Abstract
Seeds of soybean (Glycine max L.) are a major source of plant-derived oils. In the past, improvements have been made in the quantity and quality of seed oil. Triacylglycerols (TAGs) are the principal components of soybean seed oil, and understanding the metabolic regulation of TAGs in soybean seeds is essential. Here, we identified four soybean genes encoding TAG lipases, designated as SUGAR DEPENDENT1-1 (GmSDP1-1), GmSDP1-2, GmSDP1-3 and GmSDP1-4; these are homologous to Arabidopsis thaliana SDP1 (AtSDP1). To characterize the function of these genes during grain filling, transgenic lines of soybean were generated via RNA interference to knockdown the expression of all four GmSDP1 genes. The seed oil content of the transgenic soybean lines was significantly increased compared with the wild type (WT). Additionally, fatty acid profiles of the WT and transgenic soybean lines were altered; the content of linoleic acid, a major fatty acid in soybean seeds, was significantly reduced, whereas that of oleic acid was increased in transgenic soybean seeds compared with the WT. Substrate specificity experiments showed that TAG lipase preferentially cleaved oleic acid than linoleic acid in the oil body membrane in WT soybean. This study demonstrates that the GmSDP1 proteins regulate both the TAG content and fatty acid composition of soybean seeds during grain filling. These results provide a novel strategy for improving both the quantity and quality of soybean seed oil.
Highlights
Plant oils have diverse uses; they have been utilised as dietary oils, soaps, and industrial materials
To identify soybean genes orthologous to Arabidopsis SUGAR DEPENDENT1 (SDP1) (AtSDP1) gene, amino acid sequences containing patatin-like phospholipase domain (PF01734), were acquired from the soybean genome using Phytozome v12.1.629
Phylogenetic analysis of 29 sequences containing the domain of PF01734 from soybean genome was performed, which revealed that four lipase sequences (Glyma.02g190000.1, Glyma10g105200.1, Glyma19g132900.1 and Glyma03g130900.1) belonged to the same clade as Arabidopsis thaliana SDP1 (AtSDP1) (Fig. 1); we designated these four sequences as GmSDP1-1, GmSDP1-2, GmSDP1-3 and GmSDP1-4, respectively
Summary
Plant oils have diverse uses; they have been utilised as dietary oils, soaps, and industrial materials. TAG degradation is essential for the post-germinative growth of oilseed crop plants[14,15,16]. Defective SDP1 has been shown to enhance the seed oil content in Arabidopsis (Arabidopsis thaliana)[24], rapeseed[25], and Jatropha (Jatropha curcas)[26]. These reports suggest that TAG turnover is highly active in developing seeds, and the suppression of TAG degradation enhances the oil content of seeds. Several crops with altered fatty acid composition such as canola, a rapeseed variant with low erucic acid (22:1) content, are wildly cultivated. Further investigation of the TAG metabolic pathway is needed to develop soybean cultivars with high oil and low PUFA content
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