Modified oleic cottonseeds show altered content, composition and tissue-specific distribution of triacylglycerol molecular species

Abstract

Targeted increases in monounsaturated (oleic acid) fatty acid content of refined cottonseed oil could support improved human nutrition and cardiovascular health. Genetic modifications of cottonseed fatty acid composition have been accomplished using several different molecular strategies. Modification of oleic acid content in cottonseed embryos using a dominant-negative protein approach, while successful in effecting change in the desired fatty acid composition, resulted in reduced oil content and seed viability. Here these changes in fatty acid composition were associated with changes in dominant molecular species of triacylglycerols (TAGs) and their spatial distributions within embryo tissues. A combination of mass spectrometry (MS)-based lipidomics approaches, including MS imaging of seed cryo-sections, revealed that cotton embryos expressing a non-functional allele of a Brassica napus delta-12 desaturase showed altered accumulation of TAG species, especially within cotyledonary tissues. While lipid analysis of seed extracts could demonstrate detailed quantitative changes in TAG species in transgenics, the spatial contribution of metabolite compartmentation could only be visualized by MS imaging. Our results suggest tissue-specific differences in TAG biosynthetic pathways within cotton embryos, and indicate the importance of considering the location of metabolites in tissues in addition to their identification and quantification when developing a detailed view of cellular metabolism.

Keywords: Cotton; Dsc; ESI; FA; Gossypium; L; Lipids; MALDI; MS; MSI; Mass spectrometry imaging; O; P; PC; Phospholipids; Sc; TAG; Triacylglycerols; dihydrosterculic (19:0), numerical designation of lipids indicates number of carbons in acyl chains:number of double bonds; electrospray ionization; fatty acids; linoleic (18:2); mass spectrometry; mass spectrometry imaging; matrix-assisted laser desorption/ionization; oleic (18:1); palmitic (16:0); phosphatidylcholine; sterculic (19:1); triacylglycerol.