INSIGHTS INTO MOLECULAR ROUTES LEADING TO GABA ACCUMULATION IN PACKAGED BROCCOLI-RAAB/"CIME DI RAPA"

Broccoli-raab, known as "cime di rapa"/"friarielli", belong to Brassica rapa susp. sylvestris (L.) Jansch; they are shoots made of leaves, stem a florets, eaten as cooked vegs, and have traditional and economic relevance in south-central Italy. Seed multiplication is still based on pollinated landraces and the packaged product has expanded in large scale retailing. Florets are most appreciated if closed (stay-green), pungent taste, and healthy for nutrtitional composition. In a context of valorisation of organic local product and shelf-life performance (supported by the Project TOC - "Gruppi di Ricerca" by Regione Lazio and Enza Zaden), metabolic and transcriptomic variations were addressed in two genotyp (unregistered hybrid and a market spread "novantino") by comparing field- harvested (FH, control) against stored fresh (SF) and stored pack florets (SP). Overall, 28 hydrosoluble compounds were quantifie untargeted NMR approach (amino acids, carbohydrates, organic vitamins, quercetin, others) and principal component analysis n pictured the variables that distinguished FH, SF and SP florets, while it was less effective in genotype separation. Interestingly, aminobutyric acid (GABA), a non-protein amino acid of health importance was over 30-fold accumulated in bagged florets compared to the fi harvested ones. Parallel RNA-seq analyses showed that both genotypes ha over 4000 differentially expressed genes in SF vs FH that raised up to over 8000 in SP vs FH. Focusing on SP vs FH florets, weighted gene expressio correlation analysis allowed the selection of modules significantly linked to GABA variations and pointed at candidate genes underpinning regulation. After constructing the GABA pathways (synthesis, catabolism and transport), its accumulation in packaged florets of both genotypes could be significantly correlated to the reduced expression ofGABA-transaminase, which is responsible for GABA degradation. A modest repression/unvari transcription of glutamate decarboxylase (GAD) - encoding the enzyme of GABA direct synthesis from glutamate - was also observed, suggesting it minor contribution to GABA accumulation in the four-day SP florets. Thi indicates that GAD up-regulation could have occurred at earlier stag (e.g. during washing, drying, and bagging).