A defence-related Olea europaea β-glucosidase hydrolyses and activates oleuropein into a potent protein cross-linking agent

Konstantinos Koudounas, Georgios Banilas, Christos Michaelidis, Catherine Demoliou, Stamatis Rigas, Polydefkis Hatzopoulos

Research output: Contribution to journalArticle

25 Citations (Scopus)

Abstract

Oleuropein, the major secoiridoid compound in olive, is involved in a sophisticated two-component defence system comprising a β-glucosidase enzyme that activates oleuropein into a toxic glutaraldehyde-like structure. Although oleuropein deglycosylation studies have been monitored extensively, an oleuropein β-glucosidase gene has not been characterized as yet. Here, we report the isolation of OeGLU cDNA from olive encoding a β-glucosidase belonging to the defence-related group of terpenoid-specific glucosidases. In planta recombinant protein expression assays showed that OeGLU deglycosylated and activated oleuropein into a strong protein cross-linker. Homology and docking modelling predicted that OeGLU has a characteristic (β/α)8 TIM barrel conformation and a typical construction of a pocket-shaped substrate recognition domain composed of conserved amino acids supporting the β-glucosidase activity and non-conserved residues associated with aglycon specificity. Transcriptional analysis in various olive organs revealed that the gene was developmentally regulated, with its transcript levels coinciding well with the spatiotemporal patterns of oleuropein degradation and aglycon accumulation in drupes. OeGLU upregulation in young organs reflects its prominent role in oleuropein-mediated defence system. High gene expression during drupe maturation implies an additional role in olive secondary metabolism, through the degradation of oleuropein and reutilization of hydrolysis products.

Original languageEnglish
Pages (from-to)2093-2106
Number of pages14
JournalJournal of Experimental Botany
Volume66
Issue number7
DOIs
Publication statusPublished - 1 Apr 2015

Keywords

  • heterologous expression
  • oleuropein
  • olive development
  • plant defence
  • protein cross-linking
  • β-Glucosidase

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