Panax notoginseng transcription factor WRKY15 modulates resistance to Fusarium solani by up-regulating osmotin-like protein expression and inducing JA/SA signaling pathways.

BACKGROUND: Panax notoginseng (Burk) F. H. Chen is a valuable traditional Chinese medicinal plant, but its commercial production is seriously affected by root rot caused by some pathogenic fungi, including Fusarium solani. Nevertheless, the genetic breeding for disease resistance of P. notoginseng remains limited. The WRKY transcription factors have been revealed to play important roles in plant defense responses, which might provide an inspiration for resistance improvement in P. notoginseng. RESULTS: In this study, the regulatory mechanism of transcription factor PnWRKY15 on P. notoginseng resistance to F. solani infection was revealed. The suppressed expression of PnWRKY15 via RNA interference increased the sensitivity of P. notoginseng to F. solani and decreased the expression levels of some defense-related genes, including PnOLP1, which encodes an osmotin-like protein that confers resistance to F. solani. Ectopic expression of PnWRKY15 in the model plant tobacco significantly enhanced the resistance to F. solani. Moreover, the transcriptome sequencing analysis discovered that some pathogenesis-related genes were expressed at higher levels in the PnWRKY15-overexpressing tobacco than that in the wild-type tobacco. In addition, the jasmonic acid (JA) and salicylic acid (SA) signaling pathways were evidently induced by PnWRKY15-overexpression, that was evidenced by that the JA and SA contents were significantly higher in the PnWRKY15-overexpressing tobacco than that in the wild-type. Furthermore, PnWRKY15, which was localized in the nucleus, can trans-activate and up-regulate PnOLP1 expression according to the EMSA, yeast one-hybrid and co-expression assays. CONCLUSIONS: PnWRKY15 contributes to P. notoginseng resistance to F. solani by up-regulating the expression of resistance-related gene PnOLP1 and activating JA/SA signaling pathways. These findings will help to further elucidate the transcriptional regulatory mechanism associated with the P. notoginseng defense response to F. solani.

First report of a Panax notoginseng leaf disease caused by Alternaria alternata in China.

Panax notoginseng (Burk.) F. H. Chen is a perennial plant species in the family Araliaceae, and its roots and rhizome are precious materials for the production of traditional Chinese medicine. From April to June, 2018, new disease symptoms were detected on the mature leaves of 2- and 3-year-old Panax notoginseng (P. notoginseng) in Wenshan Autonomous Prefecture, Yunnan Province, China, and the disease incidence was about 10%-15% among the analyzed fields (3.6 ha, 23°49'46.99″ N, 104°06'12.99″ E, 1,631 m elevation). The diseased leaves had dark brown necrotic lesions (0.9-2.5 × 1.0-3.5 cm) and curled downward. As the disease progressed, the necrosis gradually spread along the vein to other leaf parts, eventually covering the whole leaf. In the late disease stage, the whole leaf was decayed and yellowed. For pathogen isolation, infected leaves (n=20) were surface sterilized in 1% sodium hypochlorite and washed with sterilized distilled water for 3 mins before being cut into smaller pieces (~1cm2), then placed onto potato dextrose agar (PDA) medium and incubated at 28°C under aseptic conditions for 3 days. The hypha around leaf discs were transferred onto the new PDA. A total of 20 colonies (SQ1~20) were obtained and purified by single spore culture for morphological characterization and molecular biological identification. The colonies of all isolates were nearly round, grayish white at the initial stage, and then turned to grayish brown. In addition, microscopic examination (100× magnification) of 20 isolates revealed dark, septate, and sparsely branched conidiophores as well as dark brown conidia with short conical beaks at their tip. Additionally, conidia (solitary or in short chains) were typically oval or club-shaped and had 0-2 longitudinal septa and 2-4 transverse septa (20-35 × 8-12 µm) (n = 50). Moreover, the conidia had a smooth or verrucose surface. Their morphological characteristics were similar to those descriptions given for members of section Alternaria by Lawrence et al. (2016). In order to further identify pathogenic species, genomic DNA was extracted from the colonies (SQ1~20) using a modified cetyltrimethylammonium bromide (CTAB) method (Loganathan et al. 2014). The sequences of internal transcribed spacer regions of ribosomal DNA (rDNA ITS) and partial RNA polymerase II second subunit gene (RPB2) were amplified by PCR using fungal universal primers ITS1/ITS4 (White et al. 1990) and fRPB2-5F/fRPB2-7cR (Liu et al. 1999), respectively. The DNA sequencing shows that ITS sequences from 20 isolates were totally same, and so did the RPB2 sequences (supplementary material). BLASTN analysis of NCBI database indicated that the RPB2 and ITS sequences have the highest nucleotide homology to A. Alternata ITS (MW008974) and RPB2 (LC132700), respectively. These two gene sequences were submitted to GenBank [Accession numbers ON075466 (ITS) and OP572232 (RPB2)]. Phylogenetic trees based on the combined ITS and RPB2 sequences were constructed by maximum parsimony method. The referenced ITS and RPB2 sequences of Alternaria were from three published articles (Rama et al. 2020; Sun et al. 2021; Wee et al. 2006). Phylogenetic analysis revealed that this isolate was clustered with A. alternata. Therefore, the morphology-based preliminary identification was verified by the phylogenetic analysis, and the isolate from diseased P. notoginseng leaves was A. alternata. To confirm its pathogenicity, the fungal isolate was assessed with 40 1-year-old healthy P. notoginseng plants in a greenhouse. Among them, the leaves of 20 of P. notoginseng plants were wounded using a sterile needle (seven or eight wounds per leaf) and then inoculated with 1mL conidial suspension (1 × 106 conidia/mL) prepared from 7-day-old fungal cultures grown on PDA medium. The inoculated plants were covered with plastic bags at 25°C for 24 h to maintain humidity, and then transferred to the greenhouse maintained at 28°C with a 16-h day/8-h night cycle and continuous misting. The other 20 control plants were only wounded and sprayed with sterile water. Typical necrotic lesions were detected on all of the inoculated P. notoginseng leaves cultivated in the greenhouse for 1 week post-inoculation. As the disease continued to develop, the necrotic lesions enlarged, and the infected leaves turned yellow and withered. These symptoms were similar to those observed on the naturally infected P. notoginseng. In contrast, the mock-inoculated control plants remained healthy. Furthermore, the fungus re-isolated from the infected P. notoginseng leaves in the pot experiment had similar morphological characteristics as the original strain. In addition, its genomic DNA was extracted for PCR analysis of ITS and RPB2 sequences, and the following DNA sequencing shows that the two DNA sequences were same as those of isolates SQ1~20, which confirmed that the re-isolated fungus was A. alternata. To the best of our knowledge, this is the first report of A. alternata causing a P. notoginseng leaf disease in China.

An MYB Transcription Factor Modulates Panax notoginseng Resistance Against the Root Rot Pathogen Fusarium solani by Regulating the Jasmonate Acid Signaling Pathway and Photosynthesis.

Root rot of Panax notoginseng, a precious Chinese medicinal plant, seriously impacts its sustainable production. However, the molecular regulatory mechanisms employed by P. notoginseng against root rot pathogens, including Fusarium solani, are still unclear. In this study, the PnMYB2 gene was isolated, and its expression was affected by independent treatments with four signaling molecules (methyl jasmonate, ethephon, salicylic acid, and hydrogen peroxide) as assessed by quantitative real-time PCR. Moreover, the PnMYB2 expression level was induced by F. solani infection. The PnMYB2 protein localized to the nucleus and may function as a transcription factor. When overexpressed in transgenic tobacco, the PnMYB2 gene conferred resistance to F. solani. Jasmonic acid (JA) metabolism and disease resistance-related genes were induced in the transgenic tobacco, and the JA content significantly increased compared with in the wild type. Additionally, transcriptome sequencing, Kyoto Encyclopedia of Genes and Genomes annotation enrichment, and metabolic pathway analyses of the differentially expressed genes in the transgenic tobacco revealed that JA metabolic, photosynthetic, and defense response-related pathways were activated. In summary, PnMYB2 is an important transcription factor in the defense responses of P. notoginseng against root rot pathogens that acts by regulating JA signaling, photosynthesis, and disease-resistance genes.

[Synergistic effect on biosynthesis of Panax notoginseng saponins by overexpressing a transcription factor PnbHLH and RNA interference of cycloartenol synthase gene].

This study cloned the transcription factor gene PnbHLH which held an open reading frame of 966 bp encoding 321 amino acids. This study constructed the overexpression vector of transcription factor PnbHLH of Panax notoginseng. The combination of PnbHLH overexpression and RNAi of the key enzyme gene PnCAS involved in the phytosterol biosynthesis was achieved in P. notoginseng cells, thus exploring the biosynthetic regulation of P. notoginseng saponins(PNS) by the synergistic effect of PnbHLH overexpression and PnCAS RNAi. The results showed that the PnbHLH transcription factor interacted with the promoters of key enzyme genes PnDS, PnSS and PnSE in the biosynthetic pathway of PNS, and then regulated the expression levels of key enzyme genes and affected the biosynthesis of saponins indirectly. Further study indicated that the synergistic effect of PnbHLH overexpression and PnCAS RNAi was a more effective approach to regulate the biosynthesis of saponins. Compared with the wild type and PnCAS RNAi cells of P. notoginseng, the contents of total saponins and monomeric saponins(Rd, Rb_1, Re, Rg_1 and R_1) were increased to some extent in the cell lines of PnbHLH overexpression and PnCAS RNAi. This indicated that the two ways of forward regulation and reverse regulation of saponin biosynthesis showed superposition effect. This study explored a more rational and efficient regulation strategy of PNS biosynthesis based on the advantages of multi-point regulation of transcription factors as well as the down-regulation of by-product synthesis of saponins.

Structure and Function of Rhizosphere Soil and Root Endophytic Microbial Communities Associated With Root Rot of Panax notoginseng.

Panax notoginseng (Burk.) F. H. Chen is a Chinese medicinal plant of the Araliaceae family used for the treatment of cardiovascular and cerebrovascular diseases in Asia. P. notoginseng is vulnerable to root rot disease, which reduces the yield of P. notoginseng. In this study, we analyzed the rhizosphere soil and root endophyte microbial communities of P. notoginseng from different geographical locations using high-throughput sequencing. Our results revealed that the P. notoginseng rhizosphere soil microbial community was more diverse than the root endophyte community. Rhodopseudomonas, Actinoplanes, Burkholderia, and Variovorax paradoxus can help P. notoginseng resist the invasion of root rot disease. Ilyonectria mors-panacis, Pseudomonas fluorescens, and Pseudopyrenochaeta lycopersici are pathogenic bacteria of P. notoginseng. The upregulation of amino acid transport and metabolism in the soil would help to resist pathogens and improve the resistance of P. notoginseng. The ABC transporter and gene modulating resistance genes can improve the disease resistance of P. notoginseng, and the increase in the number of GTs (glycosyltransferases) and GHs (glycoside hydrolases) families may be a molecular manifestation of P. notoginseng root rot. In addition, the complete genomes of two Flavobacteriaceae species and one Bacteroides species were obtained. This study demonstrated the microbial and functional diversity in the rhizosphere and root microbial community of P. notoginseng and provided useful information for a better understanding of the microbial community in P. notoginseng root rot. Our results provide insights into the molecular mechanism underlying P. notoginseng root rot and other plant rhizosphere microbial communities.

A Pathogenesis-Related Protein-Like Gene Is Involved in the Panax notoginseng Defense Response to the Root Rot Pathogen.

Pathogenesis-related proteins (PRs) are a class of proteins that accumulate in response to biotic and abiotic stresses to protect plants from damage. In this study, a gene encoding a PR-like protein (PnPR-like) was isolated from Panax notoginseng, which is used in traditional Chinese herbal medicines. An analysis of gene expression in P. notoginseng indicated that PnPR-like was responsive to an infection by the root rot pathogen Fusarium solani. The expression of this gene was induced by several signaling molecules, including methyl jasmonate, ethephon, hydrogen peroxide, and salicylic acid. The PnPR-like-GFP fusion gene was transiently expressed in onion (Allium cepa) epidermal cells, which revealed that PnPR-like is a cytoplasmic protein. The purified recombinant PnPR-like protein expressed in Escherichia coli had antifungal effects on F. solani and Colletotrichum gloeosporioides as well as inhibited the spore germination of F. solani. Additionally, the in vitro ribonuclease (RNase) activity of the recombinant PnPR-like protein was revealed. The PnPR-like gene was inserted into tobacco (Nicotiana tabacum) to verify its function. The gene was stably expressed in T2 transgenic tobacco plants, which exhibited more RNase activity and greater disease resistance than the wild-type tobacco. Moreover, the transient expression of hairpin RNA targeting PnPR-like in P. notoginseng leaves increased the susceptibility to F. solani and decreased the PnPR-like expression level. In conclusion, the cytoplasmic protein PnPR-like, which has RNase activity, is involved in the P. notoginseng defense response to F. solani.

A transcriptome analysis uncovers Panax notoginseng resistance to Fusarium solani induced by methyl jasmonate.

BACKGROUND: Panax notoginseng is a famous Chinese herbal medicine, but the root rot disease mainly caused by Fusarium solani severely reduces the yield and quality of its medicinal materials. OBJECTIVE: The defense priming in P. notoginseng through exogenous application of signaling molecule will supply theoretical support for the exogenous regulation of disease resistance in P. notoginseng. METHODS: In this study, the exogenous application of methyl jasmonate (MeJA) increased P. notoginseng's resistance to F. solani. Furthermore, the P. notoginseng transcriptome during F. solani infection was investigated through next-generation sequencing to uncover the resistance mechanism of P. notogingseng induced by MeJA. RESULTS: The de novo assembly of transcriptome sequences produced 80,551 unigenes, and 36,771 of these unigenes were annotated by at least one database. A differentially expressed gene analysis revealed that a large number of genes related to terpenoid backbone biosynthesis, phenylalanine metabolism, and plant-pathogen interactions were predominantly up-regulated by MeJA. Moreover, jasmonic acid (JA) biosynthesis-related genes and the JA signaling pathway genes, such as linoleate 13S-lipoxygenase, allene oxide cyclase, allene oxide synthase, TIFY, defensin, and pathogenesis-related proteins, showed increased transcriptional levels after inoculation with F. solani. Notably, according to the gene expression analysis, JA and ethylene signaling pathways may act synergistically to positively regulate the defense responses of P. notoginseng to F. solani. CONCLUSION: JA signaling appears to play a vital role in P. notoginseng responses to F. solani infection, which will be helpful in improving the disease resistance of P. notoginseng cultivars as well as in developing an environmentally friendly biological control method for root rot disease.

Oleanane-Type Saponins Biosynthesis in Panax notoginseng via Transformation of ß-Amyrin Synthase Gene from Panax japonicus.

Oleanane-type saponins considered as the main medicinal ingredients in Panax japonicus are not found in Panax notoginseng. ß-Amyrin synthase (ßAS) was recognized as the first key enzyme in the biosynthetic branch of oleanane-type saponins. In this study, ßAS gene from P. japonicus ( PjßAS) was transferred into P. notoginseng cells. Along with PjßAS expression in the transgenic cells, the expression levels of several key enzyme genes related to triterpenoid saponins biosynthesis and the content of P. notoginseng saponins were also increased. Two oleanane-type saponins, chikusetsusaponin IV and chikusetsusaponin IVa, contained in P. japonicus were first discovered in transgenic P. notoginseng cells. This study successfully constructed a biosynthetic pathway of oleanane-type saponins in P. notoginseng by introducing just one gene into the species. On the basis of this discovery and previous studies, the common biosynthetic pathway of triterpenoid saponins in Panax genus may be unified to some extent.

[Functional analysis of a chitinase gene PnCHI1 from Panax notoginseng].

Chitinases, a glycosidase enzyme that hydrolyzes chitin to N-acetylglucosamine, are widely found in plant cells, and they are an important part of plant antifungal defense system. The function of a Panax notoginseng chitinase gene PnCHI1 was characterized in this paper. Expression vector of PnCHI1 was constructed and transiently expressed in onion epidermal cells, and laser scanning confocal microscopy demonstrated that PnCHI1 was localized in the cell wall. Prokaryotic expression vector of PnCHI1 was also constructed, and recombinant protein of PnCHI1 was induced and purified. In vitro antibacterial assay showed that recombinant PnCHI1 protein had strong inhibitory activity on the mycelium growth of Fusarium solani, F. oxysporum and F. verticillioide. The function of PnCHI1 was further verified by reverse genetics. PnCHI1 expression vector was transferred into tobacco by Agrobacterium tumefaciens and expression of PnCHI1 was confirmed by qRT-PCR. It was found by leaf inoculation experiment that resistance of transgenic tobacco to F. solani was significantly increased. It is conclnded that: PnCHI1 is a chitinase localized in the cell wall, which inhibits several fungi which cause the root rot disease of P. notoginseng. Overexpression of this chitinase gene in tobacco greatly increased resistance to F. solani. PnCHI1 may be an important resistance gene in P. notoginseng that participates in the defense against root rot disease.

Small RNA profiles from Panax notoginseng roots differing in sizes reveal correlation between miR156 abundances and root biomass levels.

Plant genomes encode several classes of small regulatory RNAs (sRNAs) that play critical roles in both development and stress responses. Panax notoginseng (Burk.) F.H. Chen (P. notoginseng) is an important traditional Chinese herbal medicinal plant species for its haemostatic effects. Therefore, the root yield of P. notoginseng is a major economically important trait since the roots of P. notoginseng are the parts used to produce medicine. To identify sRNAs that are critical for the root biomass of P. notoginseng, we performed a comprehensive study of miRNA transcriptomes from P. notoginseng roots of different biomasses. We identified 675 conserved miRNAs, of which 180 pre-miRNAs are also identified, and three TAS3 loci in P. notoginseng. By using degradome sequencing, we identified 79 conserved miRNA:target or tasiRNA:target interactions, of which eight were further confirmed with the RLM 5'-RACE experiments. More importantly, our results revealed that a member of miR156 family and one of its SPL target genes have inverse expression levels, which is tightly correlated with greater root biomass contents. These results not only contributes to overall understanding of post-transcriptional gene regulation in roots of P. notoginseng but also could serve as markers for breeding P. notoginseng with greater root yield.

Molecular Cloning and Characterization of PnbHLH1 Transcription Factor in Panax notoginseng.

Panax notoginseng has been extensively used as a traditional Chinese medicine. In the current study, molecular cloning and characterization of PnbHLH1 transcription factor were explored in Panax notoginseng. The full length of the PnbHLH1 gene obtained by splicing was 1430 bp, encoding 321 amino acids. Prokaryotic expression vector pET-28a-PnbHLH1 was constructed and transferred into the BL21 prokaryotic expression strain. An electrophoretic mobility shift assay of PnbHLH1 protein binding to E-box cis-acting elements verified that PnbHLH1 belonged to the bHLH class transcription factor which could interact with the promoter region of the E-box core sequence. The expression levels of key genes involved in the biosynthesis of triterpenoid saponins in PnbHLH1 transgenic cells were higher than those in the wild cells. Similarly, the total saponin contents were increased in the PnbHLH1 transgenic cell lines compared with the wild cell lines. Such results suggest that the PnbHLH1 transcription factor is a positive regulator in the biosynthesis of triterpenoid saponins in Panax notoginseng.

[Cloning and expression analysis of a chitinase gene PnCHI1 from Panax notoginseng].

Chitinases(EC3.2.1.14), which are present in various organisms, catalyze the hydrolytic cleavage of chitin and play a vital role in plant defense mechanisms against fungal pathogens.In addition, the chitinases are well known to regulate plant growth and development and are involved in programmed cell death(PCD).A chitinase expressed sequence tag(EST) was isolated from Panax notoginseng, and the full-length cDNA of this EST was cloned with the method of rapid amplification of cDNA ends and named as PnCHI1. PnCHI1 was 1 022 bp in length and contained an intact open reading frame(ORF) of 822 bp, a 26 bp 5'-untranslated region(UTR), and a 174 bp 3'-UTR.The predicted protein of PnCHI1 with 273 amino acid residues belongs to glycoside hydrolase family 19 and fell into the class IV of chitinases through phylogenetic analysis.QRT-PCR analysis showed that the expression of PnCHI1 was induced by methyl jasmonate, ethylene, H2O2, and salicylic acid.PnCHI1 was quickly induced after inoculation with Alternaria panax.Moreover, the expression level of PnCHI1 was increased after pretreatment with methyl jasmonate, and then the transcription level of PnCHI1was sharp increased after inoculation with Fusarium solani,and the highest transcription level was achieved at 4 h post inoculation.But the expression level of PnCHI1 in the sterile water pretreated P.notoginseng was increased gradually after inoculation with F.solani, and the highest expression level was achieved at 48 h post inoculation.All the results of present study indicated that PnCHI1 was involved in defense response of P.notoginseng against the F.solani and A.panax.

A preliminary metagenomic study of puer tea during pile fermentation.

BACKGROUND: Up to now, there has been no report on the taxonomic and functional analysis of the microbial community in fermenting puer tea by pyrosequencing. In this study, metagenomic pyrosequencing was first used in fermenting puer tea to delineate a relatively comprehensive overview of the microbial taxonomy while also preliminarily characterising the functional ontologies of microbial genes present in puer tea pile fermentation. RESULTS: A total of 251 738 pyrosequencing reads (9197 contigs and 145 402 singletons) were generated by pyrosequencing. Taxonomic analysis revealed three dominant bacterial phyla, Actinobacteria (30.08%), Proteobacteria (24.47%) and Firmicutes (20.23%), and one dominant eukaryotic phylum, Ascomycota (15.21%) [corrected]. A total of 58 664 hits were categorised into 28 functional subsystems based on the SEED database. Moreover, two categories, 'metabolism of terpenoids and polyketides' and 'biosynthesis of other secondary metabolites', were selectively analysed and 69 enzyme genes were presented in 16 pathways. CONCLUSION: The dominant microbes of puer tea fermentation were bacteria in the present study, and yeasts rather than moulds accounted for the overwhelming majority of Eukaryota. The analysis of functional genes and metabolic pathways will be helpful for further study of the mechanism of puer tea fermentation at molecular level.

[The construction of over-expression vector for Panax notoginseng SS gene and its transformation].

PNS (Panax notoginseng saponins) is the main medical bioactive component in Panax notoginseng. The medical value of PNS cannot be extended because of its low production. With the deep study of saponins biosynthetic pathway, the control of PNS biosynthesis through metabolic engineering has gradually become possible. In this study, the Squalene synthase (SS) over-expression vector was established. By the way of agrobacterium-mediated method, the vector was transfered and integrated into the Panax notoginseng genome. The result of the PCR detection and the saponin content detection shows that over-expression SS is able to produce high level of Panax notoginseng saponins, and confirms the regulatory function of SS in the biosynthesis of ginsenosides in Panax notoginseng. It provides a theoretical basis and technical basis for the construction of PNS homologous or heterologous efficient expression system in the future.