Olive Polyphenol Oxidase Gene Family

The phenolic compounds containing hydroxytyrosol are the minor components of virgin olive oil (VOO) with the greatest impact on its functional properties and health benefits. Olive breeding for improving the phenolic composition of VOO is strongly dependent on the identification of the key genes determining the biosynthesis of these compounds in the olive fruit and also their transformation during the oil extraction process. In this work, olive polyphenol oxidase (PPO) genes have been identified and fully characterized in order to evaluate their specific role in the metabolism of hydroxytyrosol-derived compounds by combining gene expression analysis and metabolomics data. Four PPO genes have been identified, synthesized, cloned and expressed in Escherichia coli, and the functional identity of the recombinant proteins has been verified using olive phenolic substrates. Among the characterized genes, two stand out: (i) OePPO2 with its diphenolase activity, which is very active in the oxidative degradation of phenols during oil extraction and also seems to be highly involved in the natural defense mechanism in response to biotic stress, and (ii) OePPO3, which codes for a tyrosinase protein, having diphenolase but also monophenolase activity, which catalyzes the hydroxylation of tyrosol to form hydroxytyrosol.

Automated summary

Phenolic compounds containing hydroxytyrosol have a significant impact on the functional properties and health benefits of virgin olive oil. This study identified and characterized olive polyphenol oxidase (PPO) genes to evaluate their role in the metabolism of hydroxytyrosol-derived compounds. Four PPO genes were synthesized, cloned, and expressed in Escherichia coli, and their functional identity was confirmed using olive phenolic substrates. Among these genes, OePPO2 showed strong diphenolase activity in the oxidative degradation of phenols during oil extraction and appeared to play a vital role in the natural defense mechanism against biotic stress, while OePPO3 encoded a tyrosinase protein with both diphenolase and monophenolase activity, catalyzing the hydroxylation of tyrosol to form hydroxytyrosol.