Dynamic evolution of herbivore‐induced sesquiterpene biosynthesis in sorghum and related grass crops

Abstract

). † These two authors contributed equally to this work. SUMMARYSorghum (Sorghum bicolor) plants damaged by insects emit a blend of volatiles, predominantly sesquiterpenes, that are implicated in attracting natural enemies of the attacking insects. To characterize sesquiterpene biosynthesis in sorghum, seven terpene synthase (TPS) genes, SbTPS1 through SbTPS7, were identified based on their evolutionary relatedness to known sesquiterpene synthase genes from maize and rice. While SbTPS6 and SbTPS7 encode truncated proteins, all other TPS genes were determined to encode functional sesquiterpene synthases. Both SbTPS1 and SbTPS2 produced the major products zingiberene, b-bisabolene and b-sesquiphellandrene, but with opposite ratios of zingiberene to b-sesquiphellandrene. SbTPS3 produced (E)-a-bergamotene and (E)-b-farnesene. SbTPS4 formed (E)-b-caryophyllene as the major product. SbTPS5 produced mostly (E)-a-bergamotene and (Z)-c-bisabolene. Based on the genome sequences of sorghum, maize and rice and the sesquiterpene synthase genes they contain, collinearity analysis identified the orthologs of sorghum sesquiterpene synthase genes, except for SbTPS4, in maize and rice. Phylogenetic analysis implied that SbTPS1, SbTPS2 and SbTPS3, which exist as tandem repeats, evolved as a consequence of local gene duplication in a lineage-specific manner. Structural modeling and site-directed mutagenesis experiments revealed that three amino acids in the active site play critical roles in defining product specificity of SbTPS1, SbTPS2, SbTPS3 and their orthologs in maize and rice. The naturally occurring functional variations of sesquiterpene synthases within and between species suggest that multiple mechanisms, including lineagespecific gene duplication, subfunctionalization, neofunctionalization and pseudogenization of duplicated genes, have all played a role in the dynamic evolution of insect-induced sesquiterpene biosynthesis in grasses.

Improved herbivore resistance in cultivated tomato with the sesquiterpene biosynthetic pathway from a wild relative

“…ShZIS belongs to the ent-kaurene Terpene Synthase (TPS)-e/f subfamily (see ref. 19) and is not homologous to other zingiberene synthases, such as sweet basil ObZIS (16), Sorghum SbZIS (SbTPS1) (18), or to other tomato sesquiterpene synthases (19,20). However, both ShZIS and ShSBS are homologous to SlTPS19-20, which belong to an atypical class of monoterpene synthases in S. lycopersicum and Solanum pennellii (Fig.…”

“…Importantly, purified 7-epizingiberene, when applied to the headspace of susceptible cultivated tomato, repelled whiteflies, whereas α-zingiberene isolated from ginger did not (15). Although several zingiberene synthases have been identified (16)(17)(18), including one from S. habrochaites (7), we have now unambiguously identified and characterized 7-epizingiberene synthase from S. habrochaites and modified a cultivated tomato to produce 7-epizingiberene. Moreover, plants with improved herbivore resistance were obtained by traditional breeding and these may contribute to reduced pesticide use.…”

Evolution of a Complex Locus for Terpene Biosynthesis in Solanum

“…However, some areas of plant specialized metabolism have received more attention in this respect. The terpenoid pathway leading to the synthesis of the specialized metabolites of the monoterpene, sesquiterpene, and diterpene classes (with skeletons of 10, 15, and 20 carbons, respectively; Figure 1A) is widespread in plants, and the organization of genes encoding terpene synthases (TPSs; a term designating the enzymes responsible for the synthesis of the basic skeleton structures of mono-, sesqui-, and diterpenes; Figure 1A) has been examined in several plant genomes (Chen et al, 2011;Zhuang et al, 2012). In Arabidopsis, a number of TPS genes are found in close association with other confirmed or putative terpenoid metabolism-related genes, for example, genes encoding geranylgeranyl diphosphate synthases (the enzyme that synthesizes the substrate for diterpene synthases; Figure 1A), cytochrome P450s (which often hydroxylate terpenes), and glycosyl transferases (Aubourg et al, 2002).…”

The α-Terpineol to 1,8-Cineole Cyclization Reaction of Tobacco Terpene Synthases

“…Kampranis et al (2007) altered the 1,8-cineole synthase of Salvia officinalis into an a-terpineol synthase and sesquiterpene synthase. Garms et al (2012) and Zhuang et al (2012) demonstrated that a single amino acid substitution near the active pocket altered the product outcome for the sesquiterpene synthases SbTPS1 and SbTPS2 of Sorghum bicolor. Here, we showed that a single amino acid mutation (F266S), changing the large aromatic side chain of Phe into the small, hydroxylated amino acid Ser, resulted in a significant reduction of the second cyclization reaction in the CIN of N. suaveolens (Fig.…”