Abstract
The C6 aldehydes, alcohols, and the corresponding esters are the most important compounds of virgin olive oil aroma. These C6 volatile compounds are synthesized via the 13-hydroperoxide lyase (13-HPL) branch of the lipoxygenase pathway. In this investigation, a functional analysis of the olive (Olea europaea L.) 13-HPL gene by its overexpression and silencing in olive transgenic lines was carried out. With this aim, sense and RNAi constructs of the olive 13-HPL gene were generated and used for the transformation of embryogenic olive cultures. Leaves from overexpressing lines showed a slight increase in 13-HPL gene expression, whereas RNAi lines exhibited a strong decrease in their transcript levels. Quantification of 13-HPL activity in two overexpressing and two RNAi lines showed a positive correlation with levels of transcripts. Interestingly, RNAi lines showed a high decrease in the content of C6 volatiles linked to a strong increase of C5 volatile compounds, altering the volatile profile in the leaves. In addition, the silencing of the 13-HPL gene severely affected plant growth and development. This investigation demonstrates the role of the 13-HPL gene in the biogenesis of olive volatile compounds and constitutes a functional genomics study in olive related to virgin olive oil quality.
Highlights
Plants produce and emit a huge diversity of volatile organic com pounds, which are released from different tissues such as leaves, fruits, flowers, and roots [1]
Globular somatic embryos were inoculated with the A. tumefaciens strain AGL1 harbouring the binary vectors p35S-olive HPL gene (OeHPL) or pRNAiOeHPL for overexpression or RNAi silencing of the OeHPL gene, respectively
We have studied the effect of overexpressing and silencing the 13-hydroperoxide lyase (13-HPL) gene, which belongs to the LOX pathway, on the volatile composition in olive
Summary
Plants produce and emit a huge diversity of volatile organic com pounds, which are released from different tissues such as leaves, fruits, flowers, and roots [1]. From a chemical point of view, these plant vol atiles are organic lipophilic molecules characterized by low boiling points and high vapor pressures at ambient temperatures. They consti tute a heterogeneous group of compounds that are synthesized from primary metabolites such as carbohydrates, amino acids, and fatty acids [2]. A group of fatty acid-derived plant volatiles of particular relevance are the green leaf volatiles (GLV), which consist of six straight-chain carbons (C6) compounds including aldehydes, alcohols, and esters. The 13-hydroperoxides produced by 13-LOX are subsequently cleaved heterolytically by 13-HPL to C6 aldehydes. C6 aldehydes can undergo reduction by alcohol dehydrogenases (ADH) to form C6 alcohols, which can be esterified with acyl-CoA derivatives in a reaction catalyzed by alcohol acyltransferases (AAT) [2]
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