Identification of corresponding genes for three low-α-linolenic acid mutants and elucidation of their contribution to fatty acid biosynthesis in soybean seed

In order to keep the quality of vegetable oil stable, it is important to reduce the α-linolenic acid content. Previously, we developed three low-α-linonenic acid soybean mutants, 'J18', 'M5', and 'M24'. In this study, we obtained and characterized four cDNAs, GmFAD3-1a, GmFAD3-1b, GmFAD3-2a, and GmFAD3-2b, encoding microsomal ω-3 fatty acid desaturase from soybean developing seeds. The GmFAD3-1b transcript does not accumulate in the 'J18' mutant, whereas 'M5' and 'M24' contain a 19-base pair and a single-base pair deletion in the coding region of the GmFAD3-1b and GmFAD3-1a genes, respectively. Furthermore, heterologous expression of these two mutant genes in Saccharomyces cerevisiae revealed that the COOH-terminal region of both mutant gene products is essential for their enzymatic activity. In this report, we also discuss the contribution of each microsomal ω-3 fatty acid desaturase gene for α-linolenic acid biosynthesis in soybean seeds.