LETTUCE GENOME-DRIVEN ASSEMBLY OF ENDIVE TRANSCRIPTOME PROVIDE INSIGHTS INTO SUGAR METABOLISM OF CURLY- AND SMOOTH-LEAF CULTIVARS

The Cichorium endivia (L.) species of the Asteraceae family includes curly- and smoothleafed endives that are worldwide consumed as fresh and minimally processed salads, and sugar content and sweetness are crucial for their quality. The genome release of lettuce, a closely related species, supported the assembly of a reference endive transcriptome, which was enhanced for completeness, accuracy and reliability by combining genome-guided and de-novo strategies. The new transcriptome consisted of a comparable number of mRNAs to that of lettuce (48,533 vs 45,158), transcripts had an average length of 1,454bp and a N50 of 1,798bp, ca. 70% of them were full- or nearly full-length, and the 95% of the deduced products were highly similar (E-value 1e-20) to NCBI database proteins. Consequently, it was possible to annotate over 300 and 50 near fulllength genes of sucrose synthesis/catabolism and transport, respectively. In order to identify differentially expressed genes (DEGs) RNAseq analyses was carried out using edible leaves of curly and smooth cultivars (Domari vs Flester) grown in two distinct sites. After assessment of genotype (G), environmental (E) and interaction effects (GxE) on gene expressions, we focused on transcripts that were minimally affected by E as best candidates influencing the traits at the genetic level, and nine DEGS were selected. Moreover, sucrose, kestose and inulin amounts were influenced by G (higher in curly types) and E (higher in growth site 1 than 2), while the GxE effect was significant only for inulin. The nine DEGs included invertases and sucrose:sucrose fructosyltransferase genes of the inulin branch and their expressions significantly correlated with the target sugar content variations supporting their contribution to oligofructans metabolism.