Thaumatin-Like Protein-1 Gene (Bx-tlp-1) Is Associated with the Pathogenicity of Bursaphelenchus xylophilus

Comparative Transcriptomic Analysis of Soybean Cyst Nematode Inbred Populations Non-adapted or Adapted on Soybean rhg1-a/Rhg4-Mediated Resistance

Soybean cyst nematode (SCN, Heterodera glycines) is most effectively managed through planting resistant soybean cultivars, but the repeated use of the same resistance sources has led to a widespread emergence of virulent SCN populations that can overcome soybean resistance. Resistance to SCN HG type 0 (Race 3) in soybean cultivar Forrest is mediated by an epistatic interaction between the soybean resistance genes rhg1-a and Rhg4. We previously developed two SCN inbred populations by mass-selecting SCN HG type 0 (Race 3) on susceptible and resistant recombinant inbred lines, derived from a cross between Forrest and the SCN-susceptible cultivar Essex, which differ for Rhg4. To identify SCN genes potentially involved in overcoming rhg1-a/Rhg4-mediated resistance, we conducted RNA sequencing on early parasitic juveniles of these two SCN inbred populations infecting their respective hosts, only to discover a handful of differentially expressed genes (DEGs). However, in a comparison with early parasitic juveniles of an avirulent SCN inbred population infecting a resistant host, we discovered 59 and 171 DEGs uniquely up- or downregulated in virulent parasitic juveniles adapted on the resistant host. Interestingly, the proteins coded by these 59 DEGs included vitamin B-associated proteins (reduced folate carrier, biotin synthase, and thiamine transporter) and nematode effectors known to play roles in plant defense suppression, suggesting that virulent SCN may exert a heightened transcriptional response to cope with enhanced plant defenses and an altered nutritional status of a resistant soybean host. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Dual functionality of pathogenesis-related proteins: defensive role in plants versus immunosuppressive role in pathogens

Plants respond to pathogen exposure by activating the expression of a group of defense-related proteins known as Pathogenesis-Related (PR) proteins, initially discovered in the 1970s. These PR proteins are categorized into 17 distinct families, denoted as PR1-PR17. Predominantly secreted, most of these proteins execute their defensive roles within the apoplastic space. Several PR proteins possess well-defined enzymatic functions, such as β-glucanase (PR2), chitinases (PR3, 4, 8, 11), proteinase (PR7), or RNase (PR10). Enhanced resistance against pathogens is observed upon PR protein overexpression, while their downregulation renders plants more susceptible to pathogen infections. Many of these proteins exhibit antimicrobial activity in vitro, and due to their compact size, some are classified as antimicrobial peptides. Recent research has unveiled that phytopathogens, including nematodes, fungi, and phytophthora, employ analogous proteins to bolster their virulence and suppress plant immunity. This raises a fundamental question: how can these conserved proteins act as antimicrobial agents when produced by the host plant but simultaneously suppress plant immunity when generated by the pathogen? In this hypothesis, we investigate PR proteins produced by pathogens, which we term "PR-like proteins," and explore potential mechanisms by which this class of virulence factors operate. Preliminary data suggests that these proteins may form complexes with the host's own PR proteins, thereby interfering with their defense-related functions. This analysis sheds light on the intriguing interplay between plant and pathogen-derived PR-like proteins, providing fresh insights into the intricate mechanisms governing plant-pathogen interactions.

Transcriptome Study of Bursaphelenchus xylophilus Treated with Fomepizole Reveals a Serine/Threonine-Protein Phosphatase Gene that Is Substantially Linked with Vitality and Pathogenicity

Bursaphelenchus xylophilus, the pine wood nematode (PWN), is the causal agent of pine wilt disease (PWD), which causes enormous economic loss annually. According to our previous research, fomepizole, as a selective inhibitor of PWN alcohol dehydrogenase (ADH), has the potential to be a preferable lead compound for developing novel nematicides. However, the underlying molecular mechanism is still unclear. The result of molecular docking showed that the stronger interactions between fomepizole and PWN ADH at the active site of ADH were attributed to hydrogen bonds. Low-dose fomepizole had a substantial negative impact on the egg hatchability, development, oviposition, and lifespan of PWN. Transcriptome analysis indicated that 2,124 upregulated genes and 490 downregulated genes in fomepizole-treated PWN were obtained. Kyoto Encyclopedia of Genes and Genomes enrichment analysis of differentially expressed genes indicated that fomepizole could be involved in controlling PWN vitality mainly by regulating key signaling pathways, such as the ribosome, hippo signaling pathway, and lysosome. Remarkably, the results of RNA interference indicated that the downregulated serine/threonine-protein phosphatase gene (stpp) could reduce the egg hatchability, development, oviposition, and lifespan of PWN, which was closely similar to the consequences of nematodes with low-dose fomepizole treatment. In addition, the silencing of stpp resulted in weakness of PWN pathogenicity, which indicated that stpp could be a potential drug target to control PWN.

Transcriptomic response of Pinus massoniana to infection stress from the pine wood nematode Bursaphelenchus xylophilus

The pinewood nematode (PWN) Bursaphelenchus xylophilus is a forestry quarantine pest and causes an extremely dangerous forest disease that is spreading worldwide. Due to the complex pathogenic factors of pine wood nematode disease, the pathogenesis is still unknown. B. xylophilus ultimately invades a host and causes death. However, little is known about the defence-regulating process of host pine after infection by B. xylophilus at the molecular level. Therefore, we wanted to understand how Pinus massoniana regulates its response to invasion by B. xylophilus. P. massoniana were artificially inoculated with B. xylophilus solution, while those without B. xylophilus solution were used as controls. P. massoniana inoculated with B. xylophilus solution for 0 h, 6 h, 24 h, and 120 h was subjected to high-throughput sequencing to obtain transcriptome data. At various time points (0 h, 6 h, 24 h, 120 h), gene transcription was measured in P. massoniana inoculated with PWN. At different time points, P. massoniana gene transcription differed significantly, with a response to early invasion by PWN. According to Gene Ontology (GO) classification and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis, P. massoniana response to PWN invasion involves a wide range of genes, including plant hormone signal transformation, flavonoid biosynthesis, amino sugar and nucleoside sugar metabolism, and MAPK signalling pathways. Among them, inoculation for 120 hours had the greatest impact on differential genes. Subsequently, weighted gene coexpression network analysis (WGCNA) was used to analyse transcriptional regulation of P. massoniana after PWN infection. The results showed that the core gene module of P. massoniana responding to PWN was "MEmagenta", enriched in oxidative phosphorylation, amino sugar and nucleotide sugar metabolism, and the MAPK signalling pathway. MYB family transcription factors with the highest number of changes between infected and healthy pine trees accounted for 20.4% of the total differentially expressed transcription factors. To conclude, this study contributes to our understanding of the molecular mechanism of initial PWN infection of P. massoniana. Moreover, it provides some important background information on PWN pathogenic mechanisms.

Comprehensive Analysis of Copy Number Variations on Glycoside Hydrolase 45 Genes among Different Bursaphelenchus xylophilus Strains

Bursaphelenchus xylophilus is considered the most dangerous quarantine pest in China. It causes enormous economic and ecological losses in many countries from Asia and Europe. The glycoside hydrolase 45 gene family has been demonstrated in early studies to contribute to the cell wall degradation ability of B. xylophilus during its infection. However, the copy number variation (CNV) of the GH45 gene and its association with B. xylophilus pathogenicity were not fully elucidated. In this study, we found that the GH45 gene with two copies is the most predominant type among 259 B. xylophilus strains collected from China and Japan. Additionally, 18 strains are identified as GH45 genes with a single copy, and only two strains are verified to have three copies. Subsequent expression analysis and inoculation test suggest that the copy numbers of the GH45 gene are correlated with gene expression as well as the B. xylophilus pathogenicity. B. xylophilus strains with more copies of the GH45 gene usually exhibit more abundant expression and cause more severe wilt symptoms on pine trees. The aforementioned results indicated the potential regulatory effects of CNV in B. xylophilus and provided novel information to better understand the molecular pathogenesis of this devastating pest.

Genes Encoding Potential Molecular Mimicry Proteins as the Specific Targets for Detecting Bursaphelenchus xylophilus in PCR and Loop-Mediated Isothermal Amplification Assays

The introduction of the pine wood nematode (Bursaphelenchus xylophilus) to new areas has affected the international forestry industry because this pathogen causes pine wilt disease (PWD). Therefore, methods for the accurate and reliable detection of B. xylophilus are essential for controlling and managing this pest. The PCR and Loop-Mediated Isothermal Amplification (LAMP) techniques developed in this study involve species-specific primer sets targeting B. xylophilus genes encoding potential molecular mimicry proteins (Bx-tlp-1, Bx-tlp-2, and Bx-cpi), which are associated with pathogenicity. The PCR and LAMP results revealed that the primers were specific for B. xylophilus Bx-tlp-1, Bx-tlp-2, and Bx-cpi. Moreover, our LAMP assay targeting Bx-tlp-1 conducted at 63°C detected B. xylophilus within 20 min and B. xylophilus from Monochamus alternatus or M. saltuarius within 30 min. The lower limits of detection for the LAMP and PCR assays were 10 pg and 10 ng genomic DNA, respectively, implying these assays may be useful for the rapid detection of B. xylophilus in pine forests. Designing primers specific for Bx-tlp-1, Bx-tlp-2, and Bx-cpi enabled the relatively rapid detection of B. xylophilus isolates as well as M. alternatus or M. saltuarius carrying B. xylophilus. These primers, which were designed following a thorough functional analysis of key B. xylophilus pathogenicity-related genes, may be useful for developing improved assays for the early diagnosis and prevention of PWD.

Expression of the Thaumatin-Like Protein-1 Gene (Bx-tlp-1) from Pine Wood Nematode Bursaphelenchus xylophilus Affects Terpene Metabolism in Pine Trees

Pine wilt disease is a major forest disease worldwide, including in China, where it has severely damaged pine forest ecosystems, and the pathogen is pine wood nematode (Bursaphelenchus xylophilus). The thaumatin-like protein-1 gene (Bx-tlp-1) is a key gene associated with B. xylophilus pathogenicity, which is also responsive to α-pinene. In this study, an examination of Pinus massoniana seedlings infected by B. xylophilus revealed that monoterpene (sesquiterpene) levels peaked on days 15 and 27 (days 18 and 27). Meanwhile, P. massoniana Pm-tlp expression levels were high on days 3, 12, and 27, which were consistent with the expression of key enzymes genes in the terpene biosynthesis pathway. The functional similarity of B. xylophilus Bx-TLP-1 and P. massoniana Pm-TLP suggests Bx-TLP-1 and Pm-TLP may have similar roles in P. massoniana. There was also no secondary accumulation of terpenes in P. massoniana seedlings during B. xylophilus treated with dsRNA targeting Bx-tlp-1 (dsTLP1) infections, reflecting the decreased pathogenicity of B. xylophilus and the delayed disease progression in pine trees. And the results of micro-CT showed that the degree of cavitation for the trees inoculated with Bx-TLP-1 (0.3811 mm³) was greater than that for the trees inoculated with dsTLP1 PWNs (0.1204 mm³) on day 15 after inoculation. Results from this study indicated that B. xylophilus Bx-tlp-1 gene may induce the upregulated expression of related genes encoding enzymes in the terpene synthesis pathway of P. massoniana, resulting in the accumulation of terpenes, which also provided an insight to investigate the B. xylophilus pathogenicity in the future.

Characterization and expression of a novel thaumatin-like protein (CcTLP1) from papaveraceous plant Corydalis cava

Thaumatin-like proteins (TLPs, osmotins) form a protein family which shares a significant sequence homology to the sweet-tasting thaumatin from the plant Thaumatococcus daniellii. TLPs are not sweet-tasting and are involved in response to biotic stresses and developmental processes. Recently it has been shown using a proteomic approach that the tuber extract from Corydalis cava (Papaveraceae) contains a TLP protein. The aim of this work was to characterize the structure and expression of TLP from C. cava tubers. The results obtained using a PCR approach with degenerate primers demonstrated a coding sequence of a novel protein, named CcTLP1. It consists of 225 aa, has a predicted molecular weight of 24.2 kDa (NCBI GenBank accession no. KJ513303) and has 16 strictly conserved cysteine residues, which form 8 disulfide bridges and stabilize the 3D structure. CcTLP1 may be classified into class IX of plant TLPs. The highest CcTLP1 expression levels were shown by qPCR in the stem of the plant compared to other organs and in the medium-size plants compared to other growth phases. The results confirm that CcTLP1 is expressed during plant growth and development until flowering, with a possible defensive function against different stress conditions.

Thaumatin-like proteins and a cysteine protease inhibitor secreted by the pine wood nematode Bursaphelenchus xylophilus induce cell death in Nicotiana benthamiana

Pine wilt disease (PWD) is an infectious disease of pines that typically kills affected trees. The causal pathogen of PWD is the pine wood nematode (PWN), Bursaphelenchus xylophilus. Understanding of the disease has advanced in recent years through the use of a highly sensitive proteomics procedure and whole genome sequence analysis; in combination, these approaches have enabled identification of proteins secreted by PWNs. However, the roles of these proteins during the onset of parasitism have not yet been elucidated. In this study, we used a leaf-disk assay based on transient overexpression in Nicotiana benthamiana to allow functional screening of 10 candidate pathogenic proteins secreted by PWNs. These proteins were selected based on previous secretome and RNA-seq analyses. We found that five molecules induced significant cell death in tobacco plants relative to a GFP-only control. Three of these proteins (Bx-TH1, Bx-TH2, and Bx-CPI) may have a role in molecular mimicry and likely make important contributions to inducing hypersensitive responses in host plants.

Potential Molecular Mimicry Proteins Responsive to α-pinene in Bursaphelenchus xylophilus

: Bursaphelenchus xylophilus is a nematode species that has damaged pine trees worldwide, but its pathogenesis has not been fully characterized. α-pinene helps protect host species during the early B. xylophilus infection and colonization stages. In this study, we identified potential molecular mimicry proteins based on a comparative transcriptomic analysis of B. xylophilus. The expression levels of three genes encoding secreted B. xylophilus proteins were influenced by α-pinene. We cloned one gene encoding a thaumatin-like protein, Bx-tlp-2 (accession number MK000287), and another gene encoding a cysteine proteinase inhibitor, Bx-cpi (accession number MK000288). Additionally, α-pinene appeared to induce Bx-tlp-1 expression, but had the opposite effect on Bx-cpi expression. An analysis of the expression of the potential molecular mimicry proteins in B. xylophilus infecting pine trees revealed that the α-pinene content was consistent with the expression levels of Bx-tlp-1 (Bx-cpi) and Pm-tlp (Pm-cpi) over time. Thus, these genes likely have important roles contributing to the infection of pine species by B. xylophilus. The results of this study may be relevant for future investigations of the functions of Bx-tlp-1, Bx-tlp-2 and Bx-cpi, which may provide a point to explore the relationship between B. xylophilus and host pines.