The roots of Stephania tetrandra are used as a traditional Chinese medicine. Isoquinoline alkaloids are considered to be the most important and effective components in this herb, but little is known about the molecular mechanism underlying their biosynthesis. In this context, this study aimed to reveal candidate genes related to isoquinoline alkaloid biosynthesis in S. tetrandra. Determination of tetrandrine and fangchinoline in the roots and leaves of S. tetrandra by HPLC showed that the roots had much higher contents of the two isoquinoline alkaloids than the leaves. Thus, a comparative transcriptome analysis of the two tissues was performed to uncover candidate genes involved in isoquinoline alkaloid biosynthesis. A total of 71 674 unigenes was obtained and 31 994 of these were assigned putative functions based on BLAST searches against 6 annotation databases. Among the 79 isoquinoline alkaloid-related unigenes, 51 were differentially expressed, with 42 and 9 genes upregulated and downregulated, respectively, when the roots were compared with the leaves. The upregulated differentially expressed genes were consistent with isoquinoline alkaloid accumulation in roots and thus were deemed key candidate genes for isoquinoline alkaloid biosynthesis in the roots. Moreover, the expression profiles of 10 isoquinoline alkaloid-related differentially expressed genes between roots and leaves were validated by quantitative real-time polymerase chain reaction, which indicated that our transcriptome and gene expression profiles were reliable. This study not only provides a valuable genomic resource for S. tetrandra but also proposes candidate genes involved in isoquinoline alkaloid biosynthesis and transcription factors related to the regulation of isoquinoline alkaloid biosynthesis. The results lay a foundation for further studies on isoquinoline alkaloid biosynthesis in this medicinal plant.

中文翻译：

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比较转录组分析揭示了参与黄芪异喹啉生物碱生物合成的候选基因

Stephania tandra 的根被用作中药。异喹啉生物碱被认为是这种草药中最重要和最有效的成分，但对其生物合成的分子机制知之甚少。在此背景下，本研究旨在揭示与防毒粉虱中异喹啉生物碱生物合成相关的候选基因。高效液相色谱法测定粉防己根和叶中的粉防己碱和防己碱表明，根中两种异喹啉生物碱的含量远高于叶。因此，对两种组织进行了比较转录组分析，以揭示参与异喹啉生物碱生物合成的候选基因。总共获得了 71 674 个 unigenes，其中 31 994 个被分配了基于对 6 个注释数据库的 BLAST 搜索的假定功能。在79个异喹啉生物碱相关unigenes中，51个差异表达，42个基因和9个基因分别上调和下调，当比较根和叶时。上调的差异表达基因与根中异喹啉生物碱的积累一致，因此被认为是根中异喹啉生物碱生物合成的关键候选基因。此外，通过定量实时聚合酶链反应验证了 10 个异喹啉生物碱相关差异表达基因在根和叶之间的表达谱，这表明我们的转录组和基因表达谱是可靠的。本研究不仅为粉防菌提供了宝贵的基因组资源，还提出了参与异喹啉生物碱生物合成的候选基因和与异喹啉生物碱生物合成调控相关的转录因子。该结果为进一步研究该药用植物中异喹啉生物碱的生物合成奠定了基础。