Insights into the Sesquiterpenoid Pathway by Metabolic Profiling and De novo Transcriptome Assembly of Stem-Chicory (Cichorium intybus Cultigroup “Catalogna”)

Giulio Testone,Giuseppe Arnesi,Maria Gonnella,Giovanni Mele,Elisabetta Di Giacomo,Alessandro Schiappa,Gian Carlo Tenore,Giovanna Frugis,Massimiliano Renna,Maria Adelaide Iannelli,Chiara Nicolodi,Donato Giannino

doi:10.3389/fpls.2016.01676

Abstract

Stem-chicory of the “Catalogna” group is a vegetable consumed for bitter-flavored stems. Type and levels of bitter sesquiterpene lactones (STLs) participate in conferring bitterness in vegetables. The content of lactucin—and lactucopocrin-like STLs was higher in “Molfettese” than “Galatina” landrace stalks, regardless of the cultivation sites, consistently with bitterness scores and gustative differences. The “Galatina” transcriptome assembly resulted in 58,872 unigenes, 77% of which were annotated, paving the way to molecular investigation of the STL pathway. Comparative transcriptome analysis allowed the identification of 69,352 SNPs and of 1640 differentially expressed genes that maintained the pattern independently of the site. Enrichment analyses revealed that 4 out of 29 unigenes were up-regulated in “Molfettese” vs “Galatina” within the sesquiterpenoid pathway. The expression of two germacrene A -synthase (GAS) and one -oxidase (GAO) genes of the costunolide branch correlated positively with the contents of lactucin-like molecules, supporting that STL biosynthesis regulation occurs at the transcriptional level. Finally, 46 genes encoding transcription factors (TFs) maintained a differential expression pattern between the two varieties regardless of the growth site; correlation analyses among TFs, GAS, GAO gene expressions and STLs contents suggest that one MYB and one bHLH may act in the pathway.

Highlights

Chicory (Cichorium intybus L.) is cultivated worldwide to produce food, coffee surrogates, forages pharmaceuticals, and healthcare compounds (Street et al, 2013)
The total Sesquiterpene lactones (STL) content was significantly higher in Mol than Gal stems (84.9 ± 5.0 vs. 55.4 ± 3.0 mg kg−1 dry matter) as well as that of total lactucin-like forms (LcTOT, 66.2 ± 6.7 vs. 37.7 ± 4.5) independently of the growth site (Table 1, values in the “Both” line)
Mol stems contained more total STL than those of Gal and differences were ascribed mostly to the genotype diversity and poorly to the environment changes; genotype-environment (GxE) interactions affected the contents of Lc, DHLc, DHdLc, and Lp variation (Table 1 and Table S1)

Summary

Introduction

Chicory (Cichorium intybus L.) is cultivated worldwide to produce food, coffee surrogates, forages pharmaceuticals, and healthcare compounds (Street et al, 2013). Genetic diversity analysis supported the three-cluster structure of C. intybus cultivated germplasm (Kiers et al, 2000; Raulier et al, 2016): witloof, root and leaf chicory groups. The latter embraces “Radicchio,” “Sugarloaf ” and “Catalogna” sub-groups. These latter are appreciated for the bitter and crispy taste They bear a receptacle made of outer whorls of leaves (runcinated-pinnatifid type, large mid-rib) and an inner bulk of inflorescence stems Stem vegetables are novel products moving from a niche to a global market, showing potential use in the minimally or fully processed food chain (Renna et al, 2014)

Methods

Results

Conclusion