Two independent variant raffinose synthase 3 (RS3) alleles produced an equivalent phenotype and implicated the gene as a key contributor to soybean seed carbohydrate phenotype. Soybean is an important crop because the processed seed is utilized as a vegetable oil and a high protein meal typically used in livestock feeds. Raffinose and stachyose, the raffinose family of oligosaccharides (RFO) carbohydrate components of the seed, are synthesized in developing soybean seeds from sucrose and galactinol. Sucrose is considered positive for metabolizable energy, while RFO are anti-nutritional factors in diets of monogastric animals such as humans, poultry, and swine. To increase metabolizable energy available in soybean seed meal, prior research has been successful in deploying variant alleles of key soybean raffinose synthase (RS) genes leading to reductions or near elimination of seed RFO, with significant increases in seed sucrose. The objective of this research was to investigate the specific role of variants of the RS3 gene in a genomic context and improve molecular marker-assisted selection for the ultra-low (UL) RFO phenotype in soybean seeds. The results revealed a new variant of the RS3 allele (rs3 snp5, rs3 snp6) contributed to the UL RFO phenotype when mutant alleles of RS2 were present. The variant RS3 allele identified was present in about 15% of a small set of soybean cultivars released in North America. A missense allele of the RS3 gene (rs3 G75E) also produced the UL RFO phenotype when combined with mutant alleles of RS2. The discoveries reported here enable direct marker-assisted selection for an improved soybean meal trait that has the potential to add value to soybean by improving the metabolizable energy of the meal.

中文翻译：

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分子辅助育种以改善大豆种子的碳水化合物特征。


两个独立的棉子糖合酶 3 (RS3) 等位基因变体产生了相同的表型，并表明该基因是大豆种子碳水化合物表型的关键贡献者。大豆是一种重要的作物，因为加工后的种子可用作植物油和通常用于牲畜饲料的高蛋白粉。棉子糖和水苏糖是种子低聚糖 (RFO) 碳水化合物成分的棉子糖家族，是在大豆种子发育过程中由蔗糖和半乳糖醇合成的。蔗糖被认为对代谢能有积极作用，而 RFO 是单胃动物（如人类、家禽和猪）饮食中的抗营养因子。为了增加大豆籽粕中可用的代谢能，先前的研究已成功地利用关键大豆棉子糖合酶 (RS) 基因的变体等位基因，从而减少或接近消除种子 RFO，同时显着增加种子蔗糖。本研究的目的是调查 RS3 基因变体在基因组背景中的具体作用，并改进大豆种子中超低 (UL) RFO 表型的分子标记辅助选择。结果表明，当 RS2 的突变等位基因存在时，RS3 等位基因的新变体（rs3 snp5、rs3 snp6）会导致 UL RFO 表型。在北美发布的一小部分大豆品种中，约有 15% 存在这种变异的 RS3 等位基因。当与 RS2 的突变等位基因结合时，RS3 基因的错义等位基因 (rs3 G75E) 也产生 UL RFO 表型。这里报道的发现使得能够直接标记辅助选择改良的豆粕性状，该性状有可能通过提高豆粕的代谢能来增加大豆的价值。