Abstract
Specialized metabolism is an evolutionary answer that fortifies plants against a wide spectrum of (a) biotic challenges. A plethora of diversified compounds can be found in the plant kingdom and often constitute the basis of human pharmacopeia. Olive trees (Olea europaea) produce an unusual type of secoiridoids known as oleosides with promising pharmaceutical activities. Here, we transiently silenced oleuropein β-glucosidase (OeGLU), an enzyme engaged in the biosynthetic pathway of secoiridoids in the olive trees. Reduction of OeGLU transcripts resulted in the absence of both upstream and downstream secoiridoids in planta, revealing a regulatory loop mechanism that bypasses the flux of precursor compounds toward the branch of secoiridoid biosynthesis. Our findings highlight that OeGLU could serve as a molecular target to regulate the bioactive secoiridoids in olive oils.
Highlights
Olive (Olea europaea L., Oleaceae) is an emblematic crop of the Mediterranean Basin and over the last decades, the cultivation has expanded to the Americas, Asia, and Oceania mostly due to the high nutritional value of olive oil
Plant chemical defense is often formed as a dual-partner system composed of glycosylated secondary compounds and dedicated detonating β-glucosidases ensuring that a reactive defensive aglycone is released only after deglycosylation (Morant et al, 2008; Piasecka et al, 2015)
In Oleaceae species, the oleuropein/oleuropein β-glucosidase (OeGLU) system serves as a mighty chemical arsenal against herbivores (Konno et al, 1999) and this enzymatic reaction determines the quality and flavor of olive oil (Romero-Segura et al, 2012; Hachicha Hbaieb et al, 2015; Vitaglione et al, 2015)
Summary
Olive (Olea europaea L., Oleaceae) is an emblematic crop of the Mediterranean Basin and over the last decades, the cultivation has expanded to the Americas, Asia, and Oceania mostly due to the high nutritional value of olive oil. The dominant secoiridoid in olives accumulating up to 14% in young drupes is oleuropein (Amiot et al, 1986), an ester of elenolic acid with 2 -(3 ,4 -dihydroxyphenyl)ethanol (hydroxytyrosol) that exhibits antioxidant, anti-inflammatory, antiproliferative, antimicrobial, and Silencing of Oleuropein β-Glucosidase antiviral activities, being a metabolite of high interest for humans (Bulotta et al, 2013). Deglycosylation of oleuropein by OeGLU produces an unstable aglycone form that is rapidly converted to a highly reactive molecule with a glutaraldehyde-like structure. This compound covalently binds to amino acids and exhibits strong protein denaturing/cross-linking activities, providing a mighty arsenal against herbivores (Konno et al, 1999)
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