Functional differentiation and spatial-temporal co-expression networks of the NBS-encoding gene family in Jilin ginseng, Panax ginseng C.A. Meyer

Beyond genome: Advanced omics progress of Panax ginseng

Ginseng is a perennial herb of the genus Panax in the family Araliaceae as one of the most important traditional medicine. Genomic studies of ginseng assist in the systematic discovery of genes related to bioactive ginsenosides biosynthesis and resistance to stress, which are of great significance in the conservation of genetic resources and variety improvement. The transcriptome reflects the difference and consistency of gene expression, and transcriptomics studies of ginseng assist in screening ginseng differentially expressed genes to further explore the powerful gene source of ginseng. Protein is the ultimate bearer of ginseng life activities, and proteomic studies of ginseng assist in exploring the biosynthesis and regulation of secondary metabolites like ginsenosides and the molecular mechanism of ginseng adversity adaptation at the overall level. In this review, we summarize the current status of ginseng research in genomics, transcriptomics and proteomics, respectively. We also discuss and look forward to the development of ginseng genome allele mapping, ginseng spatiotemporal, single-cell transcriptome, as well as ginseng post-translational modification proteome. We hope that this review will contribute to the in-depth study of ginseng and provide a reference for future analysis of ginseng from a systems biology perspective.

Integrative transcriptome analysis identifies new oxidosqualene cyclase genes involved in ginsenoside biosynthesis in Jilin ginseng

BACKGROUND

Jilin ginseng, Panax ginseng, is a valuable medicinal herb whose ginsenosides are its major bioactive components. The ginseng oxidosqualene cyclase (PgOSC) gene family is known to play important roles in ginsenoside biosynthesis, but few members of the gene family have been functionally studied.

METHODS

The PgOSC gene family has been studied by an integrated analysis of gene expression-ginsenoside content correlation, gene mutation-ginsenoside content association and gene co-expression network, followed by functional analysis through gene regulation.

RESULTS

We found that five of the genes in the PgOSC gene family, including two published ginsenoside biosynthesis genes and three new genes, were involved in ginsenoside biosynthesis. Not only were the expressions of these genes significantly correlated with ginsenoside contents, but also their nucleotide mutations significantly influenced ginsenoside contents. These results were further verified by regulation analysis of the genes by methyl jasmonate (MeJA) in ginseng hairy roots. Four of these five PgOSC genes were mapped to the ginsenoside biosynthesis pathway. These PgOSC genes expressed differently across tissues, but relatively consistent across developmental stages. These PgOSC genes formed a single co-expression network with those published ginsenoside biosynthesis genes, further confirming their roles in ginsenoside biosynthesis. When the network varied, ginsenoside biosynthesis was significantly influenced, thus revealing the molecular mechanism of ginsenoside biosynthesis.

CONCLUSION

At least five of the PgOSC genes, including the three newly identified and two published PgOSC genes, are involved in ginsenoside biosynthesis. These results provide gene resources and knowledge essential for enhanced research and applications of ginsenoside biosynthesis in ginseng.

Basic leucine zipper (bZIP) transcription factor genes and their responses to drought stress in ginseng, Panax ginseng C.A. Meyer

BACKGROUND

Ginseng is an important medicinal herb in Asia and Northern America. The basic leucine zipper (bZIP) transcription factor genes play important roles in many biological processes and plant responses to abiotic and biotic stresses, such as drought stress. Nevertheless, the genes remain unknown in ginseng.

RESULTS

Here, we report 91 bZIP genes identified from ginseng, designated PgbZIP genes. These PgbZIP genes were alternatively spliced into 273 transcripts. Phylogenetic analysis grouped the PgbZIP genes into ten groups, including A, B, C, D, E, F, G, H, I and S. Gene Ontology (GO) categorized the PgbZIP genes into five functional subcategories, suggesting that they have diversified in functionality, even though their putative proteins share a number of conserved motifs. These 273 PgbZIP transcripts expressed differentially across 14 tissues, the roots of different ages and the roots of different genotypes. However, the transcripts of the genes expressed coordinately and were more likely to form a co-expression network. Furthermore, we studied the responses of the PgbZIP genes to drought stress in ginseng using a random selection of five PgbZIP genes, including PgbZIP25, PgbZIP38, PgbZIP39, PgbZIP53 and PgbZIP54. The results showed that all five PgbZIP genes responded to drought stress in ginseng, indicating that the PgbZIP genes play important roles in ginseng responses to drought stress.

CONCLUSIONS

These results provide knowledge and gene resources for deeper functional analysis of the PgbZIP genes and molecular tools for enhanced drought tolerance breeding in ginseng.

Analysis of the genes controlling three quantitative traits in three diverse plant species reveals the molecular basis of quantitative traits

Most traits of agricultural importance are quantitative traits controlled by numerous genes. However, it remains unclear about the molecular mechanisms underpinning quantitative traits. Here, we report the molecular characteristics of the genes controlling three quantitative traits randomly selected from three diverse plant species, including ginsenoside biosynthesis in ginseng (Panax ginseng C.A. Meyer), fiber length in cotton (Gossypium hirsutum L. and G. barbadense L.) and grain yield in maize (Zea mays L.). We found that a vast majority of the genes controlling a quantitative trait were significantly more likely spliced into multiple transcripts while they expressed. Nevertheless, only one to four, but not all, of the transcripts spliced from each of the genes were significantly correlated with the phenotype of the trait. The genes controlling a quantitative trait were multiple times more likely to form a co-expression network than other genes expressed in an organ. The network varied substantially among genotypes of a species and was associated with their phenotypes. These findings indicate that the genes controlling a quantitative trait are more likely pleiotropic and functionally correlated, thus providing new insights into the molecular basis underpinning quantitative traits and knowledge necessary to develop technologies for efficient manipulation of quantitative traits.

Identification, characterization and functional differentiation of the NAC gene family and its roles in response to cold stress in ginseng, Panax ginseng C.A. Meyer

The NAC gene family is one of the important plant-specific transcription factor families involved in variety of physiological processes. It has been found in several plant species; however, little is known about the gene family in ginseng, Panax ginseng C.A. Meyer. Here we report identification and systematic analysis of this gene family in ginseng. A total of 89 NAC genes, designated PgNAC01 to PgNAC89, are identified. These genes are alternatively spliced into 251 transcripts at fruiting stage of a four-year-old ginseng plant. The genes of this gene family have five conserved motifs and are clustered into 11 subfamilies, all of which are shared with the genes of the NAC gene families identified in the dicot and monocot model plant species, Arabidopsis and rice. This result indicates that the PgNAC gene family is an ancient and evolutionarily inactive gene family. Gene ontology (GO) analysis shows that the functions of the PgNAC gene family have been substantially differentiated; nevertheless, over 86% the PgNAC transcripts remain functionally correlated. Finally, five of the PgNAC genes, PgNAC05-2, PgNAC41-2, PgNAC48, PgNAC56-1, and PgNAC59, are identified to be involved in plant response to cold stress, suggesting that this gene family plays roles in response to cold stress in ginseng. These results, therefore, provide new insights into functional differentiation and evolution of a gene family in plants and gene resources necessary to comprehensively determine the functions of the PgNAC gene family in response to cold and other abiotic stresses in ginseng.

The bHLH gene family and its response to saline stress in Jilin ginseng, Panax ginseng C.A. Meyer

Basic helix-loop-helix (bHLH) gene family is a gene family of transcription factors that plays essential roles in plant growth and development, secondary metabolism and response to biotic and abiotic stresses. Therefore, a comprehensive knowledge of the bHLH gene family is paramount to understand the molecular mechanisms underlying these processes and develop advanced technologies to manipulate the processes efficiently. Ginseng, Panax ginseng C.A. Meyer, is a well-known medicinal herb; however, little is known  about the bHLH genes (PgbHLH) in the species. Here, we identified 137 PgbHLH genes from Jilin ginseng cultivar, Damaya, widely cultivated in Jilin, China, of which 50 are newly identified by pan-genome analysis. These 137 PgbHLH genes were phylogenetically classified into 26 subfamilies, suggesting their sequence diversification. They are alternatively spliced into 366 transcripts in a 4-year-old plant and involved in 11 functional subcategories of the gene ontology, indicating their functional differentiation in ginseng. The expressions of the PgbHLH genes dramatically vary spatio-temporally and across 42 genotypes, but they are still somehow functionally correlated. Moreover, the PgbHLH gene family, at least some of its genes, is shown to have roles in plant response to the abiotic stress of saline. These results provide a new insight into the evolution and functional differentiation of the bHLH gene family in plants, new bHLH genes to the PgbHLH gene family, and saline stress-responsive genes for genetic improvement in ginseng and other plant species.

Structural variation, functional differentiation and expression characteristics of the AP2/ERF gene family and its response to cold stress and methyl jasmonate in Panax ginseng C.A. Meyer

The APETALA2/Ethylene Responsive Factor (AP2/ERF) gene family has been shown to play a crucial role in plant growth and development, stress responses and secondary metabolite biosynthesis. Nevertheless, little is known about the gene family in ginseng (Panax ginseng C.A. Meyer), an important medicinal herb in Asia and North America. Here, we report the systematic analysis of the gene family in ginseng using several transcriptomic databases. A total of 189 putative AP2/ERF genes, defined as PgERF001 through PgERF189, were identified and these PgERF genes were spliced into 397 transcripts. The 93 PgERF genes that have complete AP2 domains in open reading frame were classified into five subfamilies, DREB, ERF, AP2, RAV and Soloist. The DREB subfamily and ERF subfamily were further clustered into four and six groups, respectively, compared to the 12 groups of these subfamilies found in Arabidopsis thaliana. Gene ontology categorized these 397 transcripts of the 189 PgERF genes into eight functional subcategories, suggesting their functional differentiation, and they have been especially enriched for the subcategory of nucleic acid binding transcription factor activity. The expression activity and networks of the 397 PgERF transcripts have substantially diversified across tissues, developmental stages and genotypes. The expressions of the PgERF genes also significantly varied, when ginseng was subjected to cold stress, as tested using six PgERF genes, PgERF073, PgERF079, PgERF110, PgERF115, PgERF120 and PgERF128, randomly selected from the DREB subfamily. This result suggests that the DREB subfamily genes play an important role in plant response to cold stress. Finally, we studied the responses of the PgERF genes to methyl jasmonate (MeJA). We found that 288 (72.5%) of the 397 PgERF gene transcripts responded to the MeJA treatment, with 136 up-regulated and 152 down-regulated, indicating that most members of the PgERF gene family are responsive to MeJA. These results, therefore, provide new resources and knowledge necessary for family-wide functional analysis of the PgERF genes in ginseng and related species.

Till 2018: a survey of biomolecular sequences in genus Panax

Ginseng is popularly known to be the king of ancient medicines and is used widely in most of the traditional medicinal compositions due to its various pharmaceutical properties. Numerous studies are being focused on this plant's curative effects to discover their potential health benefits in most human diseases, including cancer- the most life-threatening disease worldwide. Modern pharmacological research has focused mainly on ginsenosides, the major bioactive compounds of ginseng, because of their multiple therapeutic applications. Various issues on ginseng plant development, physiological processes, and agricultural issues have also been studied widely through state-of-the-art, high-throughput sequencing technologies. Since the beginning of the 21st century, the number of publications on ginseng has rapidly increased, with a recent count of more than 6,000 articles and reviews focusing notably on ginseng. Owing to the implementation of various technologies and continuous efforts, the ginseng plant genomes have been decoded effectively in recent years. Therefore, this review focuses mainly on the cellular biomolecular sequences in ginseng plants from the perspective of the central molecular dogma, with an emphasis on genomes, transcriptomes, and proteomes, together with a few other related studies.

Transcriptome-Wide Identification, Evolutionary Analysis, and GA Stress Response of the GRAS Gene Family in Panax ginseng C. A. Meyer

GRAS transcription factors are a kind of plant-specific transcription factor that have been found in a variety of plants. According to previous studies, GRAS proteins are widely involved in the physiological processes of plant signal transduction, stress, growth and development. The Jilin ginseng (Panax ginseng C.A. Meyer) is a heterogeneous tetraploid perennial herb of the Araliaceae family, ginseng genus. Important information regarding the GRAS transcription factors has not been reported in ginseng. In this study, 59 Panax ginseng GRAS (PgGRAS) genes were obtained from the Jilin ginseng transcriptome data and divided into 13 sub-families according to the classification of Arabidopsis thaliana. Through systematic evolution, structural variation, function and gene expression analysis, we further reveal GRAS’s potential function in plant growth processes and its stress response. The expression of PgGRAS genes responding to gibberellin acids (GAs) suggests that these genes could be activated after application concentration of GA. The qPCR analysis result shows that four PgGRAS genes belonging to the DELLA sub-family potentially have important roles in the GA stress response of ginseng hairy roots. This study provides not only a preliminary exploration of the potential functions of the GRAS genes in ginseng, but also valuable data for further exploration of the candidate PgGRAS genes of GA signaling in Jilin ginseng, especially their roles in ginseng hairy root development and GA stress response.

Transcriptome analysis identifies strong candidate genes for ginsenoside biosynthesis and reveals its underlying molecular mechanism in Panax ginseng C.A. Meyer

Ginseng, Panax ginseng C.A. Meyer, is one of the most important medicinal herbs for human health and medicine in which ginsenosides are known to play critical roles. The genes from the cytochrome P450 (CYP) gene superfamily have been shown to play important roles in ginsenoside biosynthesis. Here we report genome-wide identification of the candidate PgCYP genes for ginsenoside biosynthesis, development of functional SNP markers for its manipulation and systems analysis of its underlying molecular mechanism. Correlation analysis identified 100 PgCYP genes, including all three published ginsenoside biosynthesis PgCYP genes, whose expressions were significantly correlated with the ginsenoside contents. Mutation association analysis identified that six of these 100 PgCYP genes contained SNPs/InDels that were significantly associated with ginsenosides biosynthesis (P ≤ 1.0e-04). These six PgCYP genes, along with all ten published ginsenoside biosynthesis genes from the PgCYP and other gene families, formed a strong co-expression network, even though they varied greatly in spatio-temporal expressions. Therefore, this study has identified six new ginsenoside biosynthesis candidate genes, provided a genome-wide insight into how they are involved in ginsenoside biosynthesis and developed a set of functional SNP markers useful for enhanced ginsenoside biosynthesis research and breeding in ginseng and related species.

Structural Variation, Functional Differentiation, and Activity Correlation of the Cytochrome P450 Gene Superfamily Revealed in Ginseng

Ginseng ( C.A. Mey.) is one of the most important medicinal herbs for human health and medicine, for which ginsenosides are the major bioactive components. The cytochrome P450 genes, , form a large gene superfamily; however, only three genes have been identified from ginseng and shown to be involved in ginsenoside biosynthesis, indicating the importance of the gene superfamily in the process. Here we report genome-wide identification and systems analysis of the genes in ginseng, defined as genes. We identified 414 genes, including the three published genes. These genes formed a superfamily consisting of 41 gene families, with a substantial diversity in phylogeny and dramatic variation in spatiotemporal expression. Gene ontology (GO) analysis categorized the gene superfamily into 12 functional subcategories distributing among all three primary functional categories, suggesting its functional differentiation. Nevertheless, the majority of its gene members expressed correlatively and tended to form a coexpression network and some of them were commonly regulated in expression across tissues and developmental stages. These results have led to genome-wide identification of genes useful for genome-wide identification of the genes involved in ginsenoside biosynthesis in ginseng and provided the first insight into how a gene superfamily functionally differentiates and acts correlatively in plants.

Evolution, functional differentiation, and co-expression of the RLK gene family revealed in Jilin ginseng, Panax ginseng C.A. Meyer

Most genes in a genome exist in the form of a gene family; therefore, it is necessary to have knowledge of how a gene family functions to comprehensively understand organismal biology. The receptor-like kinase (RLK)-encoding gene family is one of the most important gene families in plants. It plays important roles in biotic and abiotic stress tolerances, and growth and development. However, little is known about the functional differentiation and relationships among the gene members within a gene family in plants. This study has isolated 563 RLK genes (designated as PgRLK genes) expressed in Jilin ginseng (Panax ginseng C.A. Meyer), investigated their evolution, and deciphered their functional diversification and relationships. The PgRLK gene family is highly diverged and formed into eight types. The LRR type is the earliest and most prevalent, while only the Lec type originated after P. ginseng evolved. Furthermore, although the members of the PgRLK gene family all encode receptor-like protein kinases and share conservative domains, they are functionally very diverse, participating in numerous biological processes. The expressions of different members of the PgRLK gene family are extremely variable within a tissue, at a developmental stage and in the same cultivar, but most of the genes tend to express correlatively, forming a co-expression network. These results not only provide a deeper and comprehensive understanding of the evolution, functional differentiation and correlation of a gene family in plants, but also an RLK genic resource useful for enhanced ginseng genetic improvement.