Metabolic switching of astringent and beneficial triterpenoid saponins in soybean is achieved by a loss-of-function mutation in cytochrome P450 72A69
Metabolic switching of astringent and beneficial triterpenoid saponins in soybean is achieved by a loss-of-function mutation in cytochrome P450 72A69
复制标题
DOI：
10.1111/tpj.13403
复制
发表时间：
2017-02-01
期刊：
影响因子：
7.2
通讯作者：
Ishimoto, Masao
中科院分区：
文献类型：
--
作者：
Yano, Ryoichi;Takagi, Kyoko;Ishimoto, Masao
三萜皂苷是大豆种子次生代谢产物的主要成分，分为两类：A组皂苷和2，3-二氢-2，5-二羟基-6-甲基-4H-吡喃-4-酮（DSPs）皂苷。A组皂苷的糖苷配基部分由大豆皂精醇A（SA）组成，其是氧化的-香树脂醇产物，并且Doppler皂苷的糖苷配基部分由大豆皂精醇B（SB）组成。A组皂苷在豆制品中产生苦味和涩味，而大豆皂苷对人类具有已知的健康益处。我们完成了基因Sg-5，这是负责SA生物合成的图位克隆和表征。天然存在的sg-5突变体缺乏A组皂苷，并在Glyma 15 g39090中具有功能丧失突变（L164*），Glyma 15 g39090编码细胞色素P450酶CYP 72 A69。酶活性测定表明重组CYP 72 A69对SB具有羟化酶活性，这也表明SA的产生。此外，诱导的Glyma 15 g39090突变体（R44* 或S348 P）缺乏与sg-5突变体类似的A组皂苷，表明Glyma 15 g39090对应于Sg-5。内源性的人参皂苷的水平较高的sg-5突变体比野生型线由于酶的活性，转换SB SA的损失。有趣的是，古多倍体大豆和密切相关的菜豆的基因组在与大豆Sg-5区域同线的基因组区域中携带多个Sg-5旁系同源物。然而，SA在普通菜豆样品中没有积累，表明Sg-5活性在基因复制事件后进化。我们的研究结果表明，在大豆中，通过使Sg-5失活，可以实现不需要的皂苷与有益皂苷的代谢转换。
Triterpenoid saponins are major components of secondary metabolites in soybean seeds and are divided into two groups: group A saponins, and 2,3-dihydro-2,5-dihydroxy-6-methyl-4H-pyran-4-one (DDMP) saponins. The aglycone moiety of group A saponins consists of soyasapogenol A (SA), which is an oxidized -amyrin product, and the aglycone moiety of the DDMP saponins consists of soyasapogenol B (SB). Group A saponins produce a bitter and astringent aftertaste in soy products, whereas DDMP saponins have known health benefits for humans. We completed map-based cloning and characterization of the gene Sg-5, which is responsible for SA biosynthesis. The naturally occurring sg-5 mutant lacks group A saponins and has a loss-of-function mutation (L164*) in Glyma15g39090, which encodes the cytochrome P450 enzyme, CYP72A69. An enzyme assay indicated the hydroxylase activity of recombinant CYP72A69 against SB, which also suggested the production of SA. Additionally, induced Glyma15g39090 mutants (R44* or S348P) lacked group A saponins similar to the sg-5 mutant, indicating that Glyma15g39090 corresponds to Sg-5. Endogenous levels of DDMP saponins were higher in the sg-5 mutant than in the wild-type lines due to the loss of the enzyme activity that converts SB to SA. Interestingly, the genomes of palaeopolyploid soybean and the closely related common bean carry multiple Sg-5 paralogs in a genomic region syntenic to the soybean Sg-5 region. However, SA did not accumulate in common bean samples, suggesting that Sg-5 activity evolved after gene duplication event(s). Our results demonstrate that metabolic switching of undesirable saponins with beneficial saponins can be achieved in soybean by disabling Sg-5.