## 1 Introduction
With this in mind, a transcriptomic analysis utilizing Illumina next-generation sequencing has provided an opportunity for identifying novel farnesyl pyrophosphate synthases, terpene synthases, cytochromes P450, and alcohol and aldehyde dehydrogenases that are likely to be involved in the biosynthesis of terpenoids in _Thapsia_. We chose _Thapsia laciniata_. [PERSON] as a representative because of its unique chemical composition, including a diverse variety of oxygenated sesquiterpenoids [4, 6]. The data from this study will be vital for the future biochemical elucidation of the biosynthetic pathways of both regular and irregular terpenoids, such as thapsigargins and thapsanes, respectively. Figure 1: An illustration of the array of enzyme classes that are involved in the diversity of sesquiterpenoids in the Apiaceae. (**A**) Irregular sesquiterpenoids. The genus _Thapsia_ has been subjected to several revisions during the last century. The genus was initially divided into three species: _T. garganica_ L., _T. maxima_ [PERSON] and _T. villosa_ L. [17], with a fourth species, _T. transtagana_ [PERSON], described more recently [18]. At least two other species, _T. minor_ [PERSON] and [PERSON] and _T. laciniata_ [PERSON] 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. Previous studies on the secondary metabolites of the genus _Thapsia_ have shown clear variations between and within the species [6,20]. Only _T. minor_ and _T. laciniata_ contain the irregular terpenoids thapsanes, whereas the other _Thapsia_ species contain highly decorated guaianolides, which are not found in _T. minor_ and _T. laciniata_[6]. Despite the more than 4000 species in the Apiaceae family, nucleotide sequence data has thus far been generated for eight species only (based on publicly available data from NCBI in May 2012). _Daucus carota_ L. (carrot) and the subspecies _sativus_ show 43782 nucleotide and EST entries, and _Apium graveolens_ L. and the variety _dulce_ (celery) return 3528 nucleotide and EST entries that mostly arose from a single study [21]. _Centella asiatica_ (L.[PERSON]. returns 4523 entries, and _Pimpinella brachycarpa_ L., _Angelica sinensis_ L., _Bupleurum chinense_ DC and _B. kaoi_ [PERSON] each have several hundred nucleotide entries publicly available. The complete plastid genome of _D. carota_ was published in 2006 [22], a BAC based library covering approximately 10% of the carrot genome was published in 2009 [23], as well as new transcriptome data in 2012 [24]. Thus, _D. carota_ is currently the most thoroughly sequenced Apiaceae species, and although so far no species within Apiaceae has been fully sequenced and made publicly available, transcriptomes of several species are currently being sequenced, with _D. carota_ and _B. chinense_ being the only ones so far available at the SRA (sequence read archive) at NCBI [25]. Terpenes comprise the largest group of specialized plant metabolites with sesquiterpene lactones being a minor but highly valuable subgroup that are used in a range of industrial and medicinal applications [1]. As mentioned before, studies on the mechanism of biosynthesis of sesquiterpene lactones have so far been limited to the plant family Asteraceae [26, 27, 28], with a single recent study on sesquiterpene synthases from _T. garganica_ that are thought to be the first step in the biosynthesis of thapsigargin [14] and possibly other guaianolides, but not thapsanes. An in-depth knowledge of the genomics of Apiaceae species, of which _T. laciniata_ is a representative, will enable us to expand sesquiterpene lactone research to another plant family. The objective of this study is to discover genes that encode for enzymes involved in the biosynthesis of terpenoids in Apiaceae, with a focus on sesquiterpenoids and lactones thereof, and the description of the related pathways.