Two bi-functional cytochrome P450 CYP72 enzymes from olive (Olea europaea) catalyze the oxidative C-C bond cleavage in the biosynthesis of secoxy-iridoids - flavor and quality determinants in olive oil.

Carlos E Rodríguez‐López,Sarah E O'Connor,Benke Hong,Valentina Passeri,Luciana Baldoni,Konstantinos Koudounas,Yoko Nakamura,Christian Paetz,Fiammetta Alagna,Ornella Calderini

doi:10.1111/nph.16975

Abstract

Olive (Olea europaea) is an important crop in Europe, with high cultural, economic and nutritional significance. Olive oil flavor and quality depend on phenolic secoiridoids, but the biosynthetic pathway of these iridoids remains largely uncharacterized. We discovered two bifunctional cytochrome P450 enzymes, catalyzing the rare oxidative C-C bond cleavage of 7-epi-loganin to produce oleoside methyl ester (OeOMES) and secoxyloganin (OeSXS), both through a ketologanin intermediary. Although these enzymes are homologous to the previously reported Catharanthus roseus secologanin synthase (CrSLS), the substrate and product profiles differ. Biochemical assays provided mechanistic insights into the two-step OeOMES and CrSLS reactions. Model-guided mutations of OeOMES changed the product profile in a predictable manner, revealing insights into the molecular basis for this change in product specificity. Our results suggest that, in contrast to published hypotheses, in planta production of secoxy-iridoids is secologanin-independent. Notably, sequence data of cultivated and wild olives point to a relation between domestication and OeOMES expression. Thus, the discovery of this key biosynthetic gene suggests a link between domestication and secondary metabolism, and could potentially be used as a genetic marker to guide next-generation breeding programs.

Highlights

Olive (Olea europaea L.) is an economically and culturally important crop in Europe
Oleuropein strongly influences the quality of olive products because of its bitterness, which is a desirable trait in olive oil, though table olives must be subjected to a lengthy curing process to degrade this compound (Garrido-Fernández et al, 1997)
Using secologanin synthase (SLS) from C. roseus as a bait for a homology based search, we identified three SLS homologs in olive, and showed that these SLS homologues either catalyze formation of Oleoside Methyl Ester (OeOMES) or secoxyloganin (OeSXS) from 7

Summary

Introduction

Olive (Olea europaea L.) is an economically and culturally important crop in Europe. The. European Union produces two thirds of the global supply of olive oil, and consumes half of it (European Commission, 2020). Along with wine and bread, are an important part of the Mediterranean diet, in the form of both its fermented, pickled fruit and its oil, which has been consumed for millennia. The specialized metabolites of olive fruit and oil have been associated with various health benefits The secoiridoids are the major class of metabolites present in olive fruit, with oleuropein, a phenolic secoiridoid, making up 6-14% of the dry weight of the fruit (Amiot et al, 1986; Ryan et al, 1999). Oleuropein strongly influences the quality of olive products because of its bitterness, which is a desirable trait in olive oil, though table olives must be subjected to a lengthy curing process to degrade this compound

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