Interplay of phenolic compounds and gene expression in phenylpropanoid and flavonoid pathways during olive (Olea europaea L.) ripening of 'Leccino' cultivar

This study presents a detailed analysis and interplay of the phenolics, relative gene expression and quality parameters during ripening of 'Leccino' olive fruit pulp and skin at seven maturity indexes, in the phenylpropanoid and flavonoid pathways. Tissue-specific gene expression analysis revealed statistically higher expression levels for eight genes in the skin. The only exception was anthocyanidin synthase (ANS), which expression level was statistically higher in the pulp. Our results confirm that the important role in olives of the anthocyanin composition have flavonoid 3 '-hydroxylase (F3 ' H) and flavonoid-3 ',5 '-hydroxylase (F3 ' 5 ' H) in both tissues. The phenolic content was mostly statistically higher in the skin than in the pulp and generally increased in both tissues during ripening. A notable shift in phenolic compounds occurs between maturity index 3 and 4, when the skin of the fruit turns completely purple. Results from this study highlight the intricate dynamics of physiological processes and biochemical mechanisms in the phenylpropanoid and flavonoid pathways in olive fruit. The findings also underscore the relationship between phenolic content, relative gene expression, and quality parameters, particularly in relation to color development during ripening in different olive fruit tissues. Our conclusions can be used by growers to improve the quality of fruit and consequently the quality of olive oil or other final products.