible TaCPS3 and TaCPS4 cluster with the rice OsCPS1 required for gibberellin phytohormone biosynthesis, as well as with a barley (Hordeum vulgare) CPS (HvCPS1) that also is characterized here as similarly producing ent-CPP. These results suggest that diversification of labdane-related diterpenoid metabolism beyond the ancestral gibberellins occurred early in cereal evolution, and included the type of stereochemical variation demonstrated here.

Discovery, Biosynthesis and Stress-Related Accumulation of Dolabradiene-Derived Defenses in Maize

“…In monocots, diterpenoid pathway networks comprise sets of diTPSs with conserved and species-specific functions in wheat (Triticum aestivum) and rice Xu et al, 2004Xu et al, , 2007aMorrone et al, 2006;Wu et al, 2012;Zhou et al, 2012;Fu et al, 2016). The ensuing diTPS products often undergo further structural modifications through the activity of P450 enzymes, as exemplified in rice by the P450-catalyzed formation of several bioactive diterpenoid metabolites (Swaminathan et al, 2009;Wang et al, 2011Wang et al, , 2012aWang et al, , 2012b.…”

Gene Discovery of Modular Diterpene Metabolism in Nonmodel Systems

“…secondary) metabolism and may have roles in ecological interactions of plants with other organisms. Examples are antimicrobial diterpene phytoalexins in rice (Oryza sativa), wheat (Triticum aestivum), maize (Zea mays), and other cereal crop plants of the family Poaceae (Peters, 2006;Schmelz et al, 2011;Wu et al, 2012;Zhou et al, 2012a); diterpene resin acids of the oleoresin defense of spruce (Picea spp. ), pine (Pinus spp.…”

“…These few include the biosyntheses of taxol in Taxus spp. (Walker and Croteau, 2001;Guerra-Bubb et al, 2012), diterpene resin acids in a few conifers (Hamberger et al, 2011;Keeling et al, 2011a;Zerbe et al, 2012a;Hall et al, 2013), and diterpene defense compounds in rice and wheat (Xu et al, 2007a;Wu et al, 2012;Zhou et al, 2012a). In addition, individual enzymes of specialized diterpene biosynthesis, in particular different diTPS genes, have been functionally characterized in approximately a dozen different species.…”

Signals that stop the rot: Regulation of secondary metabolite defences in cereals

“…Diterpenoid phytoalexins have not yet been reported in wheat despite a full complement of diterpenoid biosynthetic genes [109][110][111]. Instead, this crop relies heavily on phytoanticipins such as BXs for protection against infection [12].…”