Heterogeneous Distribution of Erucic Acid in Brassica napus Seeds

Abstract

Brassica napus (B. napus) is the world's most widely grown temperate oilseed crop. Although breeding for human consumption has led to removal of erucic acid from refined canola oils, there is renewed interest in the industrial uses of erucic acid derived from B. napus, and there is a rich germplasm available for use. Here, low-and high-erucic acid accessions of B. napus seeds were examined for the distribution of erucic acid-containing lipids and the gene transcripts encoding the enzymes involved in pathways for its incorporation into triacylglycerols (TAGs) across the major tissues of the seeds. In general, the results indicate that a heterogeneous distribution of erucic acid across B. napus seed tissues was contributed by two isoforms (out of six) of FATTY ACYL COA ELONGASE (FAE1) and a combination of phospholipid:diacylglycerol acyltransferase (PDAT)-and diacylglycerol acyltransferase (DGAT)-mediated incorporation of erucic acid into TAGs in cotyledonary tissues. An absence of the expression of these two FAE1 isoforms accounted for the absence of erucic acid in the TAGs of the lowerucic accession.

Analyzing Mass Spectrometry Imaging Data of 13C-Labeled Phospholipids in Camelina sativa and Thlaspi arvense (Pennycress) Embryos

“…In this study, we imaged labeled molecular species of PC because it is an intermediate for TG synthesis within embryonic development, as well as an important membrane lipid, and it is well suited for MS imaging. Additionally, many other MS imaging studies have found different PC molecular species, varying in their fatty acid composition, are heterogeneously distributed among seed tissues, suggesting a difference in metabolism that may be revealed through isotopic labeling imaging [ 23 , 24 , 25 , 26 , 27 , 28 ]. Hence, imaging the molecular species of PC demonstrates the potential value of 13 C-MSI for lipid metabolism studies.…”

“…While such conclusions require further evidence, including analysis of mutants in PC and TAG biosynthesis, HPLC-MS/MS of extracts from dissected embryonic tissues and MS/MS analysis of labeled metabolites to determine what parts of PC have been labeled, here we demonstrate that combining isotopic labeling of lipids and MSI is able to provide new information about tissue-specific differences in metabolism that would otherwise remain hidden in typical extraction-based methods. Such examination of these metabolic differences will help to provide explanations for the heterogeneity of metabolites observed within different tissues, and will continue to uncover the complex spatial dimension to metabolism [ 22 , 23 , 24 , 25 , 26 , 27 , 28 ].…”

“…Lipid metabolites are particularly well suited to ionization and analysis by MALDI-MS. The imaging of distinct tissue types in seeds (e.g., cotyledons and embryonic axis) has revealed unexpected heterogeneous lipid distributions [ 22 , 23 , 24 , 25 , 26 , 27 , 28 ]. Developing embryos of oilseeds typically accumulate storage lipids during development, up to 30% or more, and are particularly suited to this spatial analysis.…”

CRISPR/Cas9-Induced fad2 and rod1 Mutations Stacked With fae1 Confer High Oleic Acid Seed Oil in Pennycress (Thlaspi arvense L.)

“…PC is an important structural membrane lipid in seeds and is also an intermediate in the biosynthesis of TAG. Given that different molecular species of PC and TAG have been found to be distributed in an unequal manner in seed tissues of many plant species (Marmon et al, 2017;Woodfield et al, 2017;Lu et al, 2018Lu et al, , 2020Sturtevant et al, 2019), it was not clear how the mutant genotypes generated here would influence those normal distributions. MALDI-MS imaging allows for a comprehensive view of the lipid metabolites distributed in seed sections.…”

“…Like PC, different TAG molecular species of oilseeds have previously been observed to localize preferentially to different seed tissues (Marmon et al, 2017;Woodfield et al, 2017;Lu et al, 2018Lu et al, , 2020Sturtevant et al, 2019). In wild-type seeds, the most abundant TAG molecular species were the erucic acid-containing TAG-62:4, 62:5 (Figure 6) and TAG-60:4, 60:5 (Supplementary Figure 8), preferentially localized to the cotyledons, while the embryonic axis showed a relative enrichment in 52 and 54 carbon TAG species (Supplementary Figure 8 and Figure 6).…”