Triterpene saponins are a diverse group of biologically functional products in plants. Saponins usually are glycosylated, which gives rise to a wide diversity of structures and functions. In the group A saponins of soybean (Glycine max), differences in the terminal sugar species located on the C-22 sugar chain of an aglycone core, soyasapogenol A, were observed to be under genetic control. Further genetic analyses and mapping revealed that the structural diversity of glycosylation was determined by multiple alleles of a single locus, Sg-1, and led to identification of a UDP-sugar-dependent glycosyltransferase gene (Glyma07g38460). Although their sequences are highly similar and both glycosylate the nonacetylated saponin A0-ag, the Sg-1 a allele encodes the xylosyltransferase UGT73F4, whereas Sg-1 b encodes the glucosyltransferase UGT73F2. Homology models and site-directed mutagenesis analyses showed that Ser-138 in Sg-1 a and Gly-138 in Sg-1 b proteins are crucial residues for their respective sugar donor specificities. Transgenic complementation tests followed by recombinant enzyme assays in vitro demonstrated that sg-1 0 is a loss-of-function allele of Sg-1. Considering that the terminal sugar species in the group A saponins are responsible for the strong bitterness and astringent aftertastes of soybean seeds, our findings herein provide useful tools to improve commercial properties of soybean products.

Although certain saponins in soybean seeds have been reported to have health benefits, group A acetyl saponins cause undesirable bitter and astringent tastes in soy products. Therefore, reduction or elimination of group A saponins is an important target for soybean breeders. A wide survey of cultivated and wild soybean germplasm identified a mutant line that lacked group A saponins. The absence of soyasapogenol A, a group A saponin aglycone, is controlled by a single recessive allele, sg-5 that mapped genetically near the SSR marker, Satt117, on soybean chromosome 15 (linkage group E). The locus is epistatic to Sg-1, which controls the terminal sugar variation on the C-22 sugar chain of soyasapogenol A, and allelic differences at this locus lead to changes in the amount of DDMP saponins and their derivatives group B and E products. These findings provide a new insight into the biosynthetic pathway of soybean saponins, and identify a genetic approach that can be applied to improve the quality of foods produced from soybean.

Among commonly applied molecular markers, simple sequence repeats (SSRs, or microsatellites) possess advantages such as a high level of polymorphism and codominant pattern of inheritance at individual loci. To facilitate systematic and rapid genetic mapping in soybean, we designed a genotyping panel comprised 304 SSR markers selected for allelic diversity and chromosomal location so as to provide wide coverage. Most primer pairs for the markers in the panel were redesigned to yield amplicons of 80–600 bp in multiplex polymerase chain reaction (PCR) and fluorescence-based sequencer analysis, and they were labelled with one of four different fluorescent dyes. Multiplex PCR with sets of six to eight primer pairs per reaction generated allelic data for 283 of the 304 SSR loci in three different mapping populations, with the loci mapping to the same positions as previously determined. Four SSRs on each chromosome were analysed for allelic diversity in 87 diverse soybean germplasms with four-plex PCR. These 80 loci showed an average allele number and polymorphic information content value of 14.8 and 0.78, respectively. The high level of polymorphism, ease of analysis, and high accuracy of the SSR genotyping panel should render it widely applicable to soybean genetics and breeding.

Saponins are sterols or triterpene glycosides that are widely distributed in plants. The biosynthesis of soybean saponins is thought to involve many kinds of glycosyltransferases, which is reflected in their structural diversity. Here, we performed linkage analyses of the Sg-3 and Sg-4 loci, which may control the sugar chain composition at the C-3 sugar moieties of the soybean saponin aglycones soyasapogenols A and B. The Sg-3 locus, which controls the production of group A saponin Af, was mapped to chromosome (Chr-) 10. The Sg-4 locus, which controls the production of DDMP saponin βa, was mapped to Chr-1. To elucidate the preference of sugar chain formation at the C-3 and C-22 positions, we analyzed the F2 population derived from a cross between a mutant variety, Kinusayaka (sg-10), for the sugar chain structure at C-22 position, and Mikuriya-ao (sg-3), with respect to the segregation of the composition of the group A saponins, and found that the formation of these sugar chains was independently regulated. Furthermore, a novel saponin, predicted to be A0-γg, 3-O-[β-d-galactopyranosyl (1→2)-β-d-glucuronopyranosyl]-22-O-α-l-arabinopyranosyl-soyasapogenol A, appeared in the hypocotyl of F2 individuals with genotype sg-10/sg-10 sg-3/sg-3.

2461ReseaRch S oybean develops inflorescence meristems on each node, including the shoot apex. The flower clusters of the soybean raceme have a highly branched inflorescence structure, and their racemes are classified as terminal, primary, secondary, tertiary, and so on (Torigoe et al., 1982). Previous studies have reported a relationship between pod setting and raceme order. The increased yield of soybean at higher densities is associated with an increased share of pods of lower-order racemes (Kuroda et al., 1992). Pod setting and seed growth of the lower-order racemes is more important than higher-order racemes in determining soybean yield because seeds derived from lower-order racemes account for the majority of the yield (Isobe et al., 1995).Some studies have focused on the terminal raceme, the lowestorder raceme, or its length. It was found that TRL measurements could possibly be used to predict yield in the semideterminate aBSTRaCT Soybean [Glycine max (L.) Merr.] develops inflorescence meristems on each node, including the shoot apex. The flower clusters of the soybean raceme have a highly branched inflorescence structure, and their racemes are classified as terminal, primary, secondary, and so on. raceme phenotype is an important trait associated with the number of floral buds and pods, and is dependent on the genotype. The breeding line 1532-1 was characterized by remarkably long racemes at the shoot apex of the main stem. To identify quantitative trait loci (QTLs) conditioning the terminal raceme length (TrL), a recombinant inbred line (rIL) population was developed from a cross between 1532-1 and an ordinary cultivar, Toyoharuka. The rILs were divided into two groups according to their alleles for a maturity locus, E1. The early-maturing rIL group with the e1 genotype was used for QTL analysis of TrL, while the late-maturing rIL group with the E1 genotype could not mature normally and lodged severely. Analysis of the early-maturing group resulted in the identification of a stable QTL, qTRL18-1, where the 1532-1 allele had a positive effect on TrL. Another QTL, qTRL11-1, was detected only in the rILs with the 1532-1 alleles at the qTRL18-1 locus, indicating an interaction between qTRL18-1 and qTRL11-1. The qTRL18-1 locus was located in the proximal region of the Dt2 locus. No stable QTLs for flowering time or maturing time were detected in the proximal region of qTRL18-1 or qTRL11-1. our results provide a new strategy to increase pod number on the main stem by marker-assisted selection (MAS) for qTRL18-1 and qTRL11-1.

Black soybean landraces that had been cultivated in Tanba region and the neighboring regions and conserved black soybean landraces, including those from other regions in Japan, were used in this study. The polymorphisms of 78 SSR markers in nuclear DNA and 6 SSRs in chloroplast DNA were analyzed in the black soybean landrace populations. The result of phylogenic analysis revealed that the black soybeans can be classified into six clades. The landraces originating from Tanba region were classed into first and second clades, and two chloroplast genotypes were found in the population of black soybeans from the Tanba region. Genotype A chloroplast was predominantly identified in major populations of the Tanba, while genotype B was widely distributed in the black soybean population. Population structure analysis in the Japanese black soybean accessions inferred there are six groups. The black soybean landrace from the Tanba region was classified into three groups, mainly corresponding to the distance-based phylogenic results. The two groups were probably derived from different ancestors with Type A and B chloroplast genomes, respectively, whereas the other group showed both types of chloroplast genome. The admixture situations suggested that the landraces in the main group have been widely cultivated in Tanba region, while the landraces that belong to other groups were cultivated in localized area. Several phenotypes were compared among genotype groups, dividing into two sub-groups: founder sub-group and admixed sub-group. Phenotypic differences were observed between founder landraces in group 1 and group 3. On the other hand, landraces in admixture landraces in group 1 and group 2 segregated for several traits, while founder landraces in group 1 were stabled for each trait. These observations suggest that gene flow events have occurred between different founder landraces.

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