(E)-β-Ocimene and Myrcene Synthase Genes of Floral Scent Biosynthesis in Snapdragon: Function and Expression of Three Terpene Synthase Genes of a New Terpene Synthase Subfamily

Abstract

Snapdragon flowers emit two monoterpene olefins, myrcene and ( E )-␤ -ocimene, derived from geranyl diphosphate, in addition to a major phenylpropanoid floral scent component, methylbenzoate. Emission of these monoterpenes is regulated developmentally and follows diurnal rhythms controlled by a circadian clock. Using a functional genomics approach, we have isolated and characterized three closely related cDNAs from a snapdragon petal-specific library that encode two myrcene synthases ( ama1e20 and ama0c15 ) and an ( E )-␤ -ocimene synthase ( ama0a23 ). Although the two myrcene synthases are almost identical (98%), except for the N-terminal 13 amino acids, and are catalytically active, yielding a single monoterpene product, myrcene, only ama0c15 is expressed at a high level in flowers and contributes to floral myrcene emission. ( E )-␤ -Ocimene synthase is highly similar to snapdragon myrcene synthases (92% amino acid identity) and produces predominantly ( E )-␤ -ocimene (97% of total monoterpene olefin product) with small amounts of ( Z )-␤ -ocimene and myrcene. These newly isolated snapdragon monoterpene synthases, together with Arabidopsis AtTPS14 (At1g61680), define a new subfamily of the terpene synthase (TPS) family designated the Tps-g group. Members of this new Tps-g group lack the RRx 8 W motif, which is a characteristic feature of the Tps-d and Tps-b monoterpene synthases, suggesting that the reaction mechanism of Tps-g monoterpene synthase product formation does not proceed via an RR-dependent isomerization of geranyl diphosphate to 3S -linalyl diphosphate, as shown previously for limonene cyclase. Analyses of tissue-specific, developmental, and rhythmic expression of these monoterpene synthase genes in snapdragon flowers revealed coordinated regulation of phenylpropanoid and isoprenoid scent production.

Variation of Herbivore-Induced Volatile Terpenes among Arabidopsis Ecotypes Depends on Allelic Differences and Subcellular Targeting of Two Terpene Synthases, TPS02 and TPS03

“…3C), which is consistent with the formation of (E)-b-ocimene and (E,E)-afarnesene as common constituents of floral volatile blends in plants (Dudareva et al, 2003;Nieuwenhuizen et al, 2009). However, for the TPS03 gene, the strong promoter-GUS activity and transcript abundance in Col-0 flowers (Fig.…”

“…S5). Several other TPSs producing (E)-b-ocimene or (E,E)-a-farnesene or both of these terpenes have been identified previously from gymnosperms (TPS-d; Martin et al, 2004) and in the TPS-a, -b, -f, and -g subfamilies of angiosperms (Dudareva et al, 2003;Arimura et al, 2004;Mercke et al, 2004;Nieuwenhuizen et al, 2009; Supplemental Fig. S5).…”

Studies on Biosynthetic Genes and Enzymes of Isoprenoids Produced by Actinomycetes

“…Besides Abies grandis, dozens of isoprenoid cyclase genes have been cloned from plants such as castor bean [31] Norway spruce [32,33], maize [34ϳ36], pine [37], ginkgo [38], snapdragon [39], grapevine [40], lotus [41], and tobacco [42]; some of these genes were isolated to investigate the relationship between isoprenoid production and their defensive effects against potential herbivores and pathogens at the molecular genetic level. Moreover, it was proved that among putative isoprenoid synthase genes discovered by whole genome sequence analysis and in silico analysis in Arabidopsis thaliana, at least six genes, namely, At3g25810, At1g61680, At4g16740, At2g24210, At3g25820, and At3g25830, encoded monoterpene synthases [43ϳ46].…”

Induced volatiles of Medicago truncatula: molecular diversity and mechanistic aspects of a multiproduct sesquiterpene synthase from M. truncatula

“…[5] Thus, the biosynthesis of the volatiles responds in a highly complex manner to below-ground and above-ground impacts, as well as to the sequence in which microbes or herbivores infect or damage the plant. Terpenoid formation is generally assumed to be regulated at the transcript level of the TPS genes, [6] but the mode of regulation is often very complex [7,8] and needs to be studied individually with respect to the plant and the herbivore. Three putative sesquiterpenoid synthases, TPS1, TPS3 and TPS5, were therefore subcloned into the pHis8-3 expression vector and the recombinant vectors were transformed into Escherichia coli BL21-Codon Plus (DE3).…”