Fan Yan

The glycosylation patterns of flavonol glycosides (FGs) in soybean leaves are associated with productivity and insect resistance. The structure of FGs is conditioned by four flavonoid glycoside glycosyltransferase (FGG) genes, Fg1 (6"-glucoside present), Fg2 (6"-rhamnoside present), Fg3 (2"-glucoside present), and Fg4 (2"-rhamnoside present). We previously cloned and characterized the Fg1 to Fg3 genes. This study was conducted to comprehensively identify FGG genes by isolating the Fg4 gene. Leaves of the cultivar, Clark (Fg4 allele), contained FGs with rhamnose at the 4"-position, whereas those of the cultivar A.K. (fg4 allele), were devoid of 4"-rhamnoside. Their F₂ population segregated in three Clark-type: 1 A.K.-type ratios, suggesting that a single gene controlled the existence of 4"-rhamnoside. Based on genetic mapping, we cloned a candidate gene, Glyma.06G235000, with three amino acid substitutions between cultivars. Recombinant protein of Clark acted on kaempferol 3-O-rhamnosyl-(1→6)-galactoside and generated a product with a similar retention time to kaempferol 3-O-rhamnosyl-(1→4)-[rhamnosyl-(1→6)-glalactoside]. Furthermore, it acted on kaempferol 3-O-glucoside/galactoside and generated products with similar retention times to kaempferol 3-O-rhamnosyl-(1→2)-glucoside/galactoside. The A.K. protein did not function presumably due to G293R mutation. The cleaved amplified polymorphic sequence (CAPS) marker to detect the mutation co-segregated with FG composition. These results suggest that Glyma.06G235000 corresponds to the Fg4 gene and that the protein attaches rhamnose to the 2"- or 4"-position, depending on the substrates. Information of all FGG genes may be useful for developing cultivars with the desired FGG composition.

Soybean (Glycine max) is the main oilseed crop that provides vegetable oil for human nutrition. The main objective of its breeding research is to increase the total oil content. In the Kennedy pathway, Diacylglycerol acyltransferase (DGAT) is a rate-limiting enzyme that converts diacylglycerol (DAG) to triacylglycerol (TAG). Here, the AhDGAT3 gene was cloned from peanut and overexpressed in the wild-type (WT) Arabidopsis. The total fatty acid content in T₃AhDGAT3 transgenic Arabidopsis seeds was 1.1 times higher on average than that of the WT. Therefore, AhDGAT3 was transferred into the WT (JACK), and four T₃ transgenic soybean lines were obtained, which proved to be positive using molecular biological detection. Specific T-DNA insertion region location information was also obtained via genome re-sequencing. The results of high-performance gas chromatography showed that the contents of oleic acid (18:1) composition and total fatty acids in transgenic soybean plants were significantly higher than that of the WT. However, linoleic acid (18:2) was much lower compared to the WT. The agronomic trait survey showed that the quantitative and yield traits of AhDGAT3 transgenic soybean were better than those of the WT. These results suggest that fatty acids in transgenic soybeans, especially oleic acid and total fatty acid, are enhanced by the over-expression of AhDGAT3.