State Key Laboratory of Plant Genomics, Institute of Genetics and Developmental Biology, The Innovative Academy of Seed Design, the Chinese Academy of Sciences, Beijing, 100101, China.
College of Advanced Agricultural Sciences, University of Chinese Academy of Sciences, Beijing, 100039, China.
J Integr Plant Biol. 2023 Nov;65(11):2490-2504. doi: 10.1111/jipb.13553. Epub 2023 Sep 13.
Soyasaponins are major small molecules that accumulate in soybean (Glycine max) seeds. Among them, type-A soyasaponins, fully acetylated at the terminal sugar of their C22 sugar chain, are responsible for the bitter taste of soybean-derived foods. However, the molecular basis for the acetylation of type-A soyasaponins remains unclear. Here, we identify and characterize GmSSAcT1, encoding a BADH-type soyasaponin acetyltransferase that catalyzes three or four consecutive acetylations on type-A soyasaponins in vitro and in planta. Phylogenetic analysis and biochemical assays suggest that GmSSAcT1 likely evolved from acyltransferases present in leguminous plants involved in isoflavonoid acylation. Loss-of-function mutants of GmSSAcT1 exhibited impaired seed germination, which attribute to the excessive accumulation of null-acetylated type-A soyasaponins. We conclude that GmSSAcT1 not only functions as a detoxification gene for high accumulation of type-A soyasaponins in soybean seeds but is also a promising target for breeding new soybean varieties with lower bitter soyasaponin content.
大豆皂甙是大豆（Glycine max）种子中积累的主要小分子物质。其中，完全乙酰化 C22 糖链末端糖的 A 型大豆皂甙是导致大豆衍生食品苦味的原因。然而，A 型大豆皂甙的乙酰化分子基础仍不清楚。本研究鉴定并表征了 GmSSAcT1，它编码 BADH 型大豆皂甙乙酰转移酶，能够在体外和体内催化 A 型大豆皂甙的三个或四个连续乙酰化反应。系统发育分析和生化分析表明，GmSSAcT1 可能是从参与异黄酮酰化的豆科植物中的酰基转移酶进化而来的。GmSSAcT1 的功能丧失突变体表现出种子发芽受损，这归因于无乙酰化 A 型大豆皂甙的过度积累。我们的结论是，GmSSAcT1 不仅是大豆种子中 A 型大豆皂甙高积累的解毒基因，也是培育苦味低大豆皂甙含量新大豆品种的有前途的目标。
