NMR carbohydrate content profiles associated to expression analysis and allele polymorphism of inulin genes to assess identity, traceability and value increase of endive cultivars (Cichorium endivia)

Italy is leader in the production of leafy vegetables such as endive and escarole (C. endivia var. latifolium and var. crispum), which are consumed as fresh or minimally processed food. The project CISIA aims at assessing the identity and traceability of some patented varieties. The profiles of carbohydrate content, which included that of the prebiotic inulin, gene transcription and allelic variability were used to fingerprint and valorise cultivars of broad-leafed ('Confiance' and 'Flester', a.k.a. escaroles) and curly-leafed endive ('E02.7162' and 'Myrna') at harvest. Thirty eight hydro-soluble metabolites were profiled by NMR and statistical analyses significantly discriminated the broad- from the curly- leafed genotypes. Concerning carbohydrates, minimal (though significant) differences were observed for sucrose, glucose and fructose among the four cultivars. Most interestingly, the inulin content (g kg-1 dry weight) of the curly-leafed varieties was ca. two fold higher than that of escaroles (11.9± 4.3 vs 6.23±1.4). The expression of major inulin synthesis (fructosyl-fructosyl transferase, FFT; sucrose sucrosyl transferase, SST) and catabolic (Fructan 1-exohydrolases I and II, FEHI and FEHIIa) genes was monitored. The transcription levels of both SST and FFT significantly differed in the four varieties, being maximal in 'Myrna', followed by 'E02.7162', 'Confiance' and 'Flester'. The FEHI transcription did not vary in the four cultivars, whereas the FEHIIa expression was maximal and minimal in 'Confiance' and 'Flester' escaroles, respectively, and was comparable in the two curly-leafed endives. Overall, the mRNA abundance of the two catabolic genes was significantly higher than those of synthesis. Finally, the structural diversity (single nucleotide polymorphism) of the aforesaid inulin genes was studied to discriminate the four genotypes.