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Article|01 Jan 2019|OPEN
Giulio Testone1 , Giovanni Mele1 , Elisabetta di Giacomo1 , Gian Carlo Tenore2 , Maria Gonnella3 , Chiara Nicolodi1 , Giovanna Frugis1 , Maria Adelaide Iannelli1 , Giuseppe Arnesi4 , Alessandro Schiappa4 , Tiziano Biancari4 and Donato Giannino,1 ,
*Corresponding author. E-mail: donato.giannino@ibba.cnr.it

Horticulture Research 6,
Article number: 1 (2019)
doi: 10.1038/hortres.2019.1
Views: 550

Received: 19 Feb 2018
Revised: 19 Jun 2018
Accepted: 20 Jun 2018
Published online: 01 Jan 2019

Abstract

Endives (Cichorium endivia L.) are popular vegetables, diversified into curly/frisée- and smooth/broad-leafed (escaroles) cultivar types (cultigroups), and consumed as fresh and bagged salads. They are rich in sesquiterpene lactones (STL) that exert proven function on bitter taste and human health. The assembly of a reference transcriptome of 77,022 unigenes and RNA-sequencing experiments were carried out to characterize the differences between endives and escaroles at the gene structural and expression levels. A set of 3177 SNPs distinguished smooth from curly cultivars, and an SNP-supported phylogenetic tree separated the cultigroups into two distinct clades, consistently with the botanical varieties of origin (crispum and latifolium, respectively). A pool of 699 genes maintained differential expression pattern (core-DEGs) in pairwise comparisons between curly vs smooth cultivars grown in the same environment. Accurate annotation allowed the identification of 26 genes in the sesquiterpenoid biosynthesis pathway, which included several germacrene A synthase, germacrene A oxidase and costunolide synthase members (GAS/GAO/COS module), required for the synthesis of costunolide, a key precursor of lactucopicrin- and lactucin-like sesquiterpene lactones. The core-DEGs contained a GAS gene (contig83192) that was positively correlated with STL levels and recurrently more expressed in curly than smooth endives, suggesting a cultigroup-specific behavior. The significant positive correlation of GAS/GAO/COS transcription and STL abundance (2.4-fold higher in frisée endives) suggested that sesquiterpenoid pathway control occurs at the transcriptional level. Based on correlation analyses, five transcription factors (MYB, MYB-related and WRKY) were inferred to act on contig83192/GAS and specific STL, suggesting the occurrence of two distinct routes in STL biosynthesis.