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Doctoral thesis, 2020

The specificities of plant enzymes and their effects on the seed oil quality

Jeppsson, Simon

Abstract

Triacylglycerols, glycerides with three fatty acids, are the chemical constituent of seed oils. The fatty acid composition determines the chemical and physical characteristics of an oil. Conventional vegetable oils contain a few reoccurring fatty acids, but plants can produce several hundreds of different fatty acids. A wide range of plant oils and their fatty acids with specific characteristics are suitable replacements for many fossil-oil based commodities. Plant breeders and researcher are thus, modifying the fatty acid composition in oil crops to enhance such properties. Erucic acid is a fatty acid, with extensive use within industrial applications. Fatty acids originate from the plastids in plants, but the assembly of triacylglycerols occurs in the endoplasmic reticulum, where integral membrane-bound acyltransferases catalyse the formation of triacylglycerols. Modifications of fatty acids occur while they are associated with specific lipid molecules. Different types of fatty acid modifications require association with different lipid molecules, and several unusual fatty acids require multiple sequential modifications. The intricate system of synthesis, modification and assembly thus requires channelling of fatty acids and substrates from different subcellular compartments and concurrent transfer of fatty acids from various lipid molecules, often at multiple occasions. The enzymes governing these processes often have very distinct substrate specificities, which we investigate here. Re-engineering of a seed oil’s fatty acid composition or the introduction of an exotic fatty acid is a complex process and must take into consideration plants endogenous enzymes, their substrate specificities and the available substrate pools. Detailed biochemical characterisations of crucial enzymes are thus essential for a successful outcome of such efforts. We have thoroughly investigated a range of acyltransferases and other enzymes involved in lipid metabolism, mainly focused towards erucic acid in several plant species, including Arabidopsis, Camelina sativa, Brassica napus, Crambe hispanica ssp. abyssinica and Tropaeolum majus. DGAT2 catalyses the acyl-CoA dependent formation of triacylglycerol and is thus one of the acyltransferases involved in oil synthesis. The assessed substrate specificities of several DGAT2 indicate that its substrate specificity is a bottleneck in the further increase of erucic acid. We have also investigated the amino acid sequence motifs governing the specificity towards erucic acid in DGAT2 enzymes.

Keywords

plant lipids; TAG; DGAT; acyltransferase; lipid synthesis; enzyme specificities; erucic acid; oil crop

Published in

Acta Universitatis Agriculturae Sueciae
2020, number: 2020:24
ISBN: 978-91-7760-566-9, eISBN: 978-91-7760-567-6
Publisher: Department of Plant Breeding, Swedish University of Agricultural Sciences

Authors' information

Jeppsson, Simon
Swedish University of Agricultural Sciences, Department of Plant Breeding

UKÄ Subject classification

Genetics and Breeding

URI (permanent link to this page)

https://res.slu.se/id/publ/105274