多花黄精甾体皂苷生物合成途径分析及关键酶基因研究

Identification of key enzyme genes involved in biosynthesis of steroidal saponins and analysis of biosynthesis pathway in Polygonatum cyrtonema

甾体皂苷是黄精属植物的特征性成分及主要活性成分,黄精属甾体皂苷具有调节血糖、防治心脑血管疾病及抗肿瘤等多种药理活性。为解析黄精甾体皂苷生物合成途径,探究其关键酶基因,该研究使用BGISEQ-500平台对多花黄精的花、叶、根和根茎进行转录组测序,获得129989条unigenes,88958条unigenes被七大数据库注释,其中22813条unigenes可归类于53个GO功能分类中,64877条unigenes涉及136条KEGG代谢通路。502条unigenes涉及多花黄精甾体皂苷生物合成途径,其中97条unigenes编码甾体皂苷生物合成途径12个关键酶。对甾醇生物合成过程中的第一个关键酶环阿屯醇合酶进行序列分析和同源建模发现其具有保守的催化结构域和底物结合结构域。将多花黄精根茎与花、叶、根的基因表达水平比较,有2437条unigenes在根茎中特异性高表达且被KEGG注释,其中35条与甾体皂苷生物合成途径相关。该研究极大地丰富了黄精属植物的转录组数据,为植物甾体皂苷生物合成途径的解析提供了线索,为进一步研究甾体皂苷生物合成途径关键酶的功能及调控机制奠定了基础。

Steroidal saponins,which are the characteristic and main active constituents of Polygonatum,exhibit a broad range of pharmacological functions,such as regulating blood sugar,preventing cardiovascular and cerebrovascular diseases and anti-tumor.In this study,we performed RNA sequencing(RNA-Seq)analysis for the flowers,leaves,roots,and rhizomes of Polygonatum cyrtonema using the BGISEQ-500 platform to understand the biosynthesis pathway of steroidal saponins and study their key enzyme genes.The assembly of transcripts for four tissues generated 129989 unigenes,of which 88958 were mapped to several public databases for functional annotation,22813 unigenes were assigned to 53 subcategories and 64877 unigenes were annotated to 136 pathways in KEGG database.Furthermore,502 unigenes involved in the biosynthesis pathway of steroidal saponins were identified,of which 97 unigenes encoding 12 key enzymes.Cycloartenol synthase,the first key enzyme in the pathway of phytosterol biosynthesis,showed conserved catalytic domain and substrate binding domain based on sequence analysis and homology modeling.Differentially expressed genes(DEGs)were identified in rhizomes as compared to other tissues(flowers,leaves or roots).The 2437 unigenes annotated by KEGG showed rhizome-specific expression,of which 35 unigenes involved in the biosynthesis of steroidal saponins.Our results greatly extend the public transcriptome dataset of Polygonatum and provide valuable information for the identification of candidate genes involved in the biosynthesis of steroidal saponins and other important secondary metabolites.