Resurrecting deadly carrots: towards a revision ofThapsia(Apiaceae) based on phylogenetic analysis of nrITS sequences and chemical profiles

Abstract

Thapsia is a small genus of herbaceous perennials in Apiaceae. Thapsia occurs around the Mediterranean, extending from the Atlantic coasts of Portugal and Morocco to Crete and other Greek Islands. Thapsia is commonly known as deadly carrot because of its poisonous effects. The resin from Thapsia spp. has been used in traditional medicine and included in European pharmacopoeias, and several species contain biologically important sesquiterpene lactones, such as thapsigargin. Accordingly, Thapsia has for decades been subject to chemical investigations searching for new specialized metabolites with potential as drug leads. However, no generally accepted taxonomic concept of > 40 species and synonyms exists. To address the phylogenetics and circumscription of Thapsia, we present the first molecular phylogenetic hypothesis of Thapsia based on sequences of the nuclear ribosomal internal transcribed spacer (nrITS) region from 50 accessions of Thapsia and representatives of all currently recognized genera in subtribe Daucinae. Phylogenetic analysis using maximum parsimony and Bayesian inference resulted in a well-resolved topology with strong support for inclusion of all the species studied here from Ammodaucus, Distichoselinum, Elaeoselinum, Guillonea and Margotia in Thapsia, in correspondence with previous phylogenetic studies of Apiaceae. Elaeoselinum is not monophyletic. Clades in Thapsia correlate well with previous observations of groupings based on the occurrence of biologically important sesquiterpene lactones, such as thapsigargin and thapsane and derivatives thereof. The result of the phylogenetic analysis necessitates nomenclatural adjustments. Thus, we propose a broader generic concept for Thapsia. Here T. asclepium, T. gummifera and T. tenuifolia are reinstated, new name combinations are made for T. leucotricha, T. scabra and T. thapsioides, and one new species, T. smittii, is established from T. maxima type II.

Optimization of Biochemical Screening Methods for Volatile and Unstable Sesquiterpenoids Using HS-SPME-GC-MS

“…The full-length sequence was obtained from a cDNA library from T. laciniata Rouy (syn. T. villosa [24]) root material that was collected in early June 2008 just west of Cannes, France (GPS 43.540958, 6.816158), as previously described [2]. Forward and reverse primers (Table 1) were designed with USER-overhangs to enable cloning into a USER compatible version of the pEAQ-HT vector.…”

Phylogeny of Apiaceae subtribe Daucinae and the taxonomic delineation of its genera

“…Since Drude's treatment, the circumscription of Laserpitieae has not generally been changed, although its subtribes are no longer recognized and some modifications at the generic level have been introduced (summarized in Table 1). Four laserpitioid genera have been sunk into Thapsia (Weitzel & al., 2014), and Melanoselinum edule (Lowe) Drude is usually recognized in Version of Record TAXON 65 (3) • June 2016: that members of these tribes form a single clade although the relationships among them remained unresolved due to limited sampling. In these analyses, the representatives of Laserpitium grouped with some members of Caucalideae forming a Daucus clade.…”

Transcriptome Analysis of Thapsia laciniata Rouy Provides Insights into Terpenoid Biosynthesis and Diversity in Apiaceae

“…The species studied here, Thapsia laciniata Rouy (according to Weitzel et al [7]), produces sesquiterpenoids based on the irregular thapsane carbon skeleton (Figure 1A), which has so far only been found in Apiaceae species. Thapsane-type sesquiterpenoids are thought to arise from the irregular terpene precursor, sesquilavandulyl diphosphate (SPP) [8], which itself is the product of an irregular farnesyl diphosphate synthase [9] that can perform one head-tail and one head-head fusion of the three IPP units giving rise to SPP.…”

“…and Link and T. laciniata Rouy have also been described [19]. A recent resurrection of the species led to a new and clearer classification [7]. This latest division has been adopted for this report, for which T. laciniata plants harvested in southern France were studied.…”