Functional characterization of wheat ent-kaurene(-like) synthases indicates continuing evolution of labdane-related diterpenoid metabolism in the cereals

Abstract

Wheat (Triticum aestivum) and rice (Oryza sativa) are two of the most agriculturally important cereal crop plants. Rice is known to produce numerous diterpenoid natural products that serve as phytoalexins and/or allelochemicals. Specifically, these are labdane-related diterpenoids, derived from a characteristic labdadienyl/copalyl diphosphate (CPP), whose biosynthetic relationship to gibberellin biosynthesis is evident from the relevant expanded and functionally diverse family of ent-kaurene synthase-like (KSL) genes found in rice (OsKSL). Here we report biochemical characterization of a similarly expansive family of KSL from wheat (the TaKSLs). In particular, beyond ent-kaurene synthases (KS), wheat also contains several biochemically diversified KSLs. These react either with the ent-CPP intermediate common to gibberellin biosynthesis or with the normal stereoisomer of CPP that also is found in wheat (as demonstrated by the accompanying description of wheat CPP synthases). Comparison with a barley (Hordeum vulgare) KS indicates conservation of monocot KS, with early and continued expansion and functional diversification of KSLs in at least the small grain cereals. In addition, some of the TaKSLs that utilize normal CPP also will react with syn-CPP, echoing previous findings with the OsKSL family, with such enzymatic promiscuity/plasticity providing insight into the continuing evolution of diterpenoid metabolism in the cereal crop plant family, as well as more generally, which is discussed here.

Evolution of a Complex Locus for Terpene Biosynthesis in Solanum

“…Indeed, Nt-ABS does not have the deletions in exon 4 and exon 5 that are characteristic of the Solanum TPS-e/f genes (a deletion in exon 4 for TPS18 genes and a deletion in exon 5 for TPS21/ 19/20 genes; Figure 4). The early divergence of this part of the TPS-e/f clade for specialized diterpene biosynthesis (for a similar conclusion, see Sallaud et al, 2012) is in contrast with the situation where TPS-e/f genes for specialized diterpene synthesis evolved from KS more recently within the monocot lineage (Zhou et al, 2012).…”

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

“…Notably, ZmAN2 does not cluster with any class I diTPSs in the maize genome, illustrating a different genomic organization of diterpenoid metabolism in maize as compared with rice and tomato (Solanum lycopersicum), where several specialized diterpenoid pathways form functional biosynthetic clusters (Matsuba et al, 2013;Nützmann et al, 2016). However, the presence of the uncharacterized class II diTPSs ZmCPS3 and ZmCPS4 suggests that specialized diterpenoid metabolism in maize likely follows the common modular blueprint of combining different diTPS and P450 enzymes, as shown for rice, wheat, and various other species across the plant kingdom (Xu et al, 2007a;Zhou et al, 2012;Hall et al, 2013;Cui et al, 2015;Zerbe and Bohlmann, 2015). This hypothesis is substantiated by (1) the in vitro substrate promiscuity of ZmKSL4 with CPP of ent-, syn-, and (+)-stereochemistry and (2) Figure 7.…”

“…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.…”

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].…”