Eugenol Synthase Genes in Floral Scent Variation in Gymnadenia Species
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CORE Metadata, citation and similar papers at core.ac.uk Provided by RERO DOC Digital Library Funct Integr Genomics (2014) 14:779–788 DOI 10.1007/s10142-014-0397-9 ORIGINAL PAPER Eugenol synthase genes in floral scent variation in Gymnadenia species Alok K. Gupta & Ines Schauvinhold & Eran Pichersky & Florian P. Schiestl Received: 9 July 2013 /Revised: 7 August 2014 /Accepted: 31 August 2014 /Published online: 20 September 2014 # Springer-Verlag Berlin Heidelberg 2014 Abstract Floral signaling, especially through floral scent, is activity in Escherichia coli. While G. odoratissima and often highly complex, and little is known about the molecular Gymnadenia conopsea enzymes were found to catalyze the mechanisms and evolutionary causes of this complexity. In formation of eugenol only, the Gymnadenia densiflora pro- this study, we focused on the evolution of “floral scent genes” teins synthesize eugenol, as well as a smaller amount of and the associated changes in their functions in three closely isoeugenol. Finally, we showed that the eugenol and related orchid species of the genus Gymnadenia.Wedevel- isoeugenol producing gene copies of G. densiflora are evolu- oped a benchmark repertoire of 2,571 expressed sequence tags tionarily derived from the ancestral genes of the other species (ESTs) in Gymnadenia odoratissima. For the functional char- producing only eugenol. The evolutionary switch from pro- acterization and evolutionary analysis, we focused on eugenol duction of one to two compounds evolved under relaxed synthase, as eugenol is a widespread and important scent purifying selection. In conclusion, our study shows the mo- compound. We obtained complete coding complementary lecular bases of eugenol and isoeugenol production and sug- DNAs (cDNAs) of two copies of putative eugenol synthase gests that an evolutionary transition in a single gene can lead genes in each of the three species. The proteins encoded by to an increased complexity in floral scent emitted by plants. these cDNAs were characterized by expression and testing for Keywords ESTs . Eugenol . Floral scents . Gymnadenia . Electronic supplementary material The online version of this article Isoeugenol Pollination VOC (doi:10.1007/s10142-014-0397-9) contains supplementary material, which is available to authorized users. A. K. Gupta (*) : F. P. Schiestl Introduction Institute of Systematic Botany, University of Zurich, 8008 Zurich, Switzerland Many insect-pollinated plants communicate with their pollina- e-mail: [email protected] tors through a number of floral signals, such as fragrance, A. K. Gupta unique flower shape, and color (Delle-Vedove et al. 2011; Institute of Integrative Biology, Plant Ecological Genetics, ETH Huber et al. 2005; Salzmann et al. 2007; Salzmann and Schiestl Zurich, 8092 Zurich, Switzerland 2007; Schiestl and Glaser 2012; Streinzer et al. 2010;vander Niet et al. 2011a, b; Vereecken and Schiestl 2009). Floral scents I. Schauvinhold : E. Pichersky Department of Molecular, Cellular and Developmental Biology, are among the key signals in many plant-pollinator systems for University of Michigan, Ann Arbor, MI, USA attracting pollinators from both short and long distances (Brodmann et al. 2008; Huber et al. 2005; Majetic et al. I. Schauvinhold 2007;MiyakeandYafuso2003; Negre et al. 2003;Plepys Laboratorio de Cinética y Fotoquímica, Centro de Investigaciones y Transferencia de Sgo. del Estero, Universidad Nacional de Santiago et al. 2002) and play a vital role in the reproductive success del Estero, Santiago del Estero, Argentina of night-flowering plants, wherein visual cues are usually of minor importance for mediating interactions with pollinators Present Address: (Balao et al. 2011; Dötterl and Jürgens 2005;Guptaetal.2012; A. K. Gupta : I. Schauvinhold : E. Pichersky Department of Ecology and Evolution, University of Lausanne, Le Kondo et al. 2006; Wälti et al. 2009). In addition, several Biophore, 1015 Lausanne, Switzerland studies have established that floral volatiles can serve multiple 780 Funct Integr Genomics (2014) 14:779–788 functions, such as attracting pollinators and deterring the nectar had remained elusive until the present study (Chan et al. 2011; thieves simultaneously (Junker and Blüthgen 2010; Fu et al. 2012; Hsiao et al. 2006, 2011;Monteiroetal.2012; Shuttleworth and Johnson 2009; Theis 2006; Theis et al. Pan et al. 2012; Sedeek et al. 2013; Teh et al. 2011). Therefore, 2009). In plant signaling, volatile blends derived from vegeta- to characterize genes involved in floral- and scent-related tive tissues are generally assumed to enhance predator- pathways, we have constructed one standard and one mediated defenses, whereas floral-based chemicals are strictly subtracted complementary DNA (cDNA) library and devel- considered insect attractants (Heil 2008; Pichersky and oped a benchmark EST resource of 2,571 sequences from Gershenzon 2002; Raguso 2008;vanDam2009). Increasing G. odoratissima. The floral scent compounds, eugenol and evidence, however, suggests that floral-specific chemical sub- isoeugenol, which constitute a group of phenylpropene com- stances can also play a central role in guarding the reproductive pounds, are structurally distinguished from each other only by organs from the antagonists (Kessler and Baldwin 2007; the double-bond position of the propene side chain (Koeduka Kessler et al. 2013;Schiestletal.2011). et al. 2006, 2008). These compounds have also received Gymnadenia odoratissima, Gymnadenia conopsea, and historical attention due to their flavoring and antimicrobial Gymnadenia densiflora rarely hybridize despite being sym- properties (Ahmed et al. 2000; Koeduka et al. 2006;Moleyar patrically distributed (Lönn et al. 2006; Schiestl and Schlüter and Narasimham 1992; Sangwan et al. 1990). Enzymes re- 2009; Soliva and Widmer 1999). Therefore, besides sponsible for the synthesis of eugenol, isoeugenol, and related postzygotic isolation barriers, floral scent has been argued to compounds have been functionally characterized in model be one of the most crucial factors to maintain reproductive plants, such as Petunia (Koeduka et al. 2008), Clarkia isolation among these species (Huber et al. 2005; Schiestl and (Koeduka et al. 2006, 2008), Ocimum (Koeduka et al. Schlüter 2009). Although three Gymnadenia species emit 2006), and Anise (Koeduka et al. 2009). All of these studies quantitatively and qualitatively different blends of approxi- confer that eugenol and isoeugenol are catalyzed by two mately 50 volatile compounds to attract different suits of pol- different types of enzyme (Koeduka et al. 2006, 2008). How- linators, eugenol and benzyl acetate are the only two shared ever, there is still a lack of comprehensive knowledge about active compounds among the scent bouquets of these species evolution of such scent producing genes in plants. In this (Huber et al. 2005;Schiestletal.2011). However, in addition to study, with the use of functional genomics and evolutionary these active compounds, other compounds found in blend can approaches, we investigate a G. odoratissima EST resource as also influence plant performance. For example, Schiestl et al. a starting point and further address about eugenol and (2011) uncovered that the key active compounds (e.g., eugenol isoeugenol emission in naturally occurring three Gymnadenia and phenylacetaldehyde) emitted by G. odoratissima are pos- species, and also about the identification, expression, and itively associated with fitness. However, “non-active” com- evolution of the genes underlying their synthesis. pounds, such as (Z)-isoeugenol, limonene, and α-pinene are negatively correlated with fitness, possibly by interaction with blends of active volatile compounds that altogether can reduce Methods pollinator visitations or increase florivores attractiveness. In orchids, most of the previous molecular studies have Plant materials predominantly made progress either in identifying MADS- box genes for flower development (Aceto and Gaudio 2011; G. odoratissima, G. conopsea,andG. densiflora flowers and Mondragón-Palomino and Theißen 2009; Mondragón-Palo- leaves were harvested from natural populations of Ofenpass mino and Theißen 2011; Mondragón-Palomino and Theissen (G. odoratissima), Albulapass (G. conopsea), and Münstertal 2008;Xuetal.2006) or in molecular phylogeny (Bellusci (G. densiflora) in Switzerland. These samples were imme- et al. 2008; Douzery et al. 1999;Indaetal.2012;Mantetal. diately frozen in liquid nitrogen and stored in a −80 °C 2002; Soliva et al. 2001; van der Niet et al. 2011b). Our freezer until subsequent analyses. Total RNA was isolated current knowledge of biosynthetic pathways that produce from these floral and leaf materials using RNeasy mini kit scent compounds in orchids, however, is still in its infancy. (Qiagen AG, Hombrechtikon, Switzerland). The neces- The food rewarding Gymnadenia species emits a large amount sary permits for all collection locations were obtained of different scent compounds, and therefore, it provides an from the Amt für Natur und Umwelt, Chur, Switzerland, excellent model system to understand the evolutionary pro- for the described field studies. cesses underlying striking scent variability and to study the genes responsible for scent biosynthesis. Surprisingly, to date, Standard cDNA library construction nothing is known about the scent biosynthesis in this species. Despite the increasing number of expressed sequence tags Approximately 1–2 mg of poly(A)+ RNA from G. odoratissima (ESTs) and genomic resources for