Virulence Biomarkers of Bursaphelenchus xylophilus: A Proteomic Approach

Unveiling the co-expression network and molecular targets behind rotenone resistance in the Bursaphelenchus xylophilus

Bursaphelenchus xylophilus is a pathogenic nematode responsible for pine wilt disease, which can cause the demise of pine trees and discoloration of trunks. As rotenone is an important botanical pesticide, its impact on B. xylophilus was investigated through RNA-seq to understand the response mechanism of nematode. The bioassay results yielded the 12-h LC30 (1.35 mg L-1) and LC50 (2.60 mg L-1) values for rotenone. Differential gene expression analysis identified 172 and 614 differentially expressed genes (DEGs) in B. xylophilus exposed to two different concentrations of rotenone (1.35 and 2.60 mg L-1). To validate these findings, the expression patterns of 10 DEGs were confirmed through RT-qPCR. Additionally, all DEGs were categorized into eight gene expression profiles using STEM. Notably, the gene ontology (GO) processes of "single-organism process," "metabolic process," and "catalytic activity" were prominently enriched in rotenone-treated samples, suggesting a role for metabolic and catalytic pathways in the nematode's response to rotenone stress. KEGG pathways related to "carbon metabolism," "drug metabolism-cytochrome P450," and "metabolism of xenobiotics by cytochrome P450" were similarly enriched, indicating potential mechanisms for detoxification resistance and oxidative stress resistance. The analysis pointed to the pivotal roles of detoxification- and oxidoreduction-related genes, as well as signal transduction-related genes, in enabling B. xylophilus to adapt to rotenone exposure. These insights could markedly enhance our understanding of nematode resistance mechanisms and potentially inform the development of more effective rotenone-based strategies for controlling B. xylophilus.

Detection Methods for Pine Wilt Disease: A Comprehensive Review

Pine wilt disease (PWD), caused by the nematode Bursaphelenchus xylophilus, is a highly destructive forest disease that necessitates rapid and precise identification for effective management and control. This study evaluates various detection methods for PWD, including morphological diagnosis, molecular techniques, and remote sensing. While traditional methods are economical, they are limited by their inability to detect subtle or early changes and require considerable time and expertise. To overcome these challenges, this study emphasizes advanced molecular approaches such as real-time polymerase chain reaction (RT-PCR), droplet digital PCR (ddPCR), and loop-mediated isothermal amplification (LAMP) coupled with CRISPR/Cas12a, which offer fast and accurate pathogen detection. Additionally, DNA barcoding and microarrays facilitate species identification, and proteomics can provide insights into infection-specific protein signatures. The study also highlights remote sensing technologies, including satellite imagery and unmanned aerial vehicle (UAV)-based hyperspectral analysis, for their capability to monitor PWD by detecting asymptomatic diseases through changes in the spectral signatures of trees. Future research should focus on combining traditional and innovative techniques, refining visual inspection processes, developing rapid and portable diagnostic tools for field application, and exploring the potential of volatile organic compound analysis and machine learning algorithms for early disease detection. Integrating diverse methods and adopting innovative technologies are crucial to effectively control this lethal forest disease.

Bursaphelenchus xylophilus Venom Allergen-Like Protein BxVAP1, Triggering Plant Defense-Related Programmed Cell Death, Plays an Important Role in Regulating Pinus massoniana Terpene Defense Responses

Bursaphelenchus xylophilus (pine wood nematode, PWN), a migratory plant-parasitic nematode, acts as an etiological agent, inflicting considerable damage to pine forests worldwide. Plant immunity constitutes a crucial factor in resisting various pathogenic invasions. The primary defensive responses of host pines against PWN infection encompass terpene accumulation, defense response-related gene expression, and programmed cell death. Venom allergen-like proteins (VAPs), as potential effectors, are instrumental in facilitating the successful colonization of PWNs. In this study, we investigated the inhibition of B. xylophilus VAP (BxVAP1) expression by RNA interference in vitro. Following BxVAP1 silencing, the reproduction rate and migration rate of the PWN population in Pinus massoniana decreased, the expression of the α-pinene synthase gene was induced, other terpene synthase and pathogenesis-related genes were inhibited and delayed, the peak times and levels of terpene-related substances were changed, and the degree of cavitation in P. massoniana was diminished. Transient expression of BxVAP1 in Nicotiana benthamiana revealed that BxVAP1 was expressed in both the cell membrane and nucleus, inducing programmed cell death and the expression of pathogen-associated molecular pattern-triggered immunity marker genes (NbAcre31 and NbPTI5). This study is the first to demonstrate that silencing the BxVAP1 gene affects host defense responses, including terpenoid metabolism in P. massoniana, and that BxVAP1 can be recognized by N. benthamiana as an effector to trigger its innate immunity, expanding our understanding of the parasitic mechanism of B. xylophilus.

Pine wilt disease: what do we know from proteomics?

Pine wilt disease (PWD) is a devastating forest disease caused by the pinewood nematode (PWN), Bursaphelenchus xylophilus, a migratory endoparasite that infects several coniferous species. During the last 20 years, advances have been made for understanding the molecular bases of PWN-host trees interactions. Major advances emerged from transcriptomic and genomic studies, which revealed some unique features related to PWN pathogenicity and constituted fundamental data that allowed the development of postgenomic studies. Here we review the proteomic approaches that were applied to study PWD and integrated the current knowledge on the molecular basis of the PWN pathogenicity. Proteomics has been useful for understanding cellular activities and protein functions involved in PWN-host trees interactions, shedding light into the mechanisms associated with PWN pathogenicity and being promising tools to better clarify host trees PWN resistance/susceptibility.

The Bursaphelenchus xylophilus candidate effector BxLip-3 targets the class I chitinases to suppress immunity in pine

Lipase is involved in lipid hydrolysis, which is related to nematodes' energy reserves and stress resistance. However, the role of lipases in Bursaphelenchus xylophilus, a notorious plant-parasitic nematode responsible for severe damage to pine forest ecosystems, remains largely obscure. Here, we characterized a class III lipase as a candidate effector and named it BxLip-3. It was transcriptionally up-regulated in the parasitic stages of B. xylophilus and specifically expressed in the oesophageal gland cells and the intestine. In addition, BxLip-3 suppressed cell death triggered by the pathogen-associated molecular patterns PsXEG1 and BxCDP1 in Nicotiana benthamiana, and its Lipase-3 domain is essential for immunosuppression. Silencing of the BxLip-3 gene resulted in a delay in disease onset and increased the activity of antioxidant enzymes and the expression of pathogenesis-related (PR) genes. Plant chitinases are thought to be PR proteins involved in the defence system against pathogen attack. Using yeast two-hybrid and co-immunoprecipitation assays, we identified two class I chitinases in Pinus thunbergii, PtChia1-3 and PtChia1-4, as targets of BxLip-3. The expression of these two chitinases was up-regulated during B. xylophilus inoculation and inhibited by BxLip-3. Overall, this study illustrated that BxLip-3 is a crucial virulence factor that plays a critical role in the interaction between B. xylophilus and host pine.

Proteomics research in forest trees: A 2012-2022 update

This review is a compilation of proteomic studies on forest tree species published in the last decade (2012-2022), mostly focused on the most investigated species, including Eucalyptus, Pinus, and Quercus. Improvements in equipment, platforms, and methods in addition to the increasing availability of genomic data have favored the biological knowledge of these species at the molecular, organismal, and community levels. Integration of proteomics with physiological, biochemical and other large-scale omics in the direction of the Systems Biology, will provide a comprehensive understanding of different biological processes, from growth and development to responses to biotic and abiotic stresses. As main issue we envisage that proteomics in long-living plants will thrive light on the plant responses and resilience to global climate change, contributing to climate mitigation strategies and molecular breeding programs. Proteomics not only will provide a molecular knowledge of the mechanisms of resilience to either biotic or abiotic stresses, but also will allow the identification on key gene products and its interaction. Proteomics research has also a translational character being applied to the characterization of the variability and biodiversity, as well as to wood and non-wood derived products, traceability, allergen and bioactive peptides identification, among others. Even thought, the full potential of proteomics is far from being fully exploited in forest tree research, with PTMs and interactomics being reserved to plant model systems. The most outstanding achievements in forest tree proteomics in the last decade as well as prospects are discussed.

Differential Impact of the Pinewood Nematode on Pinus Species Under Drought Conditions

The pinewood nematode (PWN), Bursaphelenchus xylophilus, responsible for the pine wilt disease (PWD), is a major threat to pine forests worldwide. Since forest mortality due to PWN might be exacerbated by climate, the concerns regarding PWD in the Mediterranean region are further emphasized by the projected scenarios of more drought events and higher temperatures. In this context, it is essential to better understand the pine species vulnerability to PWN under these conditions. To achieve that, physiological responses and wilting symptoms were monitored in artificially inoculated Pinus pinaster (P. pinaster), Pinus pinea (P. pinea), and Pinus radiata (P. radiata) saplings under controlled temperature (25/30°C) and water availability (watered/water stressed). The results obtained showed that the impact of PWN is species-dependent, being infected P. pinaster and P. radiata more prone to physiological and morphological damage than P. pinea. For the more susceptible species (P. pinaster and P. radiata), the presence of the nematode was the main driver of photosynthetic responses, regardless of their temperature or water regime conditions. Nevertheless, water potential was revealed to be highly affected by the synergy of PWN and the studied abiotic conditions, with higher temperatures (P. pinaster) or water limitation (P. radiata) increasing the impact of nematodes on trees' water status. Furthermore, water limitation had an influence on nematodes density and its allocation on trees' structures, with P. pinaster revealing the highest nematode abundance and inner dispersion. In inoculated P. pinea individuals, nematodes' population decreased significantly, emphasizing this species resistance to PWN. Our findings revealed a synergistic impact of PWN infection and stressful environmental conditions, particularly on the water status of P. pinaster and P. radiata, triggering disease symptoms and mortality of these species. Our results suggest that predicted drought conditions might facilitate proliferation and exacerbate the impact of PWN on these two species, through xylem cavitation, leading to strong changes in pine forests of the Mediterranean regions.

Novel Functional Analysis for Pathogenic Proteins of Bursaphelenchus xylophilus in Pine Seed Embryos Using a Virus Vector

Pine wilt disease (PWD), which is caused by the pine wood nematode Bursaphelenchus xylophilus, is among the most serious tree diseases worldwide. PWD is thought to be initiated by sequential excessive hypersensitive responses to B. xylophilus. Previous studies have reported candidate pathogenic molecules inducing hypersensitive responses in pine trees susceptible to B. xylophilus. The functions of some of these molecules have been analyzed in model plants using transient overexpression; however, whether they can induce hypersensitive responses in natural host pines remains unclear due to the lack of a suitable functional analysis method. In this study, we established a novel functional analysis method for susceptible black pine (Pinus thunbergii) seed embryos using transient overexpression by the Apple latent spherical virus vector and investigated five secreted proteins of B. xylophilus causing cell death in tobacco to determine whether they induce hypersensitive responses in pine. We found that three of five molecules induced significantly higher expression in pathogenesis-related genes ( p < 0.05), indicating hypersensitive response in pine seed embryos compared with mock and green fluorescence protein controls. This result suggests that tobacco-based screening may detect false positives. This study is the first to analyze the function of pathogenic candidate molecules of B. xylophilus in natural host pines using exogenous gene expression, which is anticipated to be a powerful tool for investigating the PWD mechanism.