Genetic analysis of variation in sugar chain composition at the C-22 position of group A saponins in soybean, Glycine max (L.) Merrill

Abstract

Saponins are a diverse group of secondary metabolites widely distributed in plants. Some saponins in soybean seeds have medicinal properties, but the terminal acetylated sugar at the C-22 position of group A saponins in seed hypocotyls causes a bitter and astringent taste. We used cultivated and wild soybean accessions classified into four different group A saponin phenotypes, including non-acetylated A0-αg and deacetyl-Af, as parents to obtain four F 2 populations and a population of recombinant inbred lines to test their genetic relationship. The gene controlling the phenotype of the group A saponins in each line was mapped near the simple sequence repeat marker Satt336 on soybean chromosome 7 (linkage group M). An allelism test of the A0-αg and deacetyl-Af variants revealed no segregation of Aa and Ab phenotypes in the progeny, although the genes controlling the two phenotypes have been assigned to two different loci, Sg-1 and Sg-2. These results suggest that the four group A saponin phenotypes are controlled by multiple alleles at the single locus Sg-1.

Achievements and Challenges in Improving the Nutritional Quality of Food Legumes

“…Inter-conversions among saponins and the complexity of their modifications seem to involve a number of glycosyltransferases and acetylases, and are implicated in the generation of bitterness and astringeny. Mutants, identified in soybean and wild soybean (Glycine soja), have defined two genetic loci, Sg-1 and Sg-2, that control these phenotypes (Takada et al, 2010). In pea, the modified saponin named DDMP (2,3-dihydro-2,5-dihydroxy-6-methyl-4H-pyran-4-one)-saponin, has been implicated in bitterness and it has been suggested that this and related compounds could interact negatively or positively with seed protein components (Heng et al, 2004).…”

The Sg-1 Glycosyltransferase Locus Regulates Structural Diversity of Triterpenoid Saponins of Soybean

“…The biosynthesis of saponin A0-ag results from a recessive allele, sg-1 0 , at the same locus (Kikuchi et al, 1999;Takada et al, 2010). Here, we describe the identification of multiple alleles of the Sg-1 locus that are responsible for the structural diversity of the terminal sugar at the C-22 position of group A saponins.…”

“…Both have an acetylated sugar at the terminal position ( Figure 1A) that causes the undesirable aftertaste (Kitagawa et al, 1988;Taniyama et al, 1988b;Okubo et al, 1992). By screening more than 1000 germplasm stocks, a soybean cultivar and a wild accession were found to accumulate saponin A0-ag, which lacks the acetylated terminal sugar at the C-22 position ( Figure 1A) (Kikuchi et al, 1999;Takada et al, 2010). These findings led to breeding of cultivars useful for human food, such as Kinusayaka, which reduces the bitter taste and astringent effects (Kato et al, 2007).…”

Metabolic switching of astringent and beneficial triterpenoid saponins in soybean is achieved by a loss‐of‐function mutation in cytochrome P450 72A69

“…Soybean ( Glycine max (L.) Merr.) is one of the most economically important crop plants worldwide and triterpenoid saponins are major components of secondary metabolites in its mature seeds (Tsukamoto et al ., ; Takada et al ., , ). Saponins comprise more than 2% of the dry weight of the hypocotyl in developed mature seeds (Fenwick et al ., ), and are characterized as group A saponins or 2,3‐dihydro‐2,5‐dihydroxy‐6‐methyl‐4 H ‐pyran‐4‐one (DDMP) saponins based on their chemical structures.…”

“…The diversity of sugar moieties in soybean saponins is influenced by seven alleles at three different loci: Sg‐1 , Sg‐3 , and Sg‐4 (Shiraiwa et al ., ; Tsukamoto et al ., ; Kikuchi et al ., ; Takada et al ., , ). Sg‐1 ( Glyma07g38460 ) was recently cloned and encodes a uridine diphosphate (UDP)‐sugar‐dependent glycosyltransferase (Sayama et al ., ).…”