Publications

• Identification, functional characterization and developmental regulation of sesquiterpene synthases from sunflower capitate glandular trichomes.

  Goepfert J.C., Macnevin G., Ro D.-K., Spring O.

  <h4>Background</h4>Sesquiterpene lactones are characteristic metabolites of Asteraceae (or Compositae) which often display potent bioactivities and are sequestered in specialized organs such as laticifers, resin ducts, and trichomes. For characterization of sunflower sesquiterpene synthases we emp ... >> More

  <h4>Background</h4>Sesquiterpene lactones are characteristic metabolites of Asteraceae (or Compositae) which often display potent bioactivities and are sequestered in specialized organs such as laticifers, resin ducts, and trichomes. For characterization of sunflower sesquiterpene synthases we employed a simple method to isolate pure trichomes from anther appendages which facilitated the identification of these genes and investigation of their enzymatic functions and expression patterns during trichome development.<h4>Results</h4>Glandular trichomes of sunflower (Helianthus annuus L.) were isolated, and their RNA was extracted to investigate the initial steps of sesquiterpene lactone biosynthesis. Reverse transcription-PCR experiments led to the identification of three sesquiterpene synthases. By combination of in vitro and in vivo characterization of sesquiterpene synthase gene products in Escherichia coli and Saccharomyces cerevisiae, respectively, two enzymes were identified as germacrene A synthases, the key enzymes of sesquiterpene lactone biosynthesis. Due to the very low in vitro activity, the third enzyme was expressed in vivo in yeast as a thioredoxin-fusion protein for functional characterization. In in vivo assays, it was identified as a multiproduct enzyme with the volatile sesquiterpene hydrocarbon delta-cadinene as one of the two main products with alpha-muuorlene, beta-caryophyllene, alpha-humulene and alpha-copaene as minor products. The second main compound remained unidentified. For expression studies, glandular trichomes from the anther appendages of sunflower florets were isolated in particular developmental stages from the pre-to the post-secretory phase. All three sesquiterpene synthases were solely upregulated during the biosynthetically active stages of the trichomes. Expression in different aerial plant parts coincided with occurrence and maturity of trichomes. Young roots with root hairs showed expression of the sesquiterpene synthase genes as well.<h4>Conclusion</h4>This study functionally identified sesquiterpene synthase genes predominantly expressed in sunflower trichomes. Evidence for the transcriptional regulation of sesquiterpene synthase genes in trichome cells suggest a potential use for these specialized cells for the identification of further genes involved in the biosynthesis, transport, and regulation of sesquiterpene lactones. << Less

  BMC Plant Biol. 9:86-86(2009) [PubMed] [EuropePMC]

  This publication is cited by 3 other entries.

• Functional characterization of four sesquiterpene synthases from Ricinus communis (castor bean).

  Xie X., Kirby J., Keasling J.D.

  Genome sequence analysis of Ricinus communis has indicated the presence of at least 22 putative terpene synthase (TPS) genes, 13 of which appear to encode sesquiterpene synthases (SeTPSs); however, no SeTPS genes have been isolated from this plant to date. cDNAs were recovered for six SeTPS candid ... >> More

  Genome sequence analysis of Ricinus communis has indicated the presence of at least 22 putative terpene synthase (TPS) genes, 13 of which appear to encode sesquiterpene synthases (SeTPSs); however, no SeTPS genes have been isolated from this plant to date. cDNAs were recovered for six SeTPS candidates, and these were subjected to characterization in vivo and in vitro. The RcSeTPS candidates were expressed in either Escherichia coli or Saccharomyces cerevisiae strains with engineered sesquiterpene biosynthetic pathways, but only two (RcSeTPS1 and RcSeTPS7) produced detectable levels of product. In order to check whether the engineered microbial hosts were adequately engineered for sesquiterpene production, a selection of SeTPS genes was chosen from other plant species and demonstrated consistently high sesquiterpene titers. Activity could be demonstrated in vitro for two of the RcSeTPS candidates (RcSeTPS5 and RcSeTPS10) that were not observed to be functional in our microbial hosts. RcSeTPS1 produced two products, (-)-α-copaene and (+)-δ-cadinene, while RcSeTPS7 produced a single product, (E, E)-α-farnesene. Both RcSeTPS5 and RcSeTPS10 produced multiple sesquiterpenes. << Less

  Phytochemistry 78:20-28(2012) [PubMed] [EuropePMC]

• Two sesquiterpene synthases are responsible for the complex mixture of sesquiterpenes emitted from Arabidopsis flowers.

  Tholl D., Chen F., Petri J., Gershenzon J., Pichersky E.

  Despite the fact that Arabidopsis is largely self-pollinating, its flowers emit a complex mixture of terpene volatiles consisting predominantly of a large group of over 20 sesquiterpenes. Here we report that only two terpene synthases, encoded by the florally expressed genes At5g23960 and At5g4463 ... >> More

  Despite the fact that Arabidopsis is largely self-pollinating, its flowers emit a complex mixture of terpene volatiles consisting predominantly of a large group of over 20 sesquiterpenes. Here we report that only two terpene synthases, encoded by the florally expressed genes At5g23960 and At5g44630, are responsible for the formation of virtually all sesquiterpenes found in the Arabidopsis floral volatile blend. Two independent mutant lines with T-DNA insertions in the previously identified At5g23960 gene lacked the emission of three sesquiterpenes, including the main sesquiterpene volatile (E)-beta-caryophyllene, confirming the previous in vitro functional assignment for this gene. Flowers of a mutant line carrying a T-DNA insertion in gene At5g44630 emitted these three sesquiterpenes, but did not emit any of the remaining sesquiterpene volatiles. An At5g44630 cDNA was expressed in Escherichia coli and the produced protein catalyzed the conversion of farnesyl diphosphate into over 15 sesquiterpenes in similar proportions to those found in the floral volatile blend. At5g23960 and At5g44630 promoter-beta-glucuronidase (GUS) fusion experiments demonstrated that both genes are expressed in several parts of the Arabidopsis flower, with strong At5g23960 promoter-GUS activity in the stigma and strong expression of At5g44630 in intrafloral nectaries. Given the previously reported antimicrobial activity of terpenes, their production in stigmas and nectaries may serve to inhibit microbial infection at these vulnerable sites. A survey of 37 Arabidopsis thaliana ecotypes revealed quantitative, but almost no qualitative, variations of floral monoterpene and sesquiterpene emissions suggesting that floral terpene volatiles must play some significant role in the life of the Arabidopsis plant. << Less

  Plant J. 42:757-771(2005) [PubMed] [EuropePMC]

  This publication is cited by 4 other entries.

• Biosynthesis and emission of terpenoid volatiles from Arabidopsis flowers.

  Chen F., Tholl D., D'Auria J.C., Farooq A., Pichersky E., Gershenzon J.

  Arabidopsis is believed to be mostly self-pollinated, although several lines of genetic and morphological evidence indicate that insect-mediated outcrossing occurs with at least a low frequency in wild populations. Here, we show that Arabidopsis flowers emit both monoterpenes and sesquiterpenes, p ... >> More

  Arabidopsis is believed to be mostly self-pollinated, although several lines of genetic and morphological evidence indicate that insect-mediated outcrossing occurs with at least a low frequency in wild populations. Here, we show that Arabidopsis flowers emit both monoterpenes and sesquiterpenes, potential olfactory cues for pollinating insects. Of the 32 terpene synthase genes in the Arabidopsis genome, 20 were found to be expressed in flowers, 6 of these exclusively or almost exclusively so. Two terpene synthase genes expressed exclusively in the flowers and one terpene synthase gene expressed almost exclusively in the flowers were characterized and found to encode proteins that catalyze the formation of major floral volatiles. A beta-glucuronidase fusion construct with a promoter of one of these genes demonstrated that gene expression was restricted to the sepals, stigmas, anther filaments, and receptacles, reaching a peak when the stigma was receptive to cross pollen. The observation that Arabidopsis flowers synthesize and emit volatiles raises intriguing questions about the reproductive behavior of Arabidopsis in the wild and allows detailed investigations of floral volatile biosynthesis and its regulation to be performed with this model plant system. << Less

  Plant Cell 15:481-494(2003) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• Molecular cloning and characterization of (+)-epi-alpha-bisabolol synthase, catalyzing the first step in the biosynthesis of the natural sweetener, hernandulcin, in Lippia dulcis.

  Attia M., Kim S.U., Ro D.K.

  Hernandulcin, a C15 sesquiterpene ketone, is a natural sweetener isolated from the leaves of Lippia dulcis. It is a promising sugar substitute due to its safety and low caloric potential. However, the biosynthesis of hernandulcin in L. dulcis remains unknown. The first biochemical step of hernandu ... >> More

  Hernandulcin, a C15 sesquiterpene ketone, is a natural sweetener isolated from the leaves of Lippia dulcis. It is a promising sugar substitute due to its safety and low caloric potential. However, the biosynthesis of hernandulcin in L. dulcis remains unknown. The first biochemical step of hernandulcin is the synthesis of (+)-epi-α-bisabolol from farnesyl diphosphate, which is presumed to be catalyzed by a unique sesquiterpene synthase in L. dulcis. In order to decipher hernandulcin biosynthesis, deep transcript sequencings (454 and Illumina) were performed, which facilitated the molecular cloning of five new sesquiterpene synthase cDNAs from L. dulcis. In vivo activity evaluation of these cDNAs in yeast identified them as the sesquiterpene synthases for α-copaene/δ-cadinene, bicyclogermacrene, β-caryophyllene, trans-α-bergamotene, and α-bisabolol. The engineered yeast could synthesize a significant amount (~0.3 mg per mL) of α-bisabolol in shake-flask cultivation. This efficient in vivo production was congruent with the competent kinetic properties of recombinant α-bisabolol synthase (K(m) 4.8 μM and k(cat) 0.04 s(-1)). Detailed chemical analyses of the biosynthesized α-bisabolol confirmed its configuration to be (+)-epi-α-bisabolol, the core skeleton of hernandulcin. These results demonstrated that enzymatic, stereoselective synthesis of (+)-epi-α-bisabolol can be achieved, promising the heterologous production of a natural sweetener, hernandulcin. << Less

  Arch. Biochem. Biophys. 527:37-44(2012) [PubMed] [EuropePMC]

  This publication is cited by 4 other entries.