An organ-specific transcriptomic atlas of the medicinal plant Bletilla striata: Protein-coding genes, microRNAs, and regulatory networks.

As one of the important species belonging to the Bletilla genus of Orchidaceae, Bletilla striata (Thunb.) Rchb. f., possesses both ornamental and medicinal values. Its dried tubers are used as a traditional Chinese medicine, and several secondary metabolites have been indicated to be the active ingredients. However, the molecular mechanisms related to the regulation of secondary metabolism have not been characterized in B. striata. In this study, integrated analysis of RNA sequencing (RNA-seq), small RNA sequencing (sRNA-seq), and degradome sequencing (degradome-seq) data from three organs (leaf, root, and tuber) of B. striata provided us with a comprehensive view of the microRNA (miRNA)-mediated regulatory network. Firstly, based on the RNA-seq data, the organ-specific expression patterns of the protein-coding genes, especially for those related to secondary metabolism, were investigated. Secondly, 342 conserved miRNA candidates were identified from B. striata. These miRNAs were assigned to 88 families, some of which were selected for expression pattern analysis. Additionally, 31 hairpin-structured precursors encoding 23 novel miRNAs were uncovered from the transcriptome assembly. Thirdly, based on the degradome signatures, 1,142 validated miRNA-target pairs (involving 167 conserved miRNAs and six novel miRNAs and 51 target genes) were included in the regulatory network. Organ-specific expression level comparison between the miRNAs and their targets revealed some interesting miRNA-target pairs. Fourthly, some valuable subnetworks were extracted for further functional studies. Additionally, some regulatory pathways were indicated to be monocot specific. Summarily, our results lay a solid basis for in-depth studies on the regulatory mechanisms underlying the production of the medicinal ingredients in B. striata.

RNA-, sRNA-, and degradome-seq were performed for three organs of B. striata. Organ-specific expression patterns of the protein-coding genes were analyzed. A total of 365 miRNAs were identified and subject to expression pattern analysis. A total of 1,142 miRNA-target pairs were validated for network construction. Some miRNA-mediated regulatory pathways were indicated to be monocot specific.

Organ-specific, integrated omics data-based study on the metabolic pathways of the medicinal plant Bletilla striata (Orchidaceae).

BACKGROUND: Bletilla striata is one of the important species belonging to the Bletilla genus of Orchidaceae. Since its extracts have an astringent effect on human tissues, B. striata is widely used for hemostasis and healing. Recently, some other beneficial effects have also been uncovered, such as antioxidation, antiinflammation, antifibrotic, and immunomodulatory activities. As a key step towards a thorough understanding on the medicinal ingredient production in B. striata, deciphering the regulatory codes of the metabolic pathways becomes a major task. RESULTS: In this study, three organs (roots, tubers and leaves) of B. striata were analyzed by integrating transcriptome sequencing and untargeted metabolic profiling data. Five different metabolic pathways, involved in polysaccharide, sterol, flavonoid, terpenoid and alkaloid biosynthesis, were investigated respectively. For each pathway, the expression patterns of the enzyme-coding genes and the accumulation levels of the metabolic intermediates were presented in an organ-specific way. Furthermore, the relationships between enzyme activities and the levels of the related metabolites were partially inferred. Within the biosynthetic pathways of polysaccharides and flavonoids, long-range phytochemical transportation was proposed for certain metabolic intermediates and/or the enzymes. CONCLUSIONS: The data presented by this work could strengthen the molecular basis for further studies on breeding and medicinal uses of B. striata.

Bioinformatics-assisted, integrated omics studies on medicinal plants.

The immense therapeutic and economic values of medicinal plants have attracted increasing attention from the worldwide researchers. It has been recognized that production of the authentic and high-quality herbal drugs became the prerequisite for maintaining the healthy development of the traditional medicine industry. To this end, intensive research efforts have been devoted to the basic studies, in order to pave a way for standardized authentication of the plant materials, and bioengineering of the metabolic pathways in the medicinal plants. In this paper, the recent advances of omics studies on the medicinal plants were summarized from several aspects, including phenomics and taxonomics, genomics, transcriptomics, proteomics and metabolomics. We proposed a multi-omics data-based workflow for medicinal plant research. It was emphasized that integration of the omics data was important for plant authentication and mechanistic studies on plant metabolism. Additionally, the computational tools for proper storage, efficient processing and high-throughput analyses of the omics data have been introduced into the workflow. According to the workflow, authentication of the medicinal plant materials should not only be performed at the phenomics level but also be implemented by genomic and metabolomic marker-based examination. On the other hand, functional genomics studies, transcriptional regulatory networks and protein-protein interactions will contribute greatly for deciphering the secondary metabolic pathways. Finally, we hope that our work could inspire further efforts on the bioinformatics-assisted, integrated omics studies on the medicinal plants.

MepmiRDB: a medicinal plant microRNA database.

MicroRNAs (miRNAs) have been recognized as a key regulator in plant development and metabolism. Recent reports showed that the miRNAs of medicinal plants not only act as a critical modulator in secondary metabolism but also had a great potential of performing cross-kingdom gene regulation. Although several plant miRNA repositories have been publicly available, no miRNA database specific for medicinal plants has been reported to date. Here, we report the first version of MepmiRDB (medicinal plant microRNA database), which is freely accessible at http://mepmirdb.cn/mepmirdb/index.html. This database accommodates thousands of miRNA candidates belonging to 29 medicinal plant species. The miRNA information on sequences, expression patterns and regulatory networks has been included in the functional modules of the database. Specifically, the 'Sequence' module provides the sequences of the mature miRNAs and their precursors, and the structure information of the precursors. Moreover, the processing and small RNA accumulation signals on the miRNA precursors are also included in the 'Sequence' module. The organ/growth condition-specific expression information of the mature miRNAs has been stored in the 'Expression' module. The 'Interaction' module offers the information of the degradome-validated miRNA-target pairs of eight plant species. The 'Search' module enables users to search for the miRNAs by plant species and miRNA families, or by sequences. All data in this database are available for download. Taken together, the functional modules of MepmiRDB ensure its importance and timeliness for mechanistic and functional studies on the medicinal plant miRNAs.

Transcriptome-wide identification of microRNAs and functional insights inferred from microRNA-target pairs in Physalis angulata L.

Physalis angulata L., a member of the family Solanaceae, is widely used as the folk medicine in various countries. Continuous research efforts are devoted to the discovery of the effective medicinal ingredients from Physalis angulata. However, due to the limited resources of genome and transcriptome sequencing data, only a few studies have been performed at the gene regulatory level. In this study, the transcriptomes of five organs (roots, stems, leaves, flowers and fruits) of Physalis angulata were reported. Based on the transcriptome assembly containing 196,117 unique transcripts, a total of 17,556 SSRs (simple sequence repeats) were identified, which could be useful RNA-based barcoding for discrimination of the plants closely relative to Physalis angulata. Additionally, 24 transcripts were discovered to be the potential microRNA (miRNA) precursors which encode a total of 31 distinct mature miRNAs. Some of these precursors showed organ-specific expression patterns. Target prediction revealed 116 miRNA-target pairs, involving 31 miRNAs and 83 target transcripts in Physalis angulata. Taken together, our results could serve as the data resource for in-depth studies on the molecular regulatory mechanisms related to the production of medicinal ingredients in Physalis angulata.

A transcriptome-wide, organ-specific regulatory map of Dendrobium officinale, an important traditional Chinese orchid herb.

Dendrobium officinale is an important traditional Chinese herb. Here, we did a transcriptome-wide, organ-specific study on this valuable plant by combining RNA, small RNA (sRNA) and degradome sequencing. RNA sequencing of four organs (flower, root, leaf and stem) of Dendrobium officinale enabled us to obtain 536,558 assembled transcripts, from which 2,645, 256, 42 and 54 were identified to be highly expressed in the four organs respectively. Based on sRNA sequencing, 2,038, 2, 21 and 24 sRNAs were identified to be specifically accumulated in the four organs respectively. A total of 1,047 mature microRNA (miRNA) candidates were detected. Based on secondary structure predictions and sequencing, tens of potential miRNA precursors were identified from the assembled transcripts. Interestingly, phase-distributed sRNAs with degradome-based processing evidences were discovered on the long-stem structures of two precursors. Target identification was performed for the 1,047 miRNA candidates, resulting in the discovery of 1,257 miRNA--target pairs. Finally, some biological meaningful subnetworks involving hormone signaling, development, secondary metabolism and Argonaute 1-related regulation were established. All of the sequencing data sets are available at NCBI Sequence Read Archive (http://www.ncbi.nlm.nih.gov/sra/). Summarily, our study provides a valuable resource for the in-depth molecular and functional studies on this important Chinese orchid herb.