ADDRESSING THE BITTER TRAIT IN CHICORY "PUNTARELLE": DEVELOPMENT OF TRANSCRIPTIONAL AND SNP MARKERS WITHIN THE SESQUITERPENE PATHWAY

The Catalogna chicory (Cichorium intybus L., Catalogna group) is an Italian typical vegetable; Molfettese and Galatina are Apulian landraces consumed for their tender stems (turions or "puntarelle"). Bitterness is an important organoleptic trait, which directs both consumer and breeding choices and is linked to the content of sesquiterpene lactones (STLs). Major STLs (lactucin, 8-deoxylactucin, lactucopicrin) and respective dihydro-derivatives (1,3-dihydrolactucin, 11(s),13-dihydro-8-deoxylactucin, 11(s),13-dihydrolactucopicrin) were quantified in turions of the two landraces (HPLC). Regardless of the cultivation sites, the content of 1,3-dihydrolactucin and 11(s),13-dihydro-8-deoxylactucin was significantly higher in Molfettese than Galatina. consistently with the more bitter taste of the former. The Galatina reference transcriptome contained 79,716 unigenes and 75 mapped into the sesquiterpenoid and triterpenoid (S&T) biosynthesis pathway (KEGG). In order to survey gene transcriptional variations and polymorphism data, the RNA-seq of Molfettese and Galatina stem transcriptomes was performed. Over two thousand differentially expressed genes (DEGs) were scored between the two genotypes independently of the cultivation zone. KEGG enrichment analyses revealed that four DEGs were up-regulated in Molfettese compared to Galatina within the S&T biosynthesis map. Specifically, the expression of the germacrene A-synthase and -oxidase genes of the Costulonide (a key STL precursor) branch was directly correlated with the contents of 1,3-dihydrolactucin and 11(s),13-dihydro-8-deoxylactucin. The sequences of these genes showed several polymorphic events (SNPs) between the two genotypes and together with the transcriptional divergences represent potential markers for assisted breeding.