Glycyrrhiza uralensis transcriptome landscape and study of phytochemicals

Medicinal and industrial properties of phytochemicals (eq., glycyrrhizin) from the root of Glycyrrhiza uralensis (licorice plant) made it an attractive, multimillion-dollar trade item. Bioengineering of plants is one of the solutions to answer such high market demand and to prevent plants from the extinction. Unfortunately limited genomic information on medicinal plants restricts their research and thus biosynthetic mechanisms of many important phytochemicals are still poorly understood. In this work we leveraged the power of de-novo (no reference genome sequence available) assembly of Illumina RNA-seq data to study the transcriptome of the licorice plant. Our analysis is based on sequencing results of libraries made from samples that belonged to different tissues (root an leaf) and were collected at different seasons and from two slightly distinct strains (glycyrrhizin low and high producing strain). We provide functional annotations and the expression profile of 43,882 assembled unigenes, which are suitable for various further studies. Here, we searched for Glycyrrhiza uarlensis specific enzymes involved in isoflavonoid biosynthesis as well as elucidated putative Cytochrome P450 (CYP) enzymes and putative vacuolar saponin transporters involved in glycyrrhizin production in the licorice root. To disseminate the data and the analysis results we constructed publicly available the Glycyrrhiza uralensis database. This work will contribute to a better understanding of the secondary metabolites biosynthetic pathways in licorice plants, and possibly in other medicinal plants, and will provide an important resource to further advance transcriptomics studies in legumes.

乌拉尔甘草（Glycyrrhiza uralensis，俗称甘草）根部所含植物化学物（例如甘草酸（glycyrrhizin））兼具药用与工业价值，使其成为市值数百万美元的热门贸易商品。为满足高昂的市场需求并避免该物种走向灭绝，植物生物工程是可行的解决方案之一。遗憾的是，药用植物的基因组信息匮乏，限制了相关研究推进，因此诸多重要植物化学物的生物合成机制仍未得到充分阐明。本研究依托Illumina RNA测序数据的从头组装（无参考基因组序列可用）技术，对甘草的转录组（transcriptome）展开研究。分析所用的测序文库来自不同组织（根与叶）的样本，这些样本采集自不同季节，且来源于两个略有差异的菌株：低甘草酸生产菌株与高甘草酸生产菌株。本研究共组装得到43882条单基因（Unigene）序列，并为其提供了功能注释与表达谱信息，可支撑各类后续研究工作。在此基础上，我们筛选了参与异黄酮生物合成的乌拉尔甘草特异性酶类，并阐明了参与甘草根部甘草酸合成的推定细胞色素P450（Cytochrome P450，CYP）酶类以及推定的液泡皂苷转运蛋白。为公开传播本研究的数据与分析结果，我们搭建了可公开获取的乌拉尔甘草数据库。本研究有助于更深入地理解甘草乃至其他药用植物的次生代谢物生物合成途径，并为豆科植物的转录组学后续研究提供重要的基础资源。