Abstract
Fatty acid elongase 1 (FAE1) and delta-12 fatty acid desaturase 2 (FAD2) are two key enzymes in plant fatty acid biosynthesis pathway. Five different types of transgenic lines with identical genetic background were developed by single and double-expression regulation of the genes coding for these two key enzymes in the same Brassica napus variety CY2. Seeds of the five types of transgenic lines and the wild-type control, which were planted under the same environmental conditions, were analyzed and compared for fatty acid composition and oil content in the present study. The results showed that the contents of multiple fatty acids, such as oleic, linoleic, linolenic, eicosenoic and erucic acid, could be significantly altered by single and double regulation of the two genes. Particularly in the seeds in which the two endogenous target genes were simultaneously silenced, the oleic acid content was increased to 82.8% from 20.5% of CY2, and in the seeds with grain-specific expression of Arabidopsis thaliana FAE1 gene, the erucic acid content was raised to 60.2% from 43.9% of CY2. Compared with the wild-type control, the relative ratios of eighteen-carbon unsaturated fatty acids and the oleic desaturation proportion were all markedly changed in the five types of transgenic seeds. In addition, it was found that the seed oil content was improved by enhanced expression of FAE1 and decreased by silencing of FAE1 and FAD2 , suggesting that the synthesis and accumulation of seed oil would be influenced to a certain extent by genetic manipulation of the two key enzyme genes.
Highlights
In the fatty acid biosynthesis pathway, fatty acid elongase 1 (FAE1), as one of the four constituent enzymes of fatty acid elongase complex, is the rate limiting enzyme of carbon chain extension reaction with oleic acid as precursor in seeds and the key enzyme of the biosynthesis of very long chain fatty acids with more than C20, while delta-12 fatty acid desaturase 2 (FAD2) plays a key role in catalyzing the desaturation of oleic acid to produce linoleic acid and linolenic acid (Wang et al, 2020)
1.1 Fatty acid composition of transgenic lines The results of fatty acid composition analysis showed that the silencing of endogenous BnFAE1 gene in RNA interference mediated Brassica napus effectively inhibited the carbon chain extension reaction with oleic acid as the starting substrate, which directly led to a significant reduction in the synthesis of very long chain fatty acids with more than C20, and a large amount of oleic acid accumulated
Previous studies have shown that the BnFAE1 gene from high erucic acid varieties was expressed in the seeds of Brassica napus acceptor varieties with an erucic acid content of less than 1%, and the erucic acid and very long chain fatty acid contents were increased by nearly 30% and 40% respectively (Han et al, 2001)
Summary
In the fatty acid biosynthesis pathway, fatty acid elongase 1 (FAE1), as one of the four constituent enzymes of fatty acid elongase complex, is the rate limiting enzyme of carbon chain extension reaction with oleic acid as precursor in seeds and the key enzyme of the biosynthesis of very long chain fatty acids with more than C20, while delta-12 fatty acid desaturase 2 (FAD2) plays a key role in catalyzing the desaturation of oleic acid to produce linoleic acid and linolenic acid (Wang et al, 2020). In the transgenic improvement of fatty acid composition in Brassica napus, the same high-oil variety was used as the receptor parent to systematically study the genetic regulation of FAE1 and FAD2 genes, and various types of single-gene and double-gene transformants with the same genetic background were obtained (Shi et al, 2015; Lang et al, 2016; Shi et al, 2016; Shi et al, 2017). The quality of the seeds of these transgenic lines and their receptor parents planted under the same environmental conditions was analyzed, which could provide a basis for a more comprehensive understanding of the role of these two target genes in the genetic regulation of fatty acid biosynthesis
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