De novo sequencing and characterization of Picrorhiza kurrooa transcriptome at two temperatures showed major transcriptome adjustments

Transcriptomic and metabolomic profiling reveals the drought tolerance mechanism of Illicium difengpi (Schisandraceae)

Illicium difengpi (Schisandraceae), an endangered medicinal plant endemic to karst areas, is highly tolerant to drought and thus can be used as an ideal material for investigating adaptive mechanism to drought stress. The understanding of the drought tolerance of I. difengpi, especially at the molecular level, is lacking. In the present study, we aimed to clarify the molecular mechanism underlying drought tolerance in endemic I. difengpi plant in karst regions. The response characteristics of transcripts and changes in metabolite abundance of I. difengpi subjected to drought and rehydration were analyzed, the genes and key metabolites responsive to drought and rehydration were screened, and some important biosynthetic and secondary metabolic pathways were identified. A total of 231,784 genes and 632 metabolites were obtained from transcriptome and metabolome analyses, and most of the physiological metabolism in drought-treated I. difengpi plants recovered after rehydration. There were more upregulated genes than downregulated genes under drought and rehydration treatments, and rehydration treatment induced stable expression of 65.25% of genes, indicating that rehydration alleviated drought stress to some extent. Drought and rehydration treatment generated flavonoids, phenolic acids, flavonols, amino acids and their derivatives, as well as metabolites such as saccharides and alcohols in the leaves of I. difengpi plants, which alleviated the injury caused by excessive reactive oxygen species. The integration of transcriptome and metabolome analyses showed that, under drought stress, I. difengpi increased glutathione, flavonoids, polyamines, soluble sugars and amino acids, contributing to cell osmotic potential and antioxidant activity. The results show that the high drought tolerance and recovery after rehydration are the reasons for the normal growth of I. difengpi in karst mountain areas.

Bio Prospecting of Endophytes and PGPRs in Artemisinin Production for the Socio-economic Advancement

The growing demand for Artemisia annua plants in healthcare, food, and pharmaceutical industries has led to increased cultivation efforts to extract a vital compound, Artemisinin. The efficacy of Artemisinin as a potent drug against malaria disease is well established but its limited natural abundance. However, the common practice of using chemical fertilizers for maximum yield has adverse effects on plant growth, development, and the quality of phytochemicals. To address these issues, the review discusses the alternative approach of harnessing beneficial rhizosphere microbiota, particularly plant growth-promoting rhizobacteria (PGPR). Microbes hold substantial biotechnological potential for augmenting medicinal plant production, offering an environmentally friendly and cost-effective means to enhance medicinal plant production. This review article aims to identify a suitable endophytic population capable of enabling Artemisia sp. to thrive amidst abiotic stress while simultaneously enhancing Artemisinin production, thereby broadening its availability to a larger population. Furthermore, by subjecting endophytes to diverse combinations of harsh conditions, this review sheds light on the modulation of essential artemisinin biosynthesis pathway genes, both up regulated and down regulated. The collective findings suggest that through the in vitro engineering of endophytic communities and their in vivo application to Artemisia plants cultivated in tribal population fields, artemisinin production can be significantly augmented. The overall aim of this review to explore the potential of harnessing microbial communities, their functions, and services to enhance the cultivation of medicinal plants. It outlines a promising path toward bolstering artemisinin production, which holds immense promise in the fight against malaria.

Transcriptome and metabolome profiling of the medicinal plant Veratrum mengtzeanum reveal key components of the alkaloid biosynthesis

Veratrum mengtzeanum is the main ingredient for Chinese folk medicine known as "Pimacao" due to its unique alkaloids. A diverse class of plant-specific metabolites having key pharmacological activities. There are limited studies on alkaloid synthesis and its metabolic pathways in plants. To elucidate the alkaloid pathway and identify novel biosynthetic enzymes and compounds in V. mengtzeanum, transcriptome and metabolome profiling has been conducted in leaves and roots. The transcriptome of V. mengtzeanum leaves and roots yielded 190,161 unigenes, of which 33,942 genes expressed differentially (DEGs) in both tissues. Three enriched regulatory pathways (isoquinoline alkaloid biosynthesis, indole alkaloid biosynthesis and tropane, piperidine and pyridine alkaloid biosynthesis) and a considerable number of genes such as AED3-like, A4U43, 21 kDa protein-like, 3-O-glycotransferase 2-like, AtDIR19, MST4, CASP-like protein 1D1 were discovered in association with the biosynthesis of alkaloids in leaves and roots. Some transcription factor families, i.e., AP2/ERF, GRAS, NAC, bHLH, MYB-related, C3H, FARI, WRKY, HB-HD-ZIP, C2H2, and bZIP were also found to have a prominent role in regulating the synthesis of alkaloids and steroidal alkaloids in the leaves and roots of V. mengtzeanum. The metabolome analysis revealed 74 significantly accumulated metabolites, with 55 differentially accumulated in leaves compared to root tissues. Out of 74 metabolites, 18 alkaloids were highly accumulated in the roots. A novel alkaloid compound viz; 3-Vanilloylygadenine was discovered in root samples. Conjoint analysis of transcriptome and metabolome studies has also highlighted potential genes involved in regulation and transport of alkaloid compounds. Here, we have presented a comprehensive metabolic and transcriptome profiling of V. mengtzeanum tissues. In earlier reports, only the roots were reported as a rich source of alkaloid biosynthesis, but the current findings revealed both leaves and roots as significant manufacturing factories for alkaloid biosynthesis.

Iridoid glycosides from Picrorhiza genus endemic to the Himalayan region: phytochemistry, biosynthesis, pharmacological potential and biotechnological intercessions to boost production

Iridoid glycosides are monoterpenoids synthesized in several plant species known to exhibit a diverse range of pharmacological activities. They are used as important bioactive ingredients in many commercially available drug formulations and as lead compounds in pharmaceutical research. The genus Picrorhiza comprises two medicinally important herbs endemic to the Himalayan region viz. Picrorhiza kurrooa Royle and Picrorhiza scrophulariiflora Hong. The medicinal properties of these two species are mainly due to iridoid glycosides present in their root, rhizome, and leaves. Unregulated harvesting from the wild, habitat specificity, narrow distribution range, small population size and lack of organized cultivation led to the enrolling of these species in the endangered category by the International Union for Conservation of Nature and Natural Resources (IUCN). Therefore, there is a need for immediate biotechnological and molecular interventions. Such intercessions will open up new vistas for large-scale propagation, development of genomic/transcriptomic resources for understanding the biosynthetic pathway, the possibility of genetic/metabolic manipulations, and possible commercialization of iridoid glycosides. The current review article elucidates the phytochemistry and pharmacological importance of iridoid glycosides from the genus Picrorhiza. In addition, the role of biotechnological approaches and opportunities offered by next-generation sequencing technologies in overcoming challenges associated with the genetic engineering of these species are also discussed.

Transcriptome and Metabolome Analysis of the Synthesis Pathways of Allelochemicals in Eupatorium adenophorum

Eupatorium adenophorum (Crofton weed) is an invasive weed in more than 30 countries. It inhibits the growth of surrounding plants by releasing allelochemicals during its invasion. However, the synthetic pathways and molecular mechanisms of its allelochemicals have been rarely reported. In this study, the related genes and pathways of allelochemicals in E. adenophorum were analyzed. Transcriptome analysis showed that differentially expressed genes (DEGs) were mainly enriched in the phenylpropanoid biosynthetic pathway and flavonoid biosynthetic pathway. Thirty-three DEGs involved in the synthesis of allelochemicals were identified, and 30 DEGs showed significant differences in blades and stems. Six allelochemicals were identified from blades and stems by ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Correlation analysis of genes and metabolites showed a strong correlation between the five genes and allelochemicals. In addition, this study supplemented the biosynthetic pathway of Eupatorium adenophorum B (HHO). It was found that acyclic sesquiterpene synthase (NES), δ-cadinene synthase (TPS), and cytochrome P450 (P450) were involved in the synthesis of HHO. These findings provide a dynamic spectrum consisting of allelochemical metabolism and a coexpression network of allelochemical synthesis genes in E. adenophorum.

Comparative transcriptomic analysis and antioxidant defense mechanisms in clusterbean (Cyamopsis tetragonoloba (L.) Taub.) genotypes with contrasting drought tolerance

To understand drought tolerance mechanism(s) in clusterbean (Cyamopsis tetragonoloba), we conducted physiological, biochemical, and de novo comparative transcriptome analysis of drought-tolerant (RGC-1002) and drought-sensitive (RGC-1066) genotypes subjected to 30 days of drought stress. Relative water content (RWC) was maintained in tolerant genotype but was reduced in sensitive genotype. Leaf pigment concentrations were higher in tolerant genotype. Net photosynthesis was significantly decreased in sensitive genotype but insignificant reduction was found in tolerant genotype. Enzymatic antioxidant (GR, APX, DHAR) activities were enhanced in tolerant genotype, while there were insignificant changes in these enzymes in sensitive genotype. The ratios of antioxidant molecules (ASC/DHA and GSH/GSSG) were higher in tolerant genotype as compared to sensitive genotype. In sensitive genotype, 6625 differentially expressed genes (DEGs) were upregulated and 5365 genes were downregulated. In tolerant genotype, 5206 genes were upregulated and 2793 genes were downregulated. In tolerant genotype, transketolase family protein, phosphoenolpyruvate carboxylase 3, temperature-induced lipocalin, and cytochrome oxidase were highly upregulated. Moreover, according to Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, the drought tolerance may be attributed to upregulated starch and sucrose metabolism-related genes in tolerant genotype. Finally, quantitative real-time PCR confirmed the reproducibility of the RNA-seq data.

miRbiom: Machine-learning on Bayesian causal nets of RBP-miRNA interactions successfully predicts miRNA profiles

Formation of mature miRNAs and their expression is a highly controlled process. It is very much dependent upon the post-transcriptional regulatory events. Recent findings suggest that several RNA binding proteins beyond Drosha/Dicer are involved in the processing of miRNAs. Deciphering of conditional networks for these RBP-miRNA interactions may help to reason the spatio-temporal nature of miRNAs which can also be used to predict miRNA profiles. In this direction, >25TB of data from different platforms were studied (CLIP-seq/RNA-seq/miRNA-seq) to develop Bayesian causal networks capable of reasoning miRNA biogenesis. The networks ably explained the miRNA formation when tested across a large number of conditions and experimentally validated data. The networks were modeled into an XGBoost machine learning system where expression information of the network components was found capable to quantitatively explain the miRNAs formation levels and their profiles. The models were developed for 1,204 human miRNAs whose accurate expression level could be detected directly from the RNA-seq data alone without any need of doing separate miRNA profiling experiments like miRNA-seq or arrays. A first of its kind, miRbiom performed consistently well with high average accuracy (91%) when tested across a large number of experimentally established data from several conditions. It has been implemented as an interactive open access web-server where besides finding the profiles of miRNAs, their downstream functional analysis can also be done. miRbiom will help to get an accurate prediction of human miRNAs profiles in the absence of profiling experiments and will be an asset for regulatory research areas. The study also shows the importance of having RBP interaction information in better understanding the miRNAs and their functional projectiles where it also lays the foundation of such studies and software in future.

Transcriptome repository of North-Western Himalayan endangered medicinal herbs: a paramount approach illuminating molecular perspective of phytoactive molecules and secondary metabolism

Medicinal plants of the North-Western Himalayan region are known for their unprecedented biodiversity and valuable secondary metabolites that are unique to this dynamic geo-climatic region. From ancient times these medicinal herbs have been used traditionally for their therapeutic potentials. But from the last 2 decades increasing pharmaceutical demand, illegal and unorganized trade of these medicinal plants have accelerated the rate of over-exploitation in a non-scientific manner. In addition, climate change and anthropogenic activities also affected their natural habitat and driving most of these endemic plant species to critically endangered that foresee peril of mass extinction from this eco-region. Hence there is an urgent need for developing alternative sustainable approaches and policies to utilize this natural bioresource ensuring simultaneous conservation. Hither, arise the advent of sequencing-based transcriptomic studies significantly contributes to better understand the background of important metabolic pathways and related genes/enzymes of high-value medicinal herbs, in the absence of genomic information. The use of comparative transcriptomics in conjunction with biochemical techniques in North-Western Himalayan medicinal plants has resulted in significant advances in the identification of the molecular players involved in the production of secondary metabolic pathways over the last decade. This information could be used to further engineer metabolic pathways and breeding programs, ultimately leading to the development of in vitro systems dedicated to the production of pharmaceutically important secondary metabolites at the industrial level. Collectively, successful adoption of these approaches can certainly ensure the sustainable utilization of Himalayan bioresource by reducing the pressure on the wild population of these critically endangered medicinal herbs. This review provides novel insight as a transcriptome-based bioresource repository for the understanding of important secondary metabolic pathways genes/enzymes and metabolism of endangered high-value North-Western Himalayan medicinal herbs, so that researchers across the globe can effectively utilize this information for devising effective strategies for the production of pharmaceutically important compounds and their scale-up for sustainable usage and take a step forward in omics-based conservation genetics.

The first draft genome of Picrorhiza kurrooa, an endangered medicinal herb from Himalayas

Picrorhiza kurrooa is an endangered medicinal herb which is distributed across the Himalayan region at an altitude between 3000–5000 m above mean sea level. The medicinal properties of P. kurrooa are attributed to monoterpenoid picrosides present in leaf, rhizome and root of the plant. However, no genomic information is currently available for P. kurrooa, which limits our understanding about its molecular systems and associated responses. The present study brings the first assembled draft genome of P. kurrooa by using 227 Gb of raw data generated by Illumina and PacBio RS II sequencing platforms. The assembled genome has a size of n = ~ 1.7 Gb with 12,924 scaffolds. Four pronged assembly quality validations studies, including experimentally reported ESTs mapping and directed sequencing of the assembled contigs, confirmed high reliability of the assembly. About 76% of the genome is covered by complex repeats alone. Annotation revealed 24,798 protein coding and 9789 non-coding genes. Using the assembled genome, a total of 710 miRNAs were discovered, many of which were found responsible for molecular response against temperature changes. The miRNAs and targets were validated experimentally. The availability of draft genome sequence will aid in genetic improvement and conservation of P. kurrooa. Also, this study provided an efficient approach for assembling complex genomes while dealing with repeats when regular assemblers failed to progress due to repeats.

Comparative transcriptome analysis of Rheum australe, an endangered medicinal herb, growing in its natural habitat and those grown in controlled growth chambers

Rheum australe is an endangered medicinal herb of high altitude alpine region of Himalayas and is known to possess anti-cancerous properties. Unlike many herbs of the region, R. australe has broad leaves. The species thrives well under the environmental extremes in its niche habitat, therefore an understanding of transcriptome of R. australe to environmental cues was of significance. Since, temperature is one of the major environmental variables in the niche of R. australe, transcriptome was studied in the species growing in natural habitat and those grown in growth chambers maintained at 4 °C and 25 °C to understand genes associated with different temperatures. A total of 39,136 primarily assembled transcripts were obtained from 10,17,74,336 clean read, and 21,303 unigenes could match to public databases. An analysis of transcriptome by fragments per kilobase of transcript per million, followed by validation through qRT-PCR showed 22.4% up- and 22.5% down-regulated common differentially expressed genes in the species growing under natural habitat and at 4 °C as compared to those at 25 °C. These genes largely belonged to signaling pathway, transporters, secondary metabolites, phytohormones, and those associated with cellular protection, suggesting their importance in imparting adaptive advantage to R. australe in its niche.

Novel ASR isolated from drought stress responsive SSH library in pearl millet confers multiple abiotic stress tolerance in PgASR3 transgenic Arabidopsis

A genomic resource of drought stress responsive genes/ESTs was generated using Suppression Subtractive Hybridization (SSH) approach in a drought stress tolerant Pennisetum glaucum genotype 841B. Fifty five days old plants were subjected to drought stress after withholding water for different time intervals (10 days, 15 days, 20 days and 25 days). A forward subtractive cDNA library was prepared from isolated RNA of leaf tissue. Differential gene expression under drought stress was validated for selected nine contigs by RT-qPCR. A transcript homologous to Setaria italica ASR3 upregulated under drought stress was isolated from genotype 841B and characterized. Heterologous expression of PgASR3 was validated in Arabidopsis and confirmed under multiple abiotic stress conditions. A total of four independent transgenic lines overexpressing gene PgASR3 were analyzed by Southern blot at T₁ stage. For drought stress tolerance, three independent lines (T₂ stage) were analyzed by biochemical and physiological assays at seedling stage. The growth rate (shoot and root length) of transgenic seedlings improved as compared to WT seedling under differenct abiotic stress conditions. The three transgenic lines were also validated for drought stress tolerance and RT-qPCR analysis, at maturity stage. Under drought stress conditions, the mature transgenic lines showed higher levels of RWC, chlorophyll and proline but lower levels of MDA as compared to WT plants. PgASR3 gene isolated and validated in this study can be utilized for developing abiotic stress tolerant crops.

Comparative transcriptome analysis of root, stem, and leaf tissues of Entada phaseoloides reveals potential genes involved in triterpenoid saponin biosynthesis

Background

Entada phaseoloides (L.) Merr. is an important traditional medicinal plant. The stem of Entada phaseoloides is popularly used as traditional medicine because of its significance in dispelling wind and dampness and remarkable anti-inflammatory activities. Triterpenoid saponins are the major bioactive compounds of Entada phaseoloides. However, genomic or transcriptomic technologies have not been used to study the triterpenoid saponin biosynthetic pathway in this plant.

Results

We performed comparative transcriptome analysis of the root, stem, and leaf tissues of Entada phaseoloides with three independent biological replicates and obtained a total of 53.26 Gb clean data and 116,910 unigenes, with an average N50 length of 1218 bp. Putative functions could be annotated to 42,191 unigenes (36.1%) based on BLASTx searches against the Non-redundant, Uniprot, KEGG, Pfam, GO, KEGG and COG databases. Most of the unigenes related to triterpenoid saponin backbone biosynthesis were specifically upregulated in the stem. A total of 26 cytochrome P450 and 17 uridine diphosphate glycosyltransferase candidate genes related to triterpenoid saponin biosynthesis were identified. The differential expressions of selected genes were further verified by qPT-PCR.

Conclusions

The dataset reported here will facilitate the research about the functional genomics of triterpenoid saponin biosynthesis and genetic engineering of Entada phaseoloides.

PkGPPS.SSU interacts with two PkGGPPS to form heteromeric GPPS in Picrorhiza kurrooa: Molecular insights into the picroside biosynthetic pathway

Geranyl geranyl pyrophosphate synthase (GGPPS) is known to form an integral subunit of the heteromeric GPPS (geranyl pyrophosphate synthase) complex and catalyzes the biosynthesis of monoterpene in plants. Picrorhiza kurrooa Royle ex Benth., a medicinally important high altitude plant is known for picroside biomolecules, the monoterpenoids. However, the significance of heteromeric GPPS in P. kurrooa still remains obscure. Here, transient silencing of PkGGPPS was observed to reduce picroside-I (P-I) content by more than 60% as well as picroside-II (P-II) by more than 75%. Thus, PkGGPPS was found to be involved in the biosynthesis of P-I and P-II besides other terpenoids. To unravel the mechanism, small subunit of GPPS (PkGPPS.SSU) was identified from P. kurrooa. Protein-protein interaction studies in yeast as well as bimolecular fluorescence complementation (BiFC) in planta have indicated that large subunit of GPPS PkGPPS.LSUs (PkGGPPS1 and PkGGPPS2) and PkGPPS.SSU form a heteromeric GPPS. Presence of similar conserved domains such as light responsive motifs, low temperature responsive elements (LTRE), dehydration responsive elements (DREs), W Box and MeJA responsive elements in the promoters of PkGPPS.LSU and PkGPPS.SSU documented their involvement in picroside biosynthesis. Further, the tissue specific transcript expression analysis vis-à-vis epigenetic regulation (DNA methylation) of promoters as well as coding regions of PkGPPS.LSU and PkGPPS.SSU has strongly suggested their role in picroside biosynthesis. Taken together, the newly identified PkGPPS.SSU formed the heteromeric GPPS by interacting with PkGPPS.LSUs to synthesize P-I and P-II in P. kurrooa.

Growth Kinetics, Metabolites Production and Expression Profiling of Picrosides Biosynthetic Pathway Genes in Friable Callus Culture of Picrorhiza kurroa Royle ex Benth

The rising demand for picrosides commercially and over-exploitation of Picrorhiza kurroa from natural habitat has to initiate alternative strategies for sustainable production of metabolites. In the present research, wild leaf explant of P. kurroa was used to produce friable callus under different culture condition, i.e., dark and light with two temperature variants (15 °C and 25 °C). Afterward, callus cell lines were screened based on growth biomass and metabolites content accumulation. The results revealed, maximum callus growth index along with antioxidant potential (IC₅₀-40.88 μg/mL) and total phenol content (41.35 μg/mg) were observed under dark 25 °C. However, under light 15 °C, highest accumulation of picroside II (0.58 μg/mg), cinnamic acid (0.15 μg/mg), p-hydroxy acetophenone (0.30 μg/mg), total flavonoids (77.30 μg/mg), nitrogen (7.06%), carbohydrates (18.03%), and protein (44.12%) were detected. Major reported metabolite in callus was picroside I (1.63 μg/mg) under dark 15 °C. For the first time, picroside III content (range 0.15-0.56 μg/mg) was also detected and quantified in leaf-derived calli. Expression profiling of picroside biosynthetic pathway genes showed a positive correlation with the observed metabolites. Furthermore, an optimized protocol of metabolites enriched callus biomass could be used as potential strategy for sustainable production of picrosides at commercial scale.

Two light responsive WRKY genes exhibit positive and negative correlation with picroside content in Picrorhiza kurrooa Royle ex Benth, an endangered medicinal herb

Picrorhiza kurrooa is an endangered herb known to produce the medicinally important picrosides through isoprenoid pathway. The present work showed the functionality of WRKY motifs (TGAC cis-acting elements) present in the promoters of regulatory genes 3-hydroxy-3-methylglutaryl coenzyme A reductase (Pkhmgr) and 1-deoxy-d-xylulose-5-phosphate synthase (Pkdxs) of the picrosides biosynthetic pathway by electrophoretic mobility shift assay. Also, the two WRKY genes, PkdWRKY and PksWRKY, were characterized and found to contain double and single characteristic WRKY domains, respectively along with a zinc-finger motif in each domain. Expression analysis revealed that PkdWRKY and PksWRKY exhibited a positive and negative correlation, respectively, with picrosides content under the environment of light and in different tissues. Functional evaluation in yeast showed DNA binding ability of both PksWRKY and PkdWRKY; however, only PkdWRKY exhibited transcriptional activation ability. Transient overexpression of PkdWRKY and PksWRKY in tobacco modulated the expression of selected native genes of tobacco involved in MVA and MEP pathway suggesting functionality of PkdWRKY and PksWRKY in planta. Collectively, data suggested that PkdWRKY and PksWRKY might be positive and negative regulators, respectively in the picrosides biosynthetic pathway.

De novo transcriptome provides insights into the growth behaviour and resveratrol and trans-stilbenes biosynthesis in Dactylorhiza hatagirea - An endangered alpine terrestrial orchid of western Himalaya

This is the first report on de novo transcriptome of Dactylorhiza hatagirea, a critically-endangered, terrestrial orchid of alpine Himalayas. The plant is acclaimed for medicinal properties but little is known about its secondary-metabolites profile or cues regulating their biosynthesis. De novo transcriptome analysis was therefore, undertaken to gain basic understanding on these aspects, while circumventing the acute limitation of plant material availability. 65,384 transcripts and finally, 37,371 unigenes were assembled de novo from a total of 236 million reads obtained from shoot, tuber and leaves of the plant. Dominance of differentially-expressing-genes (DEGs) related to cold-stress-response and plant-hormone-signal-transduction; and those involved in photosynthesis, sugar-metabolism and secondary-metabolite-synthesis provided insights into carbohydrate-partitioning in the plant during its preparation for freezing winter at natural habitat. DEGs of glucomannan, ascorbic acid, carotenoids, phylloquinone/naphthoquinones, indole alkaloids, resveratrol and stilbene biosynthesis revealed the secondary-metabolite profile of D. hatagirea. UHPLC results confirmed appreciable amounts of resveratrol and trans-stilbene in D. hatagirea tubers, for the first time. Expression analysis of 15 selected genes including those of phenylpropanoid pathway confirmed the validity of RNA-seq data. Opportunistic growth, temperature- and tissue-specific-differential-expression of secondary metabolite biosynthesis and stress tolerant genes were confirmed using clonal plants growing at 8, 15 and 25 °C.

Identification of candidate genes involved in steroidal alkaloids biosynthesis in organ-specific transcriptomes of Veratrum nigrum L

Veratrum nigrum is protected plant of Melanthiaceae family, able to synthetize unique steroidal alkaloids important for pharmacy. Transcriptomes from leaves, stems and rhizomes of in vitro maintained V. nigrum plants were sequenced and annotated for genes and markers discovery. Sequencing of samples derived from the different organs resulted in a total of 108,511 contigs with a mean length of 596 bp. Transcripts derived from leaf and stalk were annotated at 28%, and 38% in Nr nucleotide database, respectively. The sequencing revealed 949 unigenes related with lipid metabolism, including 73 transcripts involved in steroids and genus-specific steroid alkaloids biosynthesis. Additionally, 3203 candidate SSRs markers we identified in unigenes with average density of one SSR locus every 6.2 kb sequence. Unraveling of biochemical machinery of the pathway responsible for steroidal alkaloids will open possibility to design and optimize biotechnological process. The transcriptomic data provide valuable resources for biochemical, molecular genetics, comparative transcriptomics, functional genomics, ecological and evolutionary studies of V. nigrum.

De novo transcriptome sequencing and metabolite profiling analyses reveal the complex metabolic genes involved in the terpenoid biosynthesis in Blue Anise Sage (Salvia guaranitica L.)

Many terpenoid compounds have been extracted from different tissues of Salvia guaranitica. However, the molecular genetic basis of terpene biosynthesis pathways is virtually unknown. In this study, approximately 4 Gb of raw data were generated from the transcriptome of S. guaranitica leaves using Illumina HiSeq 2000 sequencing. After filtering and removing the adapter sequences from the raw data, the number of reads reached 32 million, comprising 186 million of high-quality nucleotide bases. A total of 61,400 unigenes were assembled de novo and annotated for establishing a valid database for studying terpenoid biosynthesis. We identified 267 unigenes that are putatively involved in terpenoid metabolism (including, 198 mevalonate and methyl-erythritol phosphate (MEP) pathways, terpenoid backbone biosynthesis genes and 69 terpene synthases genes). Moreover, three terpene synthase genes were studied for their functions in terpenoid biosynthesis by using transgenic Arabidopsis; most transgenic Arabidopsis plants expressing these terpene synthetic genes produced increased amounts of terpenoids compared with wild-type control. The combined data analyses from the transcriptome and metabolome provide new insights into our understanding of the complex metabolic genes in terpenoid-rich blue anise sage, and our study paves the way for the future metabolic engineering of the biosynthesis of useful terpene compounds in S. guaranitica.

Ocimum metabolomics in response to abiotic stresses: Cold, flood, drought and salinity

Ocimum tenuiflorum is a widely used medicinal plant since ancient times and still continues to be irreplaceable due to its properties. The plant has been explored chemically and pharmacologically, however, the molecular studies have been started lately. In an attempt to get a comprehensive overview of the abiotic stress response in O. tenuiflorum, de novo transcriptome sequencing of plant leaves under the cold, drought, flood and salinity stresses was carried out. A comparative differential gene expression (DGE) study was carried out between the common transcripts in each stress with respect to the control. KEGG pathway analysis and gene ontology (GO) enrichment studies exhibited several modifications in metabolic pathways as the result of four abiotic stresses. Besides this, a comparative metabolite profiling of stress and control samples was performed. Among the cold, drought, flood and salinity stresses, the plant was most susceptible to the cold stress. Severe treatments of all these abiotic stresses also decreased eugenol which is the main secondary metabolite present in the O. tenuiflorum plant. This investigation presents a comprehensive analysis of the abiotic stress effects in O. tenuiflorum. Current study provides an insight to the status of pathway genes’ expression that help synthesizing economically valuable phenylpropanoids and terpenoids related to the adaptation of the plant. This study identified several putative abiotic stress tolerant genes which can be utilized to either breed stress tolerant O. tenuiflorum through pyramiding or generating transgenic plants.

De Novo Transcriptome Assembly and Population Genetic Analyses for an Endangered Chinese Endemic Acer miaotaiense (Aceraceae)

Acer miaotaiense (P. C. Tsoong) is a rare and highly endangered plant in China. Because of the lack of genomic information and the limited number of available molecular markers, there are insufficient tools to determine the genetic diversity of this species. Here, 93,305 unigenes were obtained by multiple assembled contigs with a transcriptome sequencing program. Furthermore, 12,819 expressed sequence tag-derived simple sequence repeat (EST-SSR) markers were generated, 300 were randomly selected and synthesized, 19 primer pairs were identified as highly polymorphic (average number of alleles (N_a) = 8, expected heterozygosity (H_e) = 0.635, polymorphism information content (PIC) = 0.604) and were further used for population genetic analysis. All 261 samples were grouped into two genetic clusters by UPGMA, a principal component analyses and a STRUCTURE analyses. A moderate level of genetic differentiation (genetic differentiation index (F_st) = 0.059–0.116, gene flow = 1.904–3.993) among the populations and the major genetic variance (81.01%) within populations were revealed by the AMOVA. Based on the results, scientific conservation strategies should be established using in situ and ex situ conservation strategies. The study provides useful genetic information for the protection of precious wild resources and for further research on the origin and evolution of this endangered plant and its related species.

Transcriptome changes induced by abiotic stresses in Artemisia annua

Artemisia annua is known to be the source of artemisinin worldwide which is an antimalarial compound but is synthesised in very limited amount in the plant. Most research laid emphasis on the methods of enhancing artemisinin but our study has been planned in a way that it may simultaneously address two problems encountered by the plant. Firstly, to know the effect on the artemisinin content in the era of climate change because the secondary metabolites tend to increase under stress. Secondly, to identify some of the stress responsive genes that could help in stress tolerance of the plant under abiotic stress. Hence, the A. annua plants were subjected to four abiotic stresses (salt, cold, drought and water-logging) and it was observed that the artemisinin content increased in all the stress conditions except drought. Next, in order to identify the stress responsive genes, the transcriptome sequencing of the plants under stress was carried out resulting in 89,362 transcripts for control and 81,328, 76,337, 90,470 and 96,493 transcripts for salt, cold, drought, and water logging stresses. This investigation provides new insights for functional studies of genes involved in multiple abiotic stresses and potential candidate genes for multiple stress tolerance in A. annua.

Transcript profiling and gene expression analysis under drought stress in Ziziphus nummularia (Burm.f.) Wright & Arn

Drought is one of the prime abiotic stresses responsible for limiting agricultural productivity. A number of drought responsive genes have been isolated and functionally characterized but these studies have been restricted to a few model plant systems. Very few drought responsive genes have been reported till date from non model drought tolerant plants. The present study aimed at identifying differentially expressed genes from a drought tolerant, non-model plant, Ziziphus nummularia (Burm.f.) Wight & Arn. One month old seedlings of Z. nummularia were subjected to drought stress by 30% Polyethylene glycol (PEG 6000) treatment for 6, 12, 24, 48 and 72 h. A significant reduction in RWC and increase in proline was observed at 24 h and 48 h of treatment. Suppression subtractive hybridization (SSH) library was constructed with drought stressed seedlings after 24 h and 48 h of PEG 6000 treatment. A total of 142 and 530 unigenes from 24 h and 48 h library were identified respectively. Gene ontology studies revealed that about 9.78% and 15.07% unigenes from 24 h and 48 h SSH libraries were expressed in "response to stress". Fifteen putative drought responsive genes identified in SSH library were validated for drought responsive differential expression by RT-qPCR. Significant changes in fold expressions were observed with time in the treated samples compared to the control. A heat map revealing the expression profile of genes was constructed by hierarchical clustering. Various genes identified in SSH libraries can serve as a resource for marker discovery and selection of candidate genes to improve drought tolerance in other susceptible crops.

Transcriptome sequence analysis and mining of SSRs in Jhar Ber (Ziziphus nummularia (Burm.f.) Wight & Arn) under drought stress

Ziziphus nummularia (Burm.f.) Wight & Arn., a perennial shrub that thrives in the arid regions, is naturally tolerant to drought. However, there are limited studies on the genomics of drought tolerance in Ziziphus sp. In this study, RNA-sequencing of one month old seedlings treated with PEG 6000 was performed using Roche GS-FLX454 Titanium pyrosequencing. A total of 367,176 raw sequence reads were generated, and upon adapter trimming and quality filtration 351,872 reads were assembled de novo into 32,739 unigenes. Further characterization of the unigenes indicated that 73.25% had significant hits in the protein database. Kyoto encyclopedia of genes and genomes database (KEGG) identified 113 metabolic pathways from the obtained unigenes. A large number of drought-responsive genes were obtained and among them differential gene expression of 16 highly induced genes was validated by qRT-PCR analysis. To develop genic-markers, 3,425 simple sequence repeats (SSRs) were identified in 2,813 unigene sequences. The data generated shall serve as an important reservoir for the identification and characterization of drought stress responsive genes for development of drought tolerant crops.

Comparative transcriptomics uncovers differences in photoautotrophic versus photoheterotrophic modes of nutrition in relation to secondary metabolites biosynthesis in Swertia chirayita

Swertia chirayita is a high-value medicinal herb exhibiting antidiabetic, hepatoprotective, anticancer, antiediematogenic and antipyretic properties. Scarcity of its plant material has necessitated in vitro production of therapeutic metabolites; however, their yields were low compared to field grown plants. Possible reasons for this could be differences in physiological and biochemical processes between plants grown in photoautotrophic versus photoheterotrophic modes of nutrition. Comparative transcriptomes of S. chirayita were generated to decipher the crucial molecular components associated with the secondary metabolites biosynthesis. Illumina HiSeq sequencing yielded 57,460 and 43,702 transcripts for green house grown (SCFG) and tissue cultured (SCTC) plants, respectively. Biological role analysis (GO and COG assignments) revealed major differences in SCFG and SCTC transcriptomes. KEGG orthology mapped 351 and 341 transcripts onto secondary metabolites biosynthesis pathways for SCFG and SCTC transcriptomes, respectively. Nineteen out of 30 genes from primary metabolism showed higher in silico expression (FPKM) in SCFG versus SCTC, possibly indicating their involvement in regulating the central carbon pool. In silico data were validated by RT-qPCR using a set of 16 genes, wherein 10 genes showed similar expression pattern across both the methods. Comparative transcriptomes identified differentially expressed transcription factors and ABC-type transporters putatively associated with secondary metabolism in S. chirayita. Additionally, functional classification was performed using NCBI Biosystems database. This study identified the molecular components implicated in differential modes of nutrition (photoautotrophic vs. photoheterotrophic) in relation to secondary metabolites production in S. chirayita.

Transcriptome and metabolome profiling of Narcissus pseudonarcissus 'King Alfred' reveal components of Amaryllidaceae alkaloid metabolism

Amaryllidaceae alkaloids (AAs) represent a diverse class of plant specialized metabolites and many display potent pharmacological activities. The AA metabolic pathway is poorly understood and resources are minimal. To enable AA pathway elucidation and novel biosynthetic enzymes discovery, we generated comprehensive metabolomic and corresponding transcriptomic datasets from different tissues of Narcissus pseudonarcissus ‘King Alfred’. In this study, we performed untargeted UPLC-QTOF-MS metabolite analysis from different tissues, which generated exhaustive list of compounds, including several AAs, most predominant and diverse in bulbs. RNA sequencing of N. pseudonarcissus ‘King Alfred’ bulbs yielded 195,347 transcripts, after assembly. Top expressed genes belong to process like metabolism, survival, and defense including alkaloid biosynthetic genes. The transcriptome contained complete sequences for all proposed genes encoding AA-biosynthetic enzymes such as tyrosine decarboxylase (TYDC1 and TYDC2), phenylalanine ammonia-lyase (PAL1 and PAL2) and phenolic acids hydroxylases (C4H and C3H) to name a few. Furthermore, transcriptome data were validated using RT-qPCR analysis and expression study in different tissues of N. pseudonarcissus ‘King Alfred’ was performed. Here, we present the first comprehensive metabolome and transcriptome study from N. pseudonarcissus ‘King Alfred’ providing invaluable resources for metabolic engineering and biotechnological applications.

Transcriptome and metabolite analyses reveal the complex metabolic genes involved in volatile terpenoid biosynthesis in garden sage (Salvia officinalis)

A large number of terpenoid compounds have been extracted from different tissues of S. officinalis. However, the molecular genetic basis of terpene biosynthesis pathways is virtually unknown. In this study, approximately 6.6 Gb of raw data were generated from the transcriptome of S. officinalis leaves using Illumina HiSeq 2000 sequencing. After filtering and removing the adapter sequences from the raw data, the number of reads reached 21 million, comprising 98 million of high-quality nucleotide bases. 48,671 unigenes were assembled de novo and annotated for establishing a valid database for studying terpenoid biosynthesis. We identified 135 unigenes that are putatively involved in terpenoid metabolism, including 70 mevalonate and methyl-erythritol phosphate pathways, terpenoid backbone biosynthesis genes, and 65 terpene synthase genes. Moreover, five terpene synthase genes were studied for their functions in terpenoid biosynthesis by using transgenic tobacco; most transgenic tobacco plants expressing these terpene synthetic genes produced increased amounts of terpenoids compared with wild-type control. The combined data analyses from the transcriptome and metabolome provide new insights into our understanding of the complex metabolic genes in terpenoid-rich sage, and our study paves the way for the future metabolic engineering of the biosynthesis of useful terpene compounds in S. officinalis.

Population transcriptomic characterization of the genetic and expression variation of a candidate progenitor of Miscanthus energy crops

The use of transcriptome data in the study of the population genetics of a species can capture faint signals of both genetic variation and expression variation and can provide a broad picture of a species' genomic response to environmental conditions. In this study, we characterized the genetic and expression diversity of Miscanthus lutarioriparius by comparing more than 16,225 transcripts obtained from 78 individuals, belonging to 10 populations distributed across the species' entire geographic range. We only observed a low level of nucleotide diversity (π = 0.000434) among the transcriptome data of these populations, which is consistent with highly conserved sequences of functional elements and protein-coding genes captured with this method. Tests of population divergence using the transcriptome data were consistent with previous microsatellite data but proved to be more sensitive, particularly if gene expression variation was considered as well. For example, the analysis of expression data showed that genes involved in photosynthetic processes and responses to temperature or reactive oxygen species stimuli were significantly enriched in certain populations. This differential gene expression was primarily observed among populations and not within populations. Interestingly, nucleotide diversity was significantly negatively correlated with expression diversity within populations, while this correlation was positive among populations. This suggests that genetic and expression variation play separate roles in adaptation and population persistence. Combining analyses of genetic and gene expression variation represents a promising approach for studying the population genetics of wild species and may uncover both adaptive and nonadaptive processes.

Researches on Transcriptome Sequencing in the Study of Traditional Chinese Medicine

Due to its incomparable advantages, the application of transcriptome sequencing in the study of traditional Chinese medicine attracts more and more attention of researchers, which greatly promote the development of traditional Chinese medicine. In this paper, the applications of transcriptome sequencing in traditional Chinese medicine were summarized by reviewing recent related papers.

Comparative transcriptome analysis of shoot and root tissue of Bacopa monnieri identifies potential genes related to triterpenoid saponin biosynthesis

Background

Bacopa monnieri commonly known as Brahmi is utilized in Ayurveda to improve memory and many other human health benefits. Bacosides enriched standardized extract of Bacopa monnieri is being marketed as a memory enhancing agent. In spite of its well known pharmacological properties it is not much studied in terms of transcripts involved in biosynthetic pathway and its regulation that controls the secondary metabolic pathway in this plant. The aim of this study was to identify the potential transcripts and provide a framework of identified transcripts involved in bacosides production through transcriptome assembly.

Results

We performed comparative transcriptome analysis of shoot and root tissue of Bacopa monnieri in two independent biological replicate and obtained 22.48 million and 22.0 million high quality processed reads in shoot and root respectively. After de novo assembly and quantitative assessment total 26,412 genes got annotated in root and 18,500 genes annotated in shoot sample. Quality of raw reads was determined by using SeqQC-V2.2. Assembled sequences were annotated using BLASTX against public database such as NR or UniProt. Searching against the KEGG pathway database indicated that 37,918 unigenes from root and 35,130 unigenes from shoot were mapped to 133 KEGG pathways. Based on the DGE data we found that most of the transcript related to CYP450s and UDP-glucosyltransferases were specifically upregulated in shoot tissue as compared to root tissue. Finally, we have selected 43 transcripts related to secondary metabolism including transcription factor families which are differentially expressed in shoot and root tissues were validated by qRT-PCR and their expression level were monitored after MeJA treatment and wounding for 1, 3 and 5 h.

Conclusions

This study not only represents the first de novo transcriptome analysis of Bacopa monnieri but also provides information about the identification, expression and differential tissues specific distribution of transcripts related to triterpenoid sapogenin which is one of the most important pharmacologically active secondary metabolite present in Bacopa monnieri. The identified transcripts in this study will establish a foundation for future studies related to carrying out the metabolic engineering for increasing the bacosides biosynthesis and its regulation for human health benefits.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3865-5) contains supplementary material, which is available to authorized users.

Genome and Transcriptome sequence of Finger millet (Eleusine coracana (L.) Gaertn.) provides insights into drought tolerance and nutraceutical properties

Background

Finger millet (Eleusine coracana (L.) Gaertn.) is an important staple food crop widely grown in Africa and South Asia. Among the millets, finger millet has high amount of calcium, methionine, tryptophan, fiber, and sulphur containing amino acids. In addition, it has C4 photosynthetic carbon assimilation mechanism, which helps to utilize water and nitrogen efficiently under hot and arid conditions without severely affecting yield. Therefore, development and utilization of genomic resources for genetic improvement of this crop is immensely useful.

Results

Experimental results from whole genome sequencing and assembling process of ML-365 finger millet cultivar yielded 1196 Mb covering approximately 82% of total estimated genome size. Genome analysis showed the presence of 85,243 genes and one half of the genome is repetitive in nature. The finger millet genome was found to have higher colinearity with foxtail millet and rice as compared to other Poaceae species. Mining of simple sequence repeats (SSRs) yielded abundance of SSRs within the finger millet genome. Functional annotation and mining of transcription factors revealed finger millet genome harbors large number of drought tolerance related genes. Transcriptome analysis of low moisture stress and non-stress samples revealed the identification of several drought-induced candidate genes, which could be used in drought tolerance breeding.

Conclusions

This genome sequencing effort will strengthen plant breeders for allele discovery, genetic mapping, and identification of candidate genes for agronomically important traits. Availability of genomic resources of finger millet will enhance the novel breeding possibilities to address potential challenges of finger millet improvement.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3850-z) contains supplementary material, which is available to authorized users.

Detecting the Molecular System Signatures of Idiopathic Pulmonary Fibrosis through Integrated Genomic Analysis

Idiopathic Pulmonary Fibrosis (IPF) is an incurable progressive fibrotic disease of the lungs. We currently lack a systematic understanding of IPF biology and a systems approach may offer new therapeutic insights. Here, for the first time, a large volume of high throughput genomics data has been unified to derive the most common molecular signatures of IPF. A set of 39 differentially expressed genes (DEGs) was found critical to distinguish IPF. Using high confidence evidences and experimental data, system level networks for IPF were reconstructed, involving 737 DEGs found common across at least two independent studies. This all provided one of the most comprehensive molecular system views for IPF underlining the regulatory and molecular consequences associated. 56 pathways crosstalks were identified which included critical pathways with specified directionality. The associated steps gained and lost due to crosstalk during IPF were also identified. A serially connected system of five crucial genes was found, potentially controlled by nine miRNAs and eight transcription factors exclusively in IPF when compared to NSIP and Sarcoidosis. Findings from this study have been implemented into a comprehensive molecular and systems database on IPF to facilitate devising diagnostic and therapeutic solutions for this deadly disease.

De novo Sequencing and Transcriptome Analysis Reveal Key Genes Regulating Steroid Metabolism in Leaves, Roots, Adventitious Roots and Calli of Periploca sepium Bunge

Periploca sepium Bunge is a traditional medicinal plant, whose root bark is important for Chinese herbal medicine. Its major bioactive compounds are C21 steroids and periplocin, a kind of cardiac glycoside, which are derived from the steroid synthesis pathway. However, research on P. sepium genome or transcriptomes and their related genes has been lacking for a long time. In this study we estimated this species nuclear genome size at 170 Mb (using flow cytometry). Then, RNA sequencing of four different tissue samples of P. sepium (leaves, roots, adventitious roots, and calli) was done using the sequencing platform Illumina/Solexa Hiseq 2,500. After de novo assembly and quantitative assessment, 90,375 all-transcripts and 71,629 all-unigenes were finally generated. Annotation efforts that used a number of public databases resulted in detailed annotation information for the transcripts. In addition, differentially expressed genes (DEGs) were identified by using digital gene profiling based on the reads per kilobase of transcript per million reads mapped (RPKM) values. Compared with the leaf samples (L), up-regulated genes and down-regulated genes were eventually obtained. To deepen our understanding of these DEGs, we performed two enrichment analyses: gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG). Here, the analysis focused upon the expression characteristics of those genes involved in the terpene metabolic pathway and the steroid biosynthesis pathway, to better elucidate the molecular mechanism of bioactive steroid synthesis in P. sepium. The bioinformatics analysis enabled us to find many genes that are involved in bioactive steroid biosynthesis. These genes encoded acetyl-CoA acetyltransferase (ACAT), HMG-CoA synthase (HMGS), HMG-CoA reductase (HMGR), mevalonate kinase (MK), phosphomevalonate kinase (PMK), mevalonate diphosphate decarboxylase (MDD), isopentenylpyrophosphate isomerase (IPPI), farnesyl pyrophosphate synthase (FPS), squalene synthase (SS), squalene epoxidase (SE), cycloartenol synthase (CAS), sterol C-24 methyltransferase (SMT1), sterol-4alpha-methyl oxidase 1 (SMO1), sterol 14alpha-demethylase (CYP51/14-SDM), delta(14)-sterol reductase (FK/14SR), C-8,7 sterol isomerase (HYD1), sterol-4alpha-methyl oxidase 2 (SMO2), delta(7)-sterol-C5(6)-desaturase (STE1/SC5DL), 7-dehydrocholesterol reductase (DWF5/DHCR7), delta (24)-sterol reductase (DWF1/DHCR24), sterol 22-desaturase (CYP710A), progesterone 5beta-reductase (5β-POR), 3-beta-hydroxysteroid dehydrogenase (3β-HSD). This research will be helpful to further understand the mechanism of bioactive steroid biosynthesis in P. sepium, namely C21 steroid and periplocin biosynthesis.

Modular Design of Picroside-II Biosynthesis Deciphered through NGS Transcriptomes and Metabolic Intermediates Analysis in Naturally Variant Chemotypes of a Medicinal Herb, Picrorhiza kurroa

Picroside-II (P-II), an iridoid glycoside, is used as an active ingredient of various commercial herbal formulations available for the treatment of liver ailments. Despite this, the knowledge of P-II biosynthesis remains scarce owing to its negligence in Picrorhiza kurroa shoots which sets constant barrier for function validation experiments. In this study, we utilized natural variation for P-II content in stolon tissues of different P. kurroa accessions and deciphered its metabolic route by integrating metabolomics of intermediates with differential NGS transcriptomes. Upon navigating through high vs. low P-II content accessions (1.3-2.6%), we have established that P-II is biosynthesized via degradation of ferulic acid (FA) to produce vanillic acid (VA) which acts as its immediate biosynthetic precursor. Moreover, the FA treatment in vitro at 150 μM concentration provided further confirmation with 2-fold rise in VA content. Interestingly, the cross-talk between different compartments of P. kurroa, i.e., shoots and stolons, resolved spatial complexity of P-II biosynthesis and consequently speculated the burgeoning necessity to bridge gap between VA and P-II production in P. kurroa shoots. This work thus, offers a forward looking strategy to produce both P-I and P-II in shoot cultures, a step toward providing a sustainable production platform for these medicinal compounds via-à-vis relieving pressure from natural habitat of P. kurroa.

Spatial transcriptome analysis provides insights of key gene(s) involved in steroidal saponin biosynthesis in medicinally important herb Trillium govanianum

Trillium govanianum, an endangered medicinal herb native to the Himalaya, is less studied at the molecular level due to the non-availability of genomic resources. To facilitate the basic understanding of the key genes and regulatory mechanism of pharmaceutically important biosynthesis pathways, first spatial transcriptome sequencing of T. govanianum was performed. 151,622,376 (~11.5 Gb) high quality reads obtained using paired-end Illumina sequencing were de novo assembled into 69,174 transcripts. Functional annotation with multiple public databases identified array of genes involved in steroidal saponin biosynthesis and other secondary metabolite pathways including brassinosteroid, carotenoid, diterpenoid, flavonoid, phenylpropanoid, steroid and terpenoid backbone biosynthesis, and important TF families (bHLH, MYB related, NAC, FAR1, bZIP, B3 and WRKY). Differentially expressed large number of transcripts, together with CYPs and UGTs suggests involvement of these candidates in tissue specific expression. Combined transcriptome and expression analysis revealed that leaf and fruit tissues are the main site of steroidal saponin biosynthesis. In conclusion, comprehensive genomic dataset created in the current study will serve as a resource for identification of potential candidates for genetic manipulation of targeted bioactive metabolites and also contribute for development of functionally relevant molecular marker resource to expedite molecular breeding and conservation efforts in T. govanianum.

De novo sequencing and comparative analysis of leaf transcriptomes of diverse condensed tannin-containing lines of underutilized Psophocarpus tetragonolobus (L.) DC

Condensed tannin (CT) or proanthocyanidin (PA) is a unique group of phenolic metabolite with high molecular weight with specific structure. It is reported that, the presence of high-CT in the legumes adversely affect the nutrients in the plant and impairs the digestibility upon consumption by animals. Winged bean (Psophocarpus tetragonolobus (L.) DC.) is one of the promising underutilized legume with high protein and oil-content. One of the reasons for its underutilization is due to the presence of CT. Transcriptome sequencing of leaves of two diverse CT-containing lines of P. tetragonolobus was carried out on Illumina Nextseq 500 sequencer to identify the underlying genes and contigs responsible for CT-biosynthesis. RNA-Seq data generated 102586 and 88433 contigs for high (HCTW) and low CT (LCTW) lines of P. tetragonolobus, respectively. Based on the similarity searches against gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) database revealed 5210 contigs involved in 229 different pathways. A total of 1235 contigs were detected to differentially express between HCTW and LCTW lines. This study along with its findings will be helpful in providing information for functional and comparative genomic analysis of condensed tannin biosynthesis in this plant in specific and legumes in general.

Comparative Transcriptome Analysis of Chinary, Assamica and Cambod tea (Camellia sinensis) Types during Development and Seasonal Variation using RNA-seq Technology

Tea quality and yield is influenced by various factors including developmental tissue, seasonal variation and cultivar type. Here, the molecular basis of these factors was investigated in three tea cultivars namely, Him Sphurti (H), TV23 (T), and UPASI-9 (U) using RNA-seq. Seasonal variation in these cultivars was studied during active (A), mid-dormant (MD), dormant (D) and mid-active (MA) stages in two developmental tissues viz. young and old leaf. Development appears to affect gene expression more than the seasonal variation and cultivar types. Further, detailed transcript and metabolite profiling has identified genes such as F3'H, F3'5'H, FLS, DFR, LAR, ANR and ANS of catechin biosynthesis, while MXMT, SAMS, TCS and XDH of caffeine biosynthesis/catabolism as key regulators during development and seasonal variation among three different tea cultivars. In addition, expression analysis of genes related to phytohormones such as ABA, GA, ethylene and auxin has suggested their role in developmental tissues during seasonal variation in tea cultivars. Moreover, differential expression of genes involved in histone and DNA modification further suggests role of epigenetic mechanism in coordinating global gene expression during developmental and seasonal variation in tea. Our findings provide insights into global transcriptional reprogramming associated with development and seasonal variation in tea.

Transcriptomic resources and marker validation for diploid and polyploid Veronica (Plantaginaceae) from New Zealand and Europe

PREMISE OF THE STUDY

Polyploidy may generate novel variation, leading to adaptation and species diversification. An excellent natural system to study polyploid evolution in a comparative framework is Veronica (Plantaginaceae), which comprises several parallel, recently evolved polyploid series.

METHODS

Over 105 million Illumina paired-end sequence reads were generated from cDNA libraries of leaf tissue from eight individuals representing three European and four New Zealand species. Forty-eight simple sequence repeat (SSR) and 48 low-copy nuclear (LCN) markers were developed and validated with Fluidigm microfluidic PCR and Illumina MiSeq amplicon sequencing on 48 different individuals each.

RESULTS

Individual Trinity assemblies were similar regarding annotated transcripts (13,009-14,271), mean contig length (635-742 bp), N50 value (916-1133 bp), E90N50 value (1099-1308 bp), contigs with positive BLAST hits (42-63%), and gene ontology terms. Analyses of 29,738 single-nucleotide polymorphisms (8746 phylogenetically informative) mined from these transcriptomes plus two outgroups (Picrorhiza kurrooa and Plantago ovata) showed moderate to high bootstrap support for all branches and reticulation among sampled European Veronica.

DISCUSSION

The transcriptome sequences themselves, as well as the validated SSR (40/48) and LCN (11/48) markers derived from them, show inter- and intraspecific genetic variation. These resources will be invaluable for future population genetic, phylogenetic, and functional genetic investigations in polyploid Veronica.

Identifying wrong assemblies in de novo short read primary sequence assembly contigs

With the advent of short-reads-based genome sequencing approaches, large number of organisms are being sequenced all over the world. Most of these assemblies are done using some de novo short read assemblers and other related approaches. However, the contigs produced this way are prone to wrong assembly. So far, there is a conspicuous dearth of reliable tools to identify mis-assembled contigs. Mis-assemblies could result from incorrectly deleted or wrongly arranged genomic sequences. In the present work various factors related to sequence, sequencing and assembling have been assessed for their role in causing mis-assembly by using different genome sequencing data. Finally, some mis-assembly detecting tools have been evaluated for their ability to detect the wrongly assembled primary contigs, suggesting a lot of scope for improvement in this area. The present work also proposes a simple unsupervised learning-based novel approach to identify mis-assemblies in the contigs which was found performing reasonably well when compared to the already existing tools to report mis-assembled contigs. It was observed that the proposed methodology may work as a complementary system to the existing tools to enhance their accuracy.

Discerning picroside-I biosynthesis via molecular dissection of in vitro shoot regeneration in Picrorhiza kurroa

Expression analysis of primary and secondary metabolic pathways genes vis-à-vis shoot regeneration revealed developmental regulation of picroside-I biosynthesis in Picrorhiza kurroa. Picroside-I (P-I) is an important iridoid glycoside used in several herbal formulations for treatment of various disorders. P-I is synthesized in shoots of Picrorhiza kurroa and Picrorhiza scrophulariiflora. Current study reports on understanding P-I biosynthesis in different morphogenetic stages, viz. plant segment (PS), callus initiation (CI), callus mass (CM), shoot primordia (SP), multiple shoots (MS) and fully developed (FD) stages of P. kurroa. Expression analysis of genes involved in primary and secondary metabolism revealed that genes encoding HMGR, PMK, DXPS, ISPE, GS, G10H, DAHPS and PAL enzymes of MVA, MEP, iridoid and shikimate/phenylpropanoid pathways showed significant modulation of expression in SP, MS and FD stages in congruence with P-I content compared to CM stage. While HK, PK, ICDH, MDH and G6PDH showed high expression in MS and FD stages of P. kurroa, RBA, HisK and CytO showed high expression with progress in regeneration of shoots. Quantitative expression analysis of secondary metabolism genes at two temperatures revealed that 7 genes HMGR, PMK, DXPS, GS, G10H, DAHPS and PAL showed high transcript abundance (32-87-folds) in FD stage derived from leaf and root segments at 15 °C compared to 25 °C in P. kurroa. Further screening of these genes at species level showed high expression pattern in P. kurroa (6-19-folds) vis-à-vis P. scrophulariiflora that was in corroboration with P-I content. Therefore, current study revealed developmental regulation of P-I biosynthesis in P. kurroa which would be useful in designing a suitable genetic intervention study by targeting these genes for enhancing P-I production.

Transcriptome Analysis Reveals Candidate Genes involved in Blister Blight defense in Tea (Camellia sinensis (L) Kuntze)

To unravel the molecular mechanism of defense against blister blight (BB) disease caused by an obligate biotrophic fungus, Exobasidium vexans, transcriptome of BB interaction with resistance and susceptible tea genotypes was analysed through RNA-seq using Illumina GAIIx at four different stages during ~20-day disease cycle. Approximately 69 million high quality reads were assembled de novo, yielding 37,790 unique transcripts with more than 55% being functionally annotated. Differentially expressed, 149 defense related transcripts/genes, namely defense related enzymes, resistance genes, multidrug resistant transporters, transcription factors, retrotransposons, metacaspases and chaperons were observed in RG, suggesting their role in defending against BB. Being present in the major hub, putative master regulators among these candidates were identified from predetermined protein-protein interaction network of Arabidopsis thaliana. Further, confirmation of abundant expression of well-known RPM1, RPS2 and RPP13 in quantitative Real Time PCR indicates salicylic acid and jasmonic acid, possibly induce synthesis of antimicrobial compounds, required to overcome the virulence of E. vexans. Compendiously, the current study provides a comprehensive gene expression and insights into the molecular mechanism of tea defense against BB to serve as a resource for unravelling the possible regulatory mechanism of immunity against various biotic stresses in tea and other crops.

Exogenous feeding of immediate precursors reveals synergistic effect on picroside-I biosynthesis in shoot cultures of Picrorhiza kurroa Royle ex Benth

In the current study, we asked how the supply of immediate biosynthetic precursors i.e. cinnamic acid (CA) and catalpol (CAT) influences the synthesis of picroside-I (P-I) in shoot cultures of P. kurroa. Our results revealed that only CA and CA+CAT stimulated P-I production with 1.6-fold and 4.2-fold, respectively at 2.5 mg/100 mL concentration treatment. Interestingly, feeding CA+CAT not only directed flux towards p-Coumaric acid (p-CA) production but also appeared to trigger the metabolic flux through both shikimate/phenylpropanoid and iridoid pathways by utilizing more of CA and CAT for P-I biosynthesis. However, a deficiency in the supply of either the iridoid or the phenylpropanoid precursor limits flux through the respective pathways as reflected by feedback inhibition effect on PAL and decreased transcripts expressions of rate limiting enzymes (DAHPS, CM, PAL, GS and G10H). It also appears that addition of CA alone directed flux towards both p-CA and P-I production. Based on precursor feeding and metabolic fluxes, a current hypothesis is that precursors from both the iridoid and shikimate/phenylpropanoid pathways are a flux limitation for P-I production in shoot cultures of P. kurroa plants. This work thus sets a stage for future endeavour to elevate production of P-I in cultured plant cells.

Transcriptome sequencing and comparative analysis of Schizochytrium mangrovei PQ6 at different cultivation times

OBJECTIVE

The heterotrophic marine microalga, Schizochytrium mangrovei PQ6, synthesizes large amounts of polyunsaturated fatty acids (PUFAs) with possible nutritional applications. We characterized the transcriptome of S. mangrovei PQ6, focusing on lipid metabolism pathways throughout growth.

RESULT

Cell growth, total lipid, and docosahexaenoic acid (DHA, 22:6n-3) contents of S. mangrovei PQ6 in 500 ml batch cultures rapidly increased on day 1 in cultivation and reached their maximum levels on day 5. Maximum lipid accumulation in 500 ml batch cultures occurred on day 5, with total lipid and DHA contents reaching 33.2 ± 1.25% of dry cell weight (DCW) and 136 mg/g DCW, respectively. 11,025 unigenes, 28,617 unigenes and 18,480 unigenes from the transcriptomes of samples collected on day 1, 3, and 5 in cultivation were identified, respectively. These unigenes of the three samples were further assembled into 30,782 unigenes with an average size of 673 bp and N50 of 950 bp, and a total of 9,980 unigenes were annotated in public protein databases. 93 unigenes involved in lipid metabolism in which expression patterns corresponded with total lipid and DHA accumulation patterns were identified.

CONCLUSION

The possible roles of PUFAs pathways, such as those mediated by fatty acid synthase, polyketide synthase, and desaturase/elongase, co-exist in S. mangrovei PQ6.

Transcriptome Analysis of Differentially Expressed Genes Involved in Proanthocyanidin Accumulation in the Rhizomes of Fagopyrum dibotrys and an Irradiation-Induced Mutant

The rhizome of Fagopyrum dibotrys is a traditional Chinese medicine that has recently gained attention due to substantial findings regarding its bioactive proanthocyanidin (PA) compounds. However, the molecular mechanism underlying PA accumulation in F. dibotrys remains elusive. We previously obtained an irradiation-induced mutant (RM_R) of F. dibotrys that had a higher PA content compared to that of the wild-type (CK_R). The present study aimed to elucidate the molecular mechanism underlying PA accumulation in F. dibotrys by comparing the rhizome transcriptomes of the irradiation-induced mutant and wild-type using RNA-seq analysis. A total of 53,540 unigenes were obtained, of which 29,901 (55.84%) were annotated based on BLAST searches against public databases, and 501 unique sequences were differentially expressed between the two samples, which consisted of 204 up-regulated and 297 down-regulated unigenes. Further analysis showed that the expression patterns of some unigenes encoding enzymes involved in PAs biosynthesis in F. dibotrys rhizomes differed between RM_R and CK_R. In addition, we identified transcription factor families and several cytochrome P450s that may be involved in PA regulation in F. dibotrys. Finally, 12 unigenes that encode PA biosynthetic enzymes were confirmed by qRT-PCR analysis. This study sheds light on the molecular mechanism underlying radiation-mediated flavonoid accumulation and regulation in F. dibotrys rhizomes. These results will also provide a platform for further functional genomic research on this particular species.