Abstract
Rapeseed (Brassica napus L.) is a vital oil crop worldwide. High oleic acid content is a desirable quality trait for rapeseed oil, which makes it more beneficial to human health. However, many germplasm resources with high oleic acid content in rapeseed have not been evaluated with regard to their genotypes, making it difficult to select the best strains with this trait for the breeding of high oleic acid rapeseed variety. This work was to explore the gene-regulation mechanism of this trait using a new super-high oleic acid content (∼85%) line N1379T as genetic material. In this study, the sequences of four homologous fatty acid desaturase (BnFAD2) genes were compared between super-high (∼85%, N1379T) and normal (∼63%) oleic acid content lines. Results showed that there were two single-nucleotide polymorphisms (SNPs) in BnFAD2-1 and BnFAD2-2, respectively, which led to the amino acid changes (E106K and G303E) in the corresponding proteins. Functional analysis of both genes in yeast confirmed that these SNPs were loss-of-function mutations, thus limiting the conversion of oleic acid to linoleic acid and resulting in the considerable accumulation of oleic acid. Moreover, two specific cleaved amplified polymorphic sequences (CAPS) markers for the two SNPs were developed to identify genotypes of each line in the F2 and BC1 populations. Furthermore, these two mutant loci of BnFAD2-1 and BnFAD2-2 genes were positively associated with elevated oleic acid levels and had a similar effect with regard to the increase of oleic acid content. Taken together, these two novel SNPs in two different BnFAD2 genes jointly regulated the high oleic acid trait in this special germplasm. The study provided insight into the genetic regulation involved in oleic acid accumulation and highlighted the use of new alleles of BnFAD2-1 and BnFAD2-2 in breeding high oleic acid rapeseed varieties.
Highlights
Rapeseed (Brassica napus L.) is one of the most important oil crops across the world
Results showed that the cloned sequences and those from GenBank and reference genome were highly similar and all four BnFAD2 genes shared identical start and termination coding fragments, which allowed us to design the P1-P2 primer pair to clone all of the homologous BnFAD2 genes (Figure 1A; Supplementary Table S2)
The BnFAD2 gene sequences of the lines (N1379T/16wh53) were divided into the four groups corresponding to BnFAD2-1 (48/55 sequences), BnFAD22 (45/50 sequences), BnFAD2-3 (40/44 sequences), and BnFAD24 (73/62 sequences)
Summary
Rapeseed (Brassica napus L.) is one of the most important oil crops across the world. Similar to other vegetable oils, the fatty acid composition of rapeseed oil is the key trait involved in its utilization mode and range (Napier et al, 2014). Rapeseed oil with higher oleic acid (>75%) has several advantages compared with non-high oleic acid varieties: (1) its anti-oxidative ability provides a longer shelf life, eliminating the need for a hydrogenation process (Browse et al, 1998; Lauridsen et al, 1999; Przybylski et al, 2013); (2) it can decrease low-density lipoprotein levels in humans and decrease the risk of cardiovascular disease (Chang and Huang, 1998; WHO, 2003); and (3) it is a more cost-effective alternative to olive oil in daily cooking processes, while having a similar function, fatty acid composition, and taste. Increasing oleic acid content in rapeseed oil has been one of the major objectives for researchers focus on improving rapeseed oil quality
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