Identifying new genetic resources to optimize the canola oil profile
Term: 3 years, beginning 2024
Status: Ongoing
Researcher(s): Mark Smith, AAFC
SaskCanola Investment: $127,600
Total Project Cost: $127,600
Funding Partners: N/A
Objective
1. Validate a new reduced saturated fatty acid trait in canola, generate pre-breeding lines and molecular markers.
2. Screen a B. napus mutagenesis population for oil profile traits.
3. Determine why canola quality B. napus does not produce a true zero VLCFA oil.
4. Identify mutant alleles of BnSDP1 to enhance seed oil content.
Project Description
Conventional canola oil and the high oleic (HO) specialty oils are high quality vegetable oils very well suited for human consumption, food preparation and biofuel production. They offer the lowest saturated fatty acid content of any commodity oil with total saturate levels ranging from 7% to as low as 4.5% in some “Low Sat HO” varieties. The very-long-chain fatty acid (VLCFA) erucic acid has been reduce to essentially zero, and HO varieties with 80% oleic acid exist. With these attractive characteristics it is tempting to think that there is nothing more to be done to improve this oil. A close look at seed oil fatty acid composition, and consideration of the limited genetic diversity behind the oil improvement traits suggests that there is opportunity for some additional improvement.
Considering saturated fatty acid content, although levels of saturated fatty acids as low as 4.5% have been achieved, the trait is proprietary and conventional canola is still contains around 7% saturated fatty acid. A review of the patent literature reveals that the basis of the low sat trait in Low Sat HO canola varieties is the presence of mutagenesis derived divergent alleles of genes encoding acyl-acyl carrier protein thioesterase enzymes (orthologues of Arabidopsis FatA2 and FatB). In developing oilseeds, these enzymes control the exit of newly formed fatty acids from their site of synthesis (the plastid) and their channeling towards oil assembly. Studies in the model oilseed Arabidopsis have shown that reducing the activity of these enzymes can alter seed fatty acid profiles, but also negatively impacts oil content. Identifying alternative pathways for saturated fatty acid reduction, for example by increasing their rate of conversion to unsaturated fatty acids would clearly be of interest, and has been successfully demonstrated using transgenic approaches. Maintaining the position of canola oil as the commodity oil with the lowest saturated fatty acid content is very important, particularly as major progress has been made in reducing the saturated fatty acid content of soybean oil. Although commodity soybean oil has a saturated fatty acid content of around 16%, high oleic low sat soybean oils such as Plenish® (12% total sat) are already on the market and Vistive Gold ® (6% total sat) will soon be released by Bayer. The low saturated fatty acid content of the latter variety is clearly a threat to canola oil.
It is well known that canola oil does not contain significant amounts of the very-long chain fatty acid (VLCFA) erucic acid (22:1), but conventional and HO canola oils still contain 1.5% to 2% VLCFAs, primarily the omega-9, 20-Carbon (C20) fatty acid gondoic acid (20:1). Although there have been no reported detrimental effects associated with C20 VLCFAs, and gondoic acid even accounts for 13% of the fatty acids in camelina oil, complete removal of VLCFAs from the seed triacylglycerol of canola would generate an oil more homogeneous for industrial use, improve cloud point and increase oleic acid content. The source of these low level VLCFAs in canola oil is still uncertain. The zero erucic trait in canola is a result of mutations in the two FAE1 genes, located on chromosomes A08 and C03, that encode the enzyme responsible for elongation of oleic acid to erucic acid, with gondoic acid being an intermediate in this elongation process. The mutations are a single base change that alters an amino acid essential for enzyme activity, and a small deletion that may cause a miss-translation of a FAE1 protein. Although it is unlikely that the mutant alleles encode proteins with residual low level activity, this has not been investigated in detail and there is no clear answer as to why VLCFAs have not been completely eliminated from the oil. A fresh investigation of fatty acid elongation in developing seeds of canola and identification of new mutant FAE1 alleles may clarify this uncertainty and enable the complete removal of VLCFAs.
An additional target that still deserves attention is seed oil content. In canola, this has been an objective of extensive research and breeding for many years as a stable increase of even a small percentage would have considerable economic impact. Recent developments in other species have demonstrated that there are promising traits that have not yet been commercially developed in canola, but which deserve investigation. A good example would be the suppression during seed development of the SUCROSE DEPENDANT 1 lipase (SDP1). Activity of this enzyme during seed maturation is known to cause a decrease in the final oil content of the seed as the enzyme breaks down some of the stored oil. Suppression in multiple species has been shown to boost oil content and a very recent study in soybean also reported a reduction in undigestible seed oligosaccharides. There is already proof of concept for the benefit of SDP1 suppression in B. napus from a study using a transgenic approach but suppression could also be achieved through a non transgenic means such as the identification of mutations in SDP1 genes. Interestingly, the previous work suggested that SDP1 downregulation reduced seed longevity with a decline in germination rate after 3 to 4 years for storage. One benefit of this could be to reduce volunteer canola persistence in the soil seed bank.
Although modern genome editing technologies have great potential for targeted crop improvement, natural diversity, or diversity induced through mutagenesis techniques remain as powerful tools for discovery of novel traits and new alleles of known genes. Techniques for the rapid introgression of beneficial alleles are well established and the resulting material is non-transgenic and un-encumbered by technology related IP. New high throughput tools for phenotype screening and genetic characterization are available to uncover diversity and can be applied to uncover new genetic resources that could be used to further optimize the profile of canola oil.
The proposed project is designed to utilize a unique Canadian B. napus genetic diversity resource for targeted canola oil profile optimization. The resource is a chemical mutagenesis (Ethymethanesulfonate, EMS) population of canola type Brassica napus originally developed by Dr George Haughn. The population is currently being maintained Dr Raju Datla at GIFS at the U of S. Although the primary interest of GIFS is phenotyping and genotyping the population with a focus on climate resilience traits, this resource has previously shown promise as a source of diversity for seed related traits. Work in this area is no longer funded. To maintain a reasonable scope and project budget the proposed work will validate a reduced saturated fatty acid trait already identified from the population, screen for additional diversity and use the population to identify and better understand factors controlling seed oil composition and content. The goal is to deliver new variant alleles of genes involved in seed oil synthesis that would have potential for use in improving oil composition and content to maintain the market advantages of canola oil in a highly competitive environment.