Genomic Organization of Plant Terpene Synthases and Molecular Evolutionary Implications

Abstract

Terpenoids are the largest, most diverse class of plant natural products and they play numerous functional roles in primary metabolism and in ecological interactions. The first committed step in the formation of the various terpenoid classes is the transformation of the prenyl diphosphate precursors, geranyl diphosphate, farnesyl diphosphate, and geranylgeranyl diphosphate, to the parent structures of each type catalyzed by the respective monoterpene (C10), sesquiterpene (C15), and diterpene synthases (C20). Over 30 cDNAs encoding plant terpenoid synthases involved in primary and secondary metabolism have been cloned and characterized. Here we describe the isolation and analysis of six genomic clones encoding terpene synthases of conifers, [(-)-pinene (C10), (-)-limonene (C10), (E)-α-bisabolene (C15), δ-selinene (C15), and abietadiene synthase (C20) from Abies grandis and taxadiene synthase (C20) from Taxus brevifolia], all of which are involved in natural products biosynthesis. Genome organization (intron number, size, placement and phase, and exon size) of these gymnosperm terpene synthases was compared to eight previously characterized angiosperm terpene synthase genes and to six putative terpene synthase genomic sequences from Arabidopsis thaliana. Three distinct classes of terpene synthase genes were discerned, from which assumed patterns of sequential intron loss and the loss of an unusual internal sequence element suggest that the ancestral terpenoid synthase gene resembled a contemporary conifer diterpene synthase gene in containing at least 12 introns and 13 exons of conserved size. A model presented for the evolutionary history of plant terpene synthases suggests that this superfamily of genes responsible for natural products biosynthesis derived from terpene synthase genes involved in primary metabolism by duplication and divergence in structural and functional specialization. This novel molecular evolutionary approach focused on genes of secondary metabolism may have broad implications for the origins of natural products and for plant phylogenetics in general.

Diterpene Resin Acids and Olefins in Calabrian Pine (Pinus nigra subsp. laricio (Poiret) Maire) Oleoresin: GC-MS Profiling of Major Diterpenoids in Different Plant Organs, Molecular Identification and Expression Analysis of Diterpene Synthase Genes

“…In the present work, the isolation of the complete genomic sequences of Calabrian pine DTPSs made it possible to further and complete the analysis of Trapp and Croteau [37] by comparing them with the DTPSs already assigned to class I (Figure 4). Such comparison confirms that, as already noticed among the four DTPSs from Calabrian pine (see above), number, position, and phase of the introns III-XIV are highly conserved in all the class-I DTPS genes, among which AgAS, regarded as descending from a putative ancestral bifunctional DTPS gene (see above).…”

“…According to such classification, the four Calabrian pine DTPS genes isolated in the present study belong to class I, formed mainly by both mono-and bi-DTPS genes containing 12-14 introns, present in both gymnosperms (secondary metabolism) and angiosperms (primary metabolism). Indeed, the aforementioned authors [37] showed a strong conservation of the genomic structure between the genes encoding monofunctional CPS and KS enzymes of angiosperm GA metabolism, on one side, and a gene coding for the bifunctional DTPS abietadiene synthase from Abies grandis (AgAS), involved in specialized metabolism, on the other side. This led the above authors to propose that AgAS might be reminiscent of a putative ancestral bifunctional DTPS from which the monofunctional CPS and KS were derived through gene duplication and the subsequent specialization of each of the duplicated genes for only one of the two ancestral activities.…”

Evolution of Terpene Synthases in Orchidaceae

“…Our analysis showed that no orchid TPSs were grouped in these subfamilies, in accordance with previous conclusions by Chen et.al, and Trapp et.al. [16,62].…”

Molecular and Functional Evolution of the Spermatophyte Sesquiterpene Synthases

“…Evolution in STSs is often the result of intron loss or mutations that lead to subfunctionalization or function loss [38]. For example, a large fragment loss of δ-selinene synthase 2 (Agsel2) from A. grandis was found around intron X that led to Agsel2 being transcribed as a pseudogene [39]. Single amino acid W279A switch converts δ-cadinene synthase (CAD1-A) into germacradien-4-ol synthase [40].…”

“…In this scenario, driven by adaptive evolution, ancestral monoterpene synthases losing the N-terminus signal peptide changed their substrate pool and gradually evolved into STSs. Models for gymnosperm TPS evolution proposed that STSs evolved from diterpene synthases through loss of introns, which resulted in, among other changes, the complete loss of the γ domain [39]. Based on this model, Abies grandis a-bisabolene synthase Ag1 (C6-C1 closure), a three-domain plant STSs, is potentially an intermediate in the evolutionary history from diterpene to sesquiterpene synthase [44].…”