Transcriptional Regulation of Stearoyl-Acyl Carrier Protein Desaturase Genes in Response to Abiotic Stresses Leads to Changes in the Unsaturated Fatty Acids Composition of Olive Mesocarp.

M Luisa Hernández,M Dolores Sicardo,Miguel Alfonso,José M Martínez-Rivas

doi:10.3389/fpls.2019.00251

Abstract

In higher plants, the stearoyl-acyl carrier protein desaturase (SAD) catalyzes the first desaturation step leading to oleic acid, which can be further desaturated to linoleic and α-linolenic acids. Therefore, SAD plays an essential role in determining the overall content of unsaturated fatty acids (UFA). We have investigated how SAD genes expression and UFA composition are regulated in olive (Olea europaea) mesocarp tissue from Picual and Arbequina cultivars in response to different abiotic stresses. The results showed that olive SAD genes are transcriptionally regulated by temperature, darkness and wounding. The increase in SAD genes expression levels observed in Picual mesocarp exposed to low temperature brought about a modification in the UFA content of microsomal membrane lipids. In addition, darkness caused the down-regulation of SAD genes transcripts, together with a decrease in the UFA content of chloroplast lipids. The differential role of olive SAD genes in the wounding response was also demonstrated. These data point out that different environmental stresses can modify the UFA composition of olive mesocarp through the transcriptional regulation of SAD genes, affecting olive oil quality.

Highlights

Unsaturated fatty acids serve as a major source of reserve energy in the form of triacylglycerols, and constitute complex lipids that are essential components of cellular membranes
We have studied in this work the transcriptional regulation of stearoyl-ACP desaturase (SAD) genes in olive fruit remaining in branches incubated under different abiotic stresses, together with its impact at the metabolite level on the unsaturated fatty acids (UFA) content in different lipid classes of mesocarp tissue from Picual and Arbequina cultivars
While Arbequina SAD transcripts remained practically constant throughout the treatment, in Picual mesocarp the expression levels of the three SAD genes showed a transient and significant increase during the first 3 h of incubation, with SAD1 undergoing a 10-fold increase in gene expression compared to SAD2 and SAD3 with 6- and 3-fold increase, respectively (Figure 1B)

Summary

Introduction

Unsaturated fatty acids serve as a major source of reserve energy in the form of triacylglycerols, and constitute complex lipids that are essential components of cellular membranes. De novo fatty acid biosynthesis starts in the plastid by successive addition of two carbon atoms from acetylCoA, mainly leading to the synthesis of palmitoyl-acyl carrier protein (palmitoyl-ACP) and stearoyl-ACP (Harwood, 2005). These products, which can be desaturated in different cellular compartments, are the source of most of the fatty acids present in plant lipids. The plastidial oleate desaturase (FAD6) and linoleate desaturase (FAD7/8) are located in the plastid, use glycolipids as acyl carriers and NAD(P)H, ferredoxin-NAD(P) reductase and ferredoxin as electron donor system (Supplementary Figure S1)

Methods

Results

Conclusion