Comparative transcriptome analysis of different tissues of Rheum tanguticum Maxim. ex Balf. (Polygonaceae) reveals putative genes involved in anthraquinone biosynthesis

Abstract Rheum tanguticum is a perennial herb and an important medicinal plant, with anthraquinones as its main bioactive compounds. However, the specific pathway of anthraquinone biosynthesis in rhubarb is still unclear. The accumulation of anthraquinones in different tissues (root, leaf, stem and seed) of R. tanguticum revealed considerable variation, suggesting possible differences in metabolite biosynthetic pathways and accumulation among various tissues. To better illustrate the biosynthetic pathway of anthraquinones, we assembled transcriptome sequences from the root, leaf, stem and seed tissues yielding 157,564 transcripts and 88,142 unigenes. Putative functions could be assigned to 56,911 unigenes (64.57%) based on BLAST searches against annotation databases, including GO, KEGG, Swiss-Prot, NR, and Pfam. In addition, putative genes involved in the biosynthetic pathway of anthraquinone were identified. The expression profiles of nine unigenes involved in anthraquinone biosynthesis were verified in different tissues of R. tanguticum by qRT-PCR. Various transcription factors, including bHLH, MYB_related, and C2H2, were identified by searching unigenes against plantTFDB. This is the first transcriptome analysis of different tissues of R. tanguticum and can be utilized to describe the genes involved in the biosynthetic pathway of anthraquiones, understanding the molecular mechanism of active compounds in R. tanguticum.

摘要 唐古特大黄（Rheum tanguticum）为多年生草本药用植物，其主要生物活性成分为蒽醌类（anthraquinones）化合物。然而，唐古特大黄中蒽醌类化合物的特异性生物合成途径至今仍未明确。对唐古特大黄不同组织（根、叶、茎与种子）中蒽醌类的积累量检测发现其存在显著差异，提示不同组织的代谢物生物合成通路与积累模式可能存在分化。为进一步阐明蒽醌类的生物合成通路，本研究对其根、叶、茎和种子组织的转录组序列进行组装，共获得157564条转录本（transcript）与88142条单基因簇（unigene）。通过比对GO、KEGG、Swiss-Prot、NR及Pfam等注释数据库，可对56911条单基因簇（占比64.57%）完成功能注释。此外，本研究还鉴定得到参与蒽醌类生物合成的候选基因。通过实时荧光定量聚合酶链反应（qRT-PCR），验证了9个参与蒽醌类生物合成的单基因簇在唐古特大黄不同组织中的表达谱。通过植物转录因子数据库（plantTFDB）检索单基因簇，共鉴定得到包括bHLH、MYB相关及C2H2在内的多种转录因子。本研究首次完成唐古特大黄不同组织的转录组分析，可为解析蒽醌类生物合成相关基因、阐明唐古特大黄活性成分的分子调控机制提供重要支撑。