Predicting the global potential distribution of Bursaphelenchus xylophilus using an ecological niche model: expansion trend and the main driving factors

Bursaphelenchus xylophilus (Steiner&Buhrer) Nickle is a global quarantine pest that causes devastating mortality in pine species. The rapid and uncontrollable parasitic spread of this organism results in substantial economic losses to pine forests annually. In this study, we used the MaxEnt model and GIS software ArcGIS10.8 to predict the distribution of B. xylophilus based on collected distribution points and 19 environmental variables (with a correlation coefficient of|R| > 0.8) for the contemporary period (1970-2000), 2041-2060 (2050s), 2061-2080 (2070s), and 2081-2100 (2090s) under four shared socioeconomic pathways (SSPs). We conducted a comprehensive analysis of the key environmental factors affecting the geographical distribution of B. xylophilus and suitable distribution areas. Our results indicate that in current prediction maps B. xylophilus had potential suitable habitats in all continents except Antarctica, with East Asia being the region with the most highly suitable areas and the most serious epidemic area currently. Precipitation of the warmest quarter, temperature seasonality, precipitation of the wettest month, and maximum temperature of the warmest month were identified as key environmental variables that determine the distribution of B. xylophilus. Under future climatic conditions, the potential geographic distribution of B. xylophilus will expand relative to current conditions. In particular, under the SSP5-8.5 scenario in 2081-2100, suitable areas will expand to higher latitudes, and there will be significant changes in suitable areas in Europe, East Asia, and North America. These findings are crucial for future prevention and control management and monitoring.

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.

Calcium stress reduces the reproductive capacity and pathogenicity of the pine wood nematode (Bursaphelenchus xylophilus) by inhibiting oxidative phosphorylation reaction

The continuous use of chemical pesticides to control nematodes could result in the developing of pesticide-resistant nematodes. Novel nucleic acid pesticides are becoming the focus of pesticide research due to their strong specificity, high efficiency, and environmental friendliness. However, the limited known biochemical targets restrict the development of target pesticides for nematodes. The calcium stress experiments on pine wood nematodes (PWN) showed that 100 mmol/L Ca2+ resulted in longitudinal depression on the PWN body wall, reduced oviposition, and increased corrected mortality. To enrich the biological targets of nematode pesticides, we further investigated the response mechanism of PWN to calcium stress at the molecular level. Differentially expressed gene analysis showed that genes involved in the oxidative phosphorylation (OXPHOS) pathway were significantly enriched. RNA interference results of 6 key genes belonging to four mitochondrial complex I (BXNDUFA2), III (BXQCR8), IV (BXCOX17), V (BXV-ATPaseB, BXV-ATPaseE, BXV-ATPaseε) in non-stressed nematodes showed reduction in PWN oviposition, population size, feeding ability, and pathogenicity. The BXNDUFA2 gene interference had the highest inhibitory impact by decreasing the oviposition from 31.00 eggs to 6.75 eggs and PWN population size from 8.27 × 103 nematodes to 1.64 × 103 nematodes, respectively. Interestingly, RNA interference of these 6 key genes in calcium-stressed nematodes also led to increased mortality and decreased oviposition of PWN. In summary, calcium stress inhibited the reproductive capacity of PWN by down-regulating key genes BXNDUFA2, BXQCR8, BXV-ATPaseB, BXV-ATPaseE, BXV-ATPaseε, and BXCOX17, thereby reducing the pathogenicity. The current results enrich the RNAi targets in PWN and provide a scientific basis for developing novel nucleic nematicides.

NTR-1's essential contribution to asymmetric mating between two sibling nematode Species: Bursaphelenchus xylophilus and B. Mucronatus

The pine-wood invasive species nematode Bursaphelenchus xylophilus causes great forestry damage globally, particularly in Eurasia. B. xylophilus can hybridize with its native sibling, Bursaphelenchus mucronatus, with whom it shares an interestingly asymmetric mating behavior. However, the molecular mechanism underlying interspecific asymmetric mating has yet to be clarified. ntr-1, a nematocin receptor gene, is involved in an oxytocin/vasopressin-like signaling system that can regulate reproduction. Structural analysis using bioinformatics revealed that both Bxy- and Bmu-ntr-1 encode 7TM-GPCR, a conserved sequence. In situ hybridization and qPCR showed that both Bxy- and Bmu-ntr-1 were highly expressed in adult nematodes. Specifically, Bxy-ntr-1 was expressed in the vulva of females and caudal gonad of males, whereas Bmu-ntr-1 was expressed in the postal vulva and uterus of females and the whole gonads of males. Furthermore, RNAi of ntr-1 further demonstrated the biological function of interspecific mating: ntr-1 can regulate mating behavior, lead to male-female specificity, and ultimately result in interspecific differences. In B. mucronatus, ntr-1 influenced male mating more than female mating success, while downregulation of ntr-1 in B. xylophilus resulted in a significant decline in the female mating rate. Competitive tests revealed that the mating rate of the cross significantly declined after downregulation of Bxy♀- and Bmu♂-ntr-1, but no obvious change occurred in the reciprocal cross. Thus, we speculate that ntr-1 may be the key factor behind interspecific asymmetric mating. The current study (1) demonstrated the regulatory function of ntr-1 on mating behavior and (2) theoretically revealed the molecular basis of interspecific asymmetric mating.

Application of dsRNA in the Pine Wood Nematode, Bursaphelenchus xylophilus

The pine wood nematode Bursaphelenchus xylophilus is one of the most destructive invasive species worldwide, causing the wilting and eventual death of pine trees. Despite recognition of their economic and environmental significance, it has thus far been impossible to study the detailed gene functions of plant parasitic nematodes through conventional forward genetics and transgenic methods. RNA interference (RNAi), as a reverse genetics technology, offers great convenience for studying the functional genes of nematodes, including B. xylophilus. We here outline a protocol for RNAi of the ppm-1 gene in B. xylophilus, which has been reported to play crucial roles in the development and reproduction of other pathogenic nematodes. For RNAi, the T7 promoter was linked to the 5'-terminal of the target fragment by polymerase chain reaction (PCR), and then double-stranded RNA (dsRNA) was synthesized by in vitro transcription. Subsequently, dsRNA delivery was accomplished by soaking nematodes with the dsRNA solution mixed with synthetic neurostimulants. Synchronized eggs, juveniles, and adults of B. xylophilus (approximately 20,000 individuals of each stage) were washed and soaked in dsRNA (0.8 μg/mL) with the soaking buffer for 24 h in the dark at 25 °C. The same quantity of nematodes was placed in the soaking buffer without dsRNA or with green fluorescent protein dsRNA as a control. After soaking, the expression level of the target transcripts was determined by real-time quantitative PCR. The effects of RNAi were then confirmed by microscopic observation of the phenotypes and comparison of the body size of adults among groups. The current protocol can help to progress research to understand the functions of the genes of B. xylophilus and other parasitic nematodes toward developing control strategies through genetic engineering.

DNA methylation on C5-Cytosine and N6-Adenine in the Bursaphelenchus xylophilus genome

BACKGROUND

The pinewood nematode is the causal agent of the pine wilt disease, which causes severe ecological and economic losses in coniferous forests. The invasion of pine wood nematode has undergone various rapid adaptations to a wide range of temperatures and to new hosts and vector insects. DNA methylation may play crucial roles in the rapid adaptation of PWN during invasion. However, whether the PWN genome contins functional DNA modifications remains elusive.

RESULTS

Here, we detected the extensive presence of 5-methylcytosine (5mC) and N6-methyladenine (6mA) in the B. xylophilus genome, with low methylation levels at most positions. Cytosines were methylated in the CpG, CHG. and CHH sequence contexts, with the lowest methylation levels at CpG sites. The methylation levels of CpG and 6mA in gene regions showed opposite trends. The changes in the abundance of 5mC and 6mA showed the same trends in response to temperature change, but opposite trends during development. Sequence and phylogenetic analyses showed that the proteins BxDAMT and BxNMAD have typical characteristics of a methylase and demethylase, respectively, and are conserved among species.

CONCLUSIONS

These findings shed light on the epigenetic modifications present in the genome of PWN, and will improve our understanding of its invasiveness and evolution.

Resistant and Susceptible Pinus thunbergii ParL. Show Highly Divergent Patterns of Differentially Expressed Genes during the Process of Infection by Bursaphelenchus xylophilus

Pine wilt disease (PWD) is a devastating disease that threatens pine forests worldwide, and breeding resistant pines is an important management strategy used to reduce its impact. A batch of resistant seeds of P. thunbergii was introduced from Japan. Based on the resistant materials, we obtained somatic plants through somatic embryogenesis. In this study, we performed transcriptome analysis to further understand the defense response of resistant somatic plants of P. thunbergii to PWD. The results showed that, after pine wood nematode (PWN) infection, resistant P. thunbergii stimulated more differential expression genes (DEGs) and involved more regulatory pathways than did susceptible P. thunbergii. For the first time, the alpha-linolenic acid metabolism and linoleic acid metabolism were intensively observed in pines resisting PWN infection. The related genes disease resistance protein RPS2 (SUMM2) and pathogenesis-related genes (PR1), as well as reactive oxygen species (ROS)-related genes were significantly up-expressed in order to contribute to protection against PWN inoculation in P. thunbergii. In addition, the diterpenoid biosynthesis pathway was significantly enriched only in resistant P. thunbergii. These findings provided valuable genetic information for future breeding of resistant conifers, and could contribute to the development of new diagnostic tools for early screening of resistant pine seedlings based on specific PWN-tolerance-related markers.

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.

Effect of electron beam irradiation on the pine wood nematode, Bursaphelenchus xylophilus

PURPOSE

Reproduction inhibition of the pine wood nematode (PWN) by electron beam (e-beam) irradiation both in vitro and in vivo was tested to determine if ionizing radiation could control the PWN by reducing survival and preventing reproduction, thus reducing the risk of pine wilt disease (PWD) spread.

MATERIALS AND METHODS

E-beam (10 MeV) irradiation treatment at different doses (0-4 kGy) was applied to PWNs in a Petri dish. Treatment of pine wood logs infested with PWNs was performed at 10 kGy. Mortality was determined by comparing the survival rates before and after irradiation treatment. DNA damage by e-beam irradiation (0-10 kGy) in the PWN was determined using the comet assay.

RESULTS

E-beam irradiation increased mortality and suppressed reproduction with increasing doses. The lethal dose (LD) values (kGy) were estimated as follows: LD50 = 2.32, LD90 = 5.03, and LD99 = 9.48. E-beam irradiation of pine wood logs significantly suppressed PWN reproduction. Comets of e-beam-irradiated cells showed an increased tail DNA level and moment with an increasing dose.

CONCLUSION

This study suggests that e-beam irradiation could be used as an alternative method for the management of pine wood logs infested with PWNs.

Two Novel Bursaphelenchus xylophilus Kunitz Effector Proteins Using Different Infection and Survival Strategies to Suppress Immunity in Pine

Pine wilt disease, caused by Bursaphelenchus xylophilus, results in tremendous economic loss in conifer production every year. To disturb the host immune responses, plant pathogens secrete a mass of effector proteins that facilitate the infection process. Although several effectors of B. xylophilus have been identified, detailed mechanisms of their functions remain largely unexplored. Here, we reveal two novel B. xylophilus Kunitz effectors, named BxKU1 and BxKU2, using different infection strategies to suppress immunity in Pinus thunbergii. We found that both BxKU1 and BxKU2 could suppress PsXEG1-triggered cell death and were present in the nucleus and cytoplasm in Nicotiana benthamiana. However, they had different three-dimensional structures and various expression patterns in B. xylophilus infection. In situ hybridization experiments showed that BxKU2 was expressed in the esophageal glands and ovaries, whereas BxKU1 was only expressed in the esophageal glands of females. We further confirmed that the morbidity was significantly decreased in P. thunbergii infected with B. xylophilus when BxKU1 and BxKU2 were silenced. The silenced BxKU2I, but not BxKU1, affected the reproduction and feeding rate of B. xylophilus. Moreover, BxKU1 and BxKU2 targeted to different proteins in P. thunbergii, but they all interacted with thaumatin-like protein 4 (TLP4) according to yeast two-hybrid screening. Collectively, our study showed that B. xylophilus could incorporate two Kunitz effectors in a multilayer strategy to counter immune response in P. thunbergii, which could help us better understand the interaction between plant and B. xylophilus.

Molecular Defense Response of Bursaphelenchus xylophilus to the Nematophagous Fungus Arthrobotrys robusta

Bursaphelenchus xylophilus causes pine wilt disease, which poses a serious threat to forestry ecology around the world. Microorganisms are environmentally friendly alternatives to the use of chemical nematicides to control B. xylophilus in a sustainable way. In this study, we isolated a nematophagous fungus-Arthrobotrys robusta-from the xylem of diseased Pinus massoniana. The nematophagous activity of A. robusta against the PWNs was observed after just 6 h. We found that B. xylophilus entered the trap of A. robusta at 24 h, and the nervous system and immunological response of B. xylophilus were stimulated by metabolites that A. robusta produced. At 30 h of exposure to A. robusta, B. xylophilus exhibited significant constriction, and we were able to identify xenobiotics. Bursaphelenchus xylophilus activated xenobiotic metabolism, which expelled the xenobiotics from their bodies, by providing energy through lipid metabolism. When PWNs were exposed to A. robusta for 36 h, lysosomal and autophagy-related genes were activated, and the bodies of the nematodes underwent disintegration. Moreover, a gene co-expression pattern network was constructed by WGCNA and Cytoscape. The gene co-expression pattern network suggested that metabolic processes, developmental processes, detoxification, biological regulation, and signaling were influential when the B. xylophilus specimens were exposed to A. robusta. Additionally, bZIP transcription factors, ankyrin, ATPases, innexin, major facilitator, and cytochrome P450 played critical roles in the network. This study proposes a model in which mobility improved whenever B. xylophilus entered the traps of A. robusta. The model will provide a solid foundation with which to understand the molecular and evolutionary mechanisms underlying interactions between nematodes and nematophagous fungi. Taken together, these findings contribute in several ways to our understanding of B. xylophilus exposed to microorganisms and provide a basis for establishing an environmentally friendly prevention and control strategy.

Functional analysis of 3 genes in xenobiotic detoxification pathway of Bursaphelenchus xylophilus against matrine

Bursaphelenchus xylophilus is the causative agent of pine wilt disease. It has caused devastating damage to ecosystems worldwide, owing to the characteristic of being widely spread and uncontrollable. However, the current methods of control are mainly based on pesticides, which can cause irreversible damage to the ecosystem. Therefore, the search for new drug targets and the development of environmentally friendly nematicides is especially valuable. In this study, three key genes of the xenobiotic detoxification pathways were cloned from B. xylophilus, which were subsequently subjected to bioinformatic analysis. The bioassay experiment was carried out to determine the concentration of matrine required for further tests. Subsequently, enzyme activity detection and three gene expression pattern analysis were performed on matrine treated nematodes. Finally, RNA interference was conducted to verify the functions carried out by the three genes in combating matrine. The results indicated that cytochrome P450 and glutathione S-transferase of B. xylophilus were activated by matrine, which induced high expression of BxCYP33C4, BxGST1, and BxGST3. After RNA interference of three genes of B. xylophilus, the sensitivity of B. xylophilus to matrine was increased and the survival rate of nematodes was reduced to various degrees in comparison to the control group. Overall, the results fully demonstrated that BxCYP33C4, BxGST1, and BxGST3 are valuable drug targets for B. xylophilus. Furthermore, the results suggested that matrine has value for development and exploitation in the prevention and treatment of B. xylophilus.

Three Phages from a Boreal Lake during Ice Cover Infecting Xylophilus, Caulobacter, and Polaromonas Species

Although the important role of microbes in freshwater is well understood, studies on phage-host systems in such environments during ice cover are completely lacking. Here, we describe the isolation and characterization of three new bacteriophages infecting Xylophilus sp., Caudobacter sp., and Polaromonas sp. from freshwater samples taken under the ice cover of Lake Konnevesi, Finland. Lumi, Kuura, and Tiera bacteriophages have tailed icosahedral virions and double-stranded DNA. Lumi is a siphophage with a genome of 80,496 bp, and Kuura and Tiera are podophages, and their genomes are 43,205 and 45,327 bp in length, resembling viruses in the class Caudoviricetes. Their host ranges were very limited among the winter-isolated bacterial strains from Konnevesi, each infecting only their own hosts. They can infect efficiently at 4 °C, showing that they are adapted to living in lake water under ice cover. Analysis of the viral genome sequences showed that a significant number of the gene products of each virus are unique, indicating that there is unexplored viral diversity in freshwaters. To our knowledge, Lumi and Tiera are the first phages isolated on the Xylophilus sp. and Polaromonas sp. strains, allowing their exploitation in further studies of freshwater bacterial-phage interactions.

Comprehensive Analysis and Functional Verification of the Pinus massoniana NBS-LRR Gene Family Involved in the Resistance to Bursaphelenchus xylophilus

Pinus massoniana Lamb. is a crucial timber and resin conifer in China, but its plantation industry is threatened by outbreaks of pine wilt disease (PWD) caused by Bursaphelenchus xylophilus (pinewood nematode; PWN). However, as of yet, there is no comprehensive analysis of NBS-LRR genes in P. massoniana involved in its defense against PWN. In this study, 507 NBS genes were identified in the transcriptome of resistant and susceptible P. masoniana inoculated with the PWN. The phylogenetic analysis and expression profiles of resistant and susceptible P. massoniana revealed that the up-regulated PmNBS-LRR97 gene was involved in conferring resistance to PWN. The results of real-time quantitative PCR (qRT-PCR) showed that PmNBS-LRR97 was significantly up-regulated after PWN infection, especially in the stems. Subcellular localization indicated that PmNBS-LRR97 located to the cell membrane. PmNBS-LRR97 significantly activated the expression of reactive oxygen species (ROS)-related genes in P. massoniana. In addition, the overexpression of PmNBS-LRR97 was capable of promoting the production of ROS, aiding in plant growth and development. In summary, PmNBS-LRR97 participates in the defense response to PWN and plays an active role in conferring resistance in P. massoniana. This finding provides new insight into the regulatory mechanism of the R gene in P. massoniana.

Expression of PmACRE1 in Arabidopsis thaliana enables host defence against Bursaphelenchus xylophilus infection

BACKGROUND

Pine wilt disease (PWD) is a destructive disease that endangers pine trees, resulting in the wilting, with yellowing and browning of the needles, and eventually the death of the trees. Previous studies showed that the Avr9/Cf-9 rapidly elicited (PmACRE1) gene was downregulated by Bursaphelenchus xylophilus infection, suggesting a correlation between PmACRE1 expression and pine tolerance. Here, we used the expression of PmACRE1 in Arabidopsis thaliana to evaluate the role of PmACRE1 in the regulation of host defence against B. xylophilus infection.

RESULTS

Our results showed that the transformation of PmACRE1 into A. thaliana enhanced plant resistance to the pine wood nematode (PWN); that is, the leaves of the transgenic line remained healthy for a longer period than those of the blank vector group. Ascorbate peroxidase (APX) activity and total phenolic acid and total flavonoid contents were higher in the transgenic line than in the control line. Widely targeted metabolomics analysis of the global secondary metabolites in the transgenic line and the vector control line showed that the contents of 30 compounds were significantly different between these two lines; specifically, the levels of crotaline, neohesperidin, nobiletin, vestitol, and 11 other compounds were significantly increased in the transgenic line. The studies also showed that the ACRE1 protein interacted with serine hydroxymethyltransferase, catalase domain-containing protein, myrosinase, dihydrolipoyl dehydrogenase, ketol-acid reductoisomerase, geranylgeranyl diphosphate reductase, S-adenosylmethionine synthase, glutamine synthetase, and others to comprehensively regulate plant resistance.

CONCLUSIONS

Taken together, these results indicate that PmACRE1 has a potential role in the regulation of plant defence against PWNs.

Functional Study on Cytochrome P450 in Response to L(-)-Carvone Stress in Bursaphelenchus xylophilus

Bursaphelenchus xylophilus (PWN) causes pine wilt disease (PWD), which is one of the most devastating pine diseases worldwide. Cytochrome P450 (CYP) catalyzes the biosynthetic metabolism of terpenoids and plays an important role in the modification of secondary metabolites in all living organisms. We investigated the molecular characteristics and biological functions of Bx-cyp29A3 in B. xylophilus. The bioinformatics analysis results indicated that Bx-cyp29A3 has a transmembrane domain and could dock with L(-)-carvone. The gene expression pattern indicated that Bx-cyp29A3 was expressed in 0.2, 0.4, 0.6, 0.8, and 1.0 mg/mL L(-)-carvone solutions. The Bx-cyp29A3 expression increased in a dose-dependent manner and peaked at 24 h of exposure when the L(-)-carvone solution concentration was 0.8 mg/mL. However, the gene expression peaked at 0.6 mg/mL after 36 h. Furthermore, RNA interference (RNAi) indicated that Bx-cyp29A3 played an essential role in the response to L(-)-carvone. The mortality rates of the Bx-cyp29A3 knockdown groups were higher than those of the control groups in the 0.4, 0.6, 0.8, and 1.0 mg/mL carvone solutions after 24 h of exposure or 36 h of exposure. In summary, bioinformatics provided the structural characteristics and conserved sequence properties of Bx-cyp29A3 and its encoded protein, which provided a target gene for the study of the P450 family of B. xylophilus. Gene silencing experiments clarified the function of Bx-cyp29A3 in the immune defense of B. xylophilus. This study provides a basis for the screening of new molecular targets for the prevention and management of B. xylophilus.

Identification of the Extracellular Nuclease Influencing Soaking RNA Interference Efficiency in Bursaphelenchus xylophilus

RNA interference (RNAi) efficiency dramatically varies among different nematodes, which impacts research on their gene function and pest control. Bursaphelenchus xylophilus is a pine wood nematode in which RNAi-mediated gene silencing has unstable interference efficiency through soaking in dsRNA solutions, the factors of which remain unknown. Using agarose gel electrophoresis, we found that dsRNA can be degraded by nematode secretions in the soaking system which is responsible for the low RNAi efficiency. Based on the previously published genome and secretome data of B. xylophilus, 154 nucleases were screened including 11 extracellular nucleases which are potential factors reducing RNAi efficacy. To confirm the function of nucleases in RNAi efficiency, eight extracellular nuclease genes (BxyNuc1-8) were cloned in the genome. BxyNuc4, BxyNuc6 and BxyNuc7 can be upregulated in response to dsGFP, considered as the major nuclease performing dsRNA degradation. After soaking with the dsRNA of nucleases BxyNuc4/BxyNuc6/BxyNuc7 and Pat10 gene (ineffective in RNAi) simultaneously for 24 h, the expression of Pat10 gene decreased by 23.25%, 26.05% and 11.29%, respectively. With soaking for 36 h, the expression of Pat10 gene decreased by 43.25% and 33.25% in dsBxyNuc6+dsPat10 and dsBxyNuc7+dsPat10 groups, respectively. However, without dsPat10, dsBxyNuc7 alone could cause downregulation of Pat10 gene expression, while dsBxyNuc6 could not disturb this gene. In conclusion, the nuclease BxyNuc6 might be a major barrier to the RNAi efficiency in B. xylophilus.

Molecular Defense Response of Pine Trees (Pinus spp.) to the Parasitic Nematode Bursaphelenchus xylophilus

Pine wilt disease (PWD) is a severe environmental problem in Eastern Asia and Western Europe, devastating large forest areas and causing significant economic losses. This disease is caused by the pine wood nematode (PWN), Bursaphelenchus xylophilus, a parasitic migratory nematode that infects the stem of conifer trees. Here we review what is currently known about the molecular defense response in pine trees after infection with PWN, focusing on common responses in different species. By giving particular emphasis to resistance mechanisms reported for selected varieties and families, we identified shared genes and pathways associated with resistance, including the activation of oxidative stress response, cell wall lignification, and biosynthesis of terpenoids and phenylpropanoids. The role of post-transcriptional regulation by small RNAs in pine response to PWN infection is also discussed, as well as the possible implementation of innovative RNA-interference technologies, with a focus on trans-kingdom small RNAs. Finally, the defense response induced by elicitors applied to pine plants before PWN infection to prompt resistance is reviewed. Perspectives about the impact of these findings and future research approaches are discussed.

Selenium nanoparticles are effective in penetrating pine and causing high oxidative damage to Bursaphelenchus xylophilus in pine wilt disease control

BACKGROUND

Research on selenium nanoparticles (SeNPs) in chemical defense and chemotherapy of plants has developed rapidly owing to their high microbial toxicity, environmental safety, and degradability. Pine wilt disease (PWD) threatens pine forests worldwide; however, it is difficult to kill the nematodes (Bursaphelenchus xylophilus) inside the tree that cause PWD using traditional pesticide formulations. SeNPs could be the key to controlling PWD.

RESULTS

In this study, approximately 50 nm SeNPs were prepared using a simple and green method, and chitosan was used to increase their biocompatibility and stability. The preparation and characterization results showed that the prepared SeNPs coated with chitosan (SeNPs@CS) were spherical and evenly dispersed. The bioassay results showed that SeNPs@CS had an LC₅₀ of 15.627 mg L^-1 against B. xylophilus. In addition, the killing mechanism of SeNPs@CS against B. xylophilus was studied. Confocal microscopy and transmission electron microscopy demonstrated that B. xylophilus were killed by reactive oxygen species, and the penetration of nano-form materials to B. xylophilus was higher than that of non-nano-form materials. To verify the effective penetration of SeNPs in pine tissues, Cy5-labeled SeNPs@CS was observed inside pine needles and branches using frozen sections and confocal microscopy. In addition, the cytotoxicity of SeO₂ and SeNPs@CS was tested, and the results showed that the cytotoxicity of SeNPs@CS to MC3T3-E1 cells was reduced.

CONCLUSION

These results show that SeNPs are expected to be used as a new strategy for the control of PWD with oxidative damage and high penetration to B. xylophilus and effective target penetration and biosafety. © 2022 Society of Chemical Industry.

Variations of Phyllosphere and Rhizosphere Microbial Communities of Pinus koraiensis Infected by Bursaphelenchus xylophilus

Pine wood nematode, Bursaphelenchus xylophilus, as one of the greatest threats to pine trees, is spreading all over the world. Plant microorganisms play an important role in the pathogenesis of nematodes. The phyllosphere and rhizosphere bacterial and fungal communities associated with healthy Pinus koraiensis (PKa) and P. koraiensis infected by B. xylophilus at the early (PKb) and last (PKc) stages were analyzed. Our results demonstrated that pine wood nematode (PWD) could increase the phyllosphere bacterial Pielou_e, Shannon, and Simpson index; phyllosphere fungal Chao 1 index, as well as rhizosphere bacterial Pielou_e, Shannon, and Simpson index; and rhizosphere fungal Pielou_e, Shannon, and Simpson index. What's more, slight shifts of the microbial diversity were observed at the early stage of infection, and the microbial diversity increased significantly as the symptoms of infection worsened. With the infection of B. xylophilus in P. koraiensis, Bradyrhizobium (rhizosphere bacteria), Massilia (phyllosphere bacteria), and Phaeosphaeriaceae (phyllosphere fungi) were the major contributors to the differences in community compositions among different treatments. With the infection of PWD, most of the bacterial groups tended to be co-excluding rather than co-occurring. These changes would correlate with microbial ability to suppress plant pathogen, enhancing the understanding of disease development and providing guidelines to pave the way for its possible management.

A Bursaphelenchus xylophilus Effector, BxSCD3, Suppresses Plant Defense and Contributes to Virulence

Bursaphelenchus xylophilus is the most economically important species of migratory plant-parasitic nematodes (PPNs) and causes severe damage to forestry in China. The successful infection of B. xylophilus relies on the secretion of a repertoire of effector proteins. The effectors, which suppress the host pine immune response, are key to the facilitation of B. xylophilus parasitism. An exhaustive list of candidate effectors of B. xylophilus was predicted, but not all have been identified and characterized. Here, an effector, named BxSCD3, has been implicated in the suppression of host immunity. BxSCD3 could suppress pathogen-associated molecular patterns (PAMPs) PsXEG1- and INF1-triggered cell death when it was secreted into the intracellular space in Nicotiana benthamiana. BxSCD3 was highly up-regulated in the early infection stages of B. xylophilus. BxSCD3 does not affect B. xylophilus reproduction, either at the mycophagous stage or the phytophagous stage, but it contributes to the virulence of B. xylophilus. Moreover, BxSCD3 significantly influenced the relative expression levels of defense-related (PR) genes PtPR-3 and PtPR-6 in Pinus thunbergii in the early infection stage. These results suggest that BxSCD3 is an important toxic factor and plays a key role in the interaction between B. xylophilus and host pine.

A Bursaphelenchus xylophilus pathogenic protein Bx-FAR-1, as potential control target, mediates the jasmonic acid pathway in pines

BACKGROUND

The pine wilt disease (PWD) caused by Bursaphelenchus xylophilus is a devastating forest disease and its pathogenesis remains unclear. Secreted enzymes and proteins are important pathogenicity determinants and Bx-FAR-1 is an important pathogenic protein involved in the interaction between pine and B. xylophilus. However, the function of the Bx-FAR-1 protein in monitoring and prevention PWD remains unknown.

RESULTS

We found a small peptide of B. xylophilus effector Bx-FAR-1 is sufficient for immunosuppression function in Nicotiana benthamiana. Transient expression of Bx-FAR-1 in N. benthamiana revealed that nuclear localization is required for its function. The results of the ligand binding test showed that Bx-FAR-1 protein had the ability to bind fatty acid and retinol. We demonstrated that Bx-FAR-1 targeted to the nuclei of Pinus thunbergii using the polyclonal antibody by immunologic approach. The content of jasmonic acid (JA) was significantly increased in P. thunbergii infected with B. xylophilus when Bx-FAR-1 was silenced. We identified an F-box protein as the host target of Bx-FAR-1 by yeast two-hybrid and co-immunoprecipitation. Moreover, we found that Pt-F-box-1 was up-regulated during B. xylophilus infection and the expression of Pt-F-box-1 was increased in Bx-FAR-1 double-stranded RNA (dsRNA)-treated host pines.

CONCLUSION

This study illustrated that Bx-FAR-1 might mediate the JA pathway to destroy the immune system of P. thunbergii, indicating that PWN likely secretes effectors to facilitate parasitism and promote infection, which could better reveal the pathogenesis mechanisms of B. xylophilus and would be beneficial for developing disease control strategies.

The Bursaphelenchus xylophilus effector BxML1 targets the cyclophilin protein (CyP) to promote parasitism and virulence in pine

BACKGROUND

Bursaphelenchus xylophilus is the causal agent of pine wilt disease (PWD) that has caused enormous ecological and economic losses in China. The mechanism in the interaction between nematodes and pine remains unclear. Plant parasitic nematodes (PPNs) secrete effectors into host plant tissues. However, it is poorly studied that role of effector in the infection of pine wood nematode (PWN).

RESULTS

We cloned, characterized and functionally validated the B. xylophilus effector BxML1, containing an MD-2-related lipid-recognition (ML) domain. This protein inhibits immune responses triggered by the molecular pattern BxCDP1 of B. xylophilus. An insitu hybridization assay demonstrated that BxML1 was expressed mainly in the dorsal glands and intestine of B. xylophilus. Subcellular localization analysis showed the presence of BxML1 in the cytoplasm and nucleus. Furthermore, number of B. xylophilus and morbidity of pine were significantly reduced in Pinus thunbergii infected with B. xylophilus when BxML was silenced. Using yeast two-hybrid (Y2H) and coimmunoprecipitation (CoIP) assays, we found that the BxML1 interacts with cyclophilin protein PtCyP1 in P. thunbergii.

CONCLUSIONS

This study illustrated that BxML1 plays a critical role in the B. xylophilus-plant interaction and virulence of B. xylophilus.

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.

Transcriptomics and coexpression network profiling of the effects of levamisole hydrochloride on Bursaphelenchus xylophilus

Bursaphelenchus xylophilus is one of the most dangerous forest pathogens in the world, causing devastating pine forest deaths with considerable economic losses. In this study, we investigated the B. xylophilus RNA sequence responses of two different concentrations of levamisole hydrochloride (LH). We observed that body-wall muscle twitching, paralysis and, ultimately, death. 2.5 mg/ml and 3.5 mg/ml LH have toxicological effects on B. xylophilus, with mortality increasing significantly with concentration (p < 0.05). RNA sequencing, differential gene expression analysis, and cluster analysis were performed, and 336, 384, 6 genes with significant variance in expression were identified. Gene Ontology annotation and Kyoto Encyclopedia of Genes and Genomes pathway analyses of the 12 intersecting genes revealed that these genes are mostly involved in metabolism of xenobiotics and have essential roles in drug sensitivity. Through the trend analysis of DEGs, it was divided into 8 modules, and the significant modules were selected to construct the co-expression network as the central genes of the drug metabolism-cytochrome P450 pathway (ko00982) and metabolism of xenobiotics by cytochrome P450 (ko00980). Eight highly related genes were identified, including cuticle collagen, cystathionine beta-synthase, endochitinase, pyruvate dehydrogenase E1 component subunit beta, aldehyde dehydrogenase, lipase, and zinc metalloproteinase. The expression levels of these genes were upregulated significantly at low concentrations and were significantly related to the resistance of B. xylophilus to LH. This study shows that B. xylophilus gene family expansions occurred in xenobiotic detoxification pathways through gene expression and potential horizontal correlated gene transfer with LH and helps to elucidate LH lethality and the evolutionary mechanisms underlying the adaptations of B. xylophilus to the environment. These results contributing to our understanding of B. xylophilus under LH and provide a data platform to providing a basis for its control.

Development of chitosan-coated nanoemulsions of two sulfides present in onion (Allium cepa) essential oil and their nematicidal activities against the pine wood nematode, Bursaphelenchus xylophilus

Pine wood nematode, Bursaphelenchus xylophilus, is a plant parasitic nematode which causes severe damage to several Pinus species. Two natural compounds, dipropyl trisulfide (DPTS) and methyl propyl trisulfide (MPTS), showed strong nematicidal activity against the pine wood nematode, presenting 4.24 and 17.81 μg/mL LC₅₀ values, respectively. However, hydrophobicity and low stability have limited their practical use in the field as nematicides. To overcome these problems, chitosan-coated nanoemulsions of DPTS and MPTS were developed. The optimum chitosan concentration for the delivery system of the two sulfides was 0.5%. Optimized chitosan-coated nanoemulsions of sulfides have a uniform size distribution (mean diameter = 203.7 and 207.7 nm, mean polydispersity index = 0.176 and 0.178) with sufficient colloidal stability (mean zeta potential = +40 and +45 mV). The LC₅₀ values of DPTS and MPTS nanoemulsions coated with 0.5% chitosan against the pine wood nematode were 5.01 and 16.60 μg/mL, respectively. In addition, chitosan coating improved the long-term storage stability and persistence of nematicidal activity of the nanoemulsions. This study indicates that the chitosan-coated nanoemulsion is a suitable formulation for sulfides as novel nematicides against the pine wood nematode for field application.

Bursaphelenchus xylophilus: An Important Pathogenic Factor of Pine Wilt Disease and Its Relationship with Bursaphelenchus mucronatus

Pine wilt disease is the most devastating pine disease caused by Bursaphelenchus xylophilus. Bursaphelenchus mucronatus is morphologically similar to B. xylophilus and geographically overlaps in its distribution. Although interspecific hybridization of the two nematodes has been performed in vitro, the dynamic regularity of hybrid formation and its risk in forests has not been well evaluated. In this study, a hybrid of B. xylophilus and Bursaphelenchus mucronatus mucronatus was identified in the laboratory and fields by molecular markers. The heterozygosity of ITS-5.8S loci for identification was unstable in the hybrid population, and the allele inherited from B. m. mucronatus was lost over several generations. We also provided evidence that hybrids existed in some new epidemic areas, while old epidemic areas were usually dominated by B. xylophilus. Hybrids could be generated when B. m. mucronatus was invaded by B. xylophilus, and the pathogenicity of the hybrids was similar to that of B. xylophilus. These findings may improve the understanding of the natural hybridization between B. xylophilus and B. m. mucronatus and pathogenic variation in pine wilt disease, providing new insights for future studies on disease detection, transmission, and quarantine.

Molecular characterization and functional analysis of multidrug resistance-associated genes of Pinewood nematode (Bursaphelenchus xylophilus) for nematicides

Bursaphelenchus xylophilus (Pinewood nematode, PWN) is the causative agent of pine wilt disease (PWD) which caused serious threat to pine forests in the world, especially in East Asia and Western Europe. At present, the control of PWD mainly rely on the massive use of pesticide despite the damage to human health and environmental safety. Developing novel drug targets is the optimized strategy for developing new method to control PWN. In this study, four multidrug resistance-associated protein (MRP) genes containing highly conserved MRP-associated domains were cloned from PWN. The expression patterns of the four Bx-mrps under three different nematicides treatments were studied by quantitative reverse transcription PCR (qRT-PCR) and the function of the four genes in multidrug resistance were also validated by RNA interference (RNAi). Results showed that the expression of Bx-mrp1, Bx-mrp2, Bx-mrp3, and Bx-mrp4 were significantly increased when exposed to different nematicides, wherein, Bx-mrp4 exposed by 4.0 mg/mL of matrine own the highest expression level. The mortality rates of Bx-mrps silenced nematodes revealed significant increase(P < 0.05)under matrine, avermectin, and emamectin benzoate exposure. Specially, Bx-mrp4 exposed with 4.0 mg/mL matrine for 24 h own the highest mortality increase by 18.34%. After RNAi of Bx-mrps, feeding ability of the nematodes were also significantly decreased. These results demonstrate that Bx-mrps were linked to the detoxification process and feeding behavior of PWN. Silencing of Bx-mrps can lead to increased sensitivity of PWN to nematicides and decrease its feeding ability. Bx-mrps are potential new PWN control targets in the future.

Nematicidal activity of teleocidin B4 isolated from Streptomyces sp. against pine wood nematode, Bursaphelenchus xylophilus

BACKGROUND

Pine wilt disease (PWD) is a plant disease that causes serious damage to pine trees. PWD occurs when the host plant is infected with pinewood nematode (PWN), Bursaphelenchus xylophilus. In this study, a compound with nematicidal activity was isolated from actinomycetes and its efficacy was investigated in vitro.

RESULT

We screened and selected Streptomyces sp. 680560, which had nematicidal activity against B. xylophilus. Based on 16S rRNA sequence analysis, it showed 99.93% similarity with Streptomyces blastmyceticus NRRB-5480^T . Furthermore, the active compound was isolated and identified as teleocidin B4. Teleocidin B4 at concentrations ranging from 6.25 to 100 μM had low nematicidal activity after 24 and 36 h against adult and stage juveniles (J2) of B. xylophilus, but after 48 h nematicidal activity exceeded 95%. The rate of inhibition of egg hatching for Teleocidin B4 6.25, 12.5, 25, 50, and 100 μM was confirmed to be dose-dependently inhibited after 48 h of treatment. Teleocidin B4 is not only toxic to hatched B. xylophilus, but also affects egg hatching.

CONCLUSION

This study was carried out to isolate actinomycete metabolites from pine tree endophytes from various natural environments for control of PWD. A compound with nematicidal activity was isolated from a selected strain and its structure was identified as teleocidin B4. The nematicidal effect of the isolated active substance, teleocidin B4, was confirmed. This is the first report of the effect of teleocidin B4 on B. xylophilus, suggesting its possibility as a PWD control agent. © 2020 Society of Chemical Industry.

Chitosan increases Pinus pinaster tolerance to the pinewood nematode (Bursaphelenchus xylophilus) by promoting plant antioxidative metabolism

The pine wilt disease (PWD), for which no effective treatment is available at the moment, is a constant threat to Pinus spp. plantations worldwide, being responsible for significant economic and environmental losses every year. It has been demonstrated that elicitation with chitosan increases plant tolerance to the pinewood nematode (PWN) Bursaphelenchus xylophilus, the causal agent of the PWD, but the biochemical and genetic aspects underlying this response have not been explored. To understand the influence of chitosan in Pinus pinaster tolerance against PWN, a low-molecular-weight (327 kDa) chitosan was applied to mock- and PWN-inoculated plants. Nematode population, malondialdehyde (MDA), catalase, carotenoids, anthocyanins, phenolic compounds, lignin and gene expression related to oxidative stress (thioredoxin 1, TRX) and plant defence (defensin, DEF, and a-farnesene synthase, AFS), were analysed at 1, 7, 14, 21 and 28 days post-inoculation (dpi). At 28 dpi, PWN-infected plants elicited with chitosan showed a sixfold lower nematode population when compared to non-elicited plants. Higher levels of MDA, catalase, carotenoids, anthocyanins, phenolic compounds, and lignin were detected in chitosan-elicited plants following infection. The expression levels of DEF gene were higher in elicited plants, while TRX and AFS expression was lower, possibly due to the disease containment-effect of chitosan. Combined, we conclude that chitosan induces pine defences against PWD via modulation of metabolic and transcriptomic mechanisms related with plant antioxidant system.

Nematotoxicity of a Cyt-like protein toxin from Conidiobolus obscurus (Entomophthoromycotina) on the pine wood nematode Bursaphelenchus xylophilus

BACKGROUND

The pine wood nematode Bursaphelenchus xylophilus is a destructive pest on Pinus trees and lacks effective control measures. The present study identified a novel nematotoxic cytolytic (Cyt)-like protein originating from the entomopathogenic fungus Conidiobolus obscurus.

RESULTS

The protein was successfully purified using heterologous expression in Escherichia coli and affinity chromatography. N-hydroxysuccinimide-rhodamine-labeled Cyt-like protein was used to establish the route of toxin uptake, and revealed that the toxin can enter the nematode via the stylet. In bioassays, the purified protein had high nematicide activity against B. xylophilus, with a median lethal concentration at 24 h of 15.8 and 29.4 μg mL^-1 for juveniles and adults, respectively. Compared with the deionized water control, fecundity, thrashing, and egg hatching were significantly reduced by 97%, 98%, and 83%, respectively, with 40 μg mL^-1 Cyt-like protein at 24-36 h. Staining with Oil-Red-O showed a decrease in large lipid droplet formation in the protein-treated adult nematodes.

CONCLUSION

The Cyt-like protein toxin possesses high nematicide activity against B. xylophilus with effects on nematode vitality and fecundity. The potential exists to use the Cyt-like protein for the control of B. xylophilus.

The role of mab-3 in spermatogenesis and ontogenesis of pinewood nematode, Bursaphelenchus xylophilus

BACKGROUND

Bursaphelenchus xylophilus is one of the most destructive invasive species, causing extensive economic losses worldwide. The sex ratio of female to male of B. xylophilus plays an important role in the nematode infestation. However, little is known about the processes of its sex determination. The double sex/mab-3-related family of transcription factors are highly conserved in animals, playing crucial roles in sex determination, spermatogenesis and ontogenesis. We therefore investigated its orthologue, Bxy-mab-3, in B. xylophilus.

RESULTS

Bxy-mab-3 has two typical conserved DNA-binding domains. It was observed in J2 (the second-stage of juveniles), J3, J4 and male adults (specifically on the spicules), but not in eggs or female adults via mRNA in situ hybridization. RNA-Seq indicated significantly higher expression in males. RNAi showed that the body size and sperm size of male adults were markedly smaller than those of the controls. Meanwhile, almost all the RNAi-treated males failed to mate with the normal females, even 26.34% of interfered males did not produce sperm. However, RNAi of Bxy-mab-3 had no effect on the sex ratio of B. xylophilus.

CONCLUSION

Bxy-mab-3 is indispensable for spermatogenesis, ontogenesis and mating behavior. It is a typical sex-determination gene with differential expression in males and females. However, knocking down Bxy-mab-3 expression could not alter the sex ratio as seen in other species. Our findings contribute towards a better understanding of the molecular events of Bxy-mab-3 in B. xylophilus, which provides promising hints for control of pine wilt disease by blocking ontogenesis and decreasing nematode fecundity.

Xylophilus rhododendri sp. nov., Isolated from Flower of Royal Azalea, Rhododendron schlippenbachii

A bacterial strain, designated CJ1-R5^T, was isolated from the flower of the royal azalea plant (Rhododendron schlippenbachii) collected in Jeju Island, Republic of Korea. The strain was a Gram-negative, strictly aerobic, motile, rod-shaped bacterium, growing at a temperature range of 4-33 °C (optimum 28-30 °C), pH 5.0-9.0 (optimum pH 7.0-8.0), and 0-1% NaCl (optimum 0%). The 16S rRNA sequence analysis of strain CJ1-R5^T revealed the highest sequence similarity (97.9%) with Xylophilus ampelinus ATCC 33914^T, and sequence similarities of less than 97.2% with other validly named species. Phylogenetic tree analysis based on the 16S rRNA gene sequences showed that strain CJ1-R5^T clustered with Xylophilus ampelinus ATCC 33914^T and two uncultured bacterial clones. The only quinone observed in strain CJ1-R5^T was ubiquinone-8. The polar lipids observed were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, one unidentified aminophospholipid and two unidentified lipids. The major fatty acids were C_16:0, C_17:0 cyclo, and summed feature 8 (C_18:1 ω7c and/or C_18:1 ω6c). The genome size of strain CJ1-R5^T was 5.85 Mbp. The genomic G + C content was 68.4 mol%. ANI and dDDH values between strain CJ1-R5^T and Xylophilus ampelinus ATCC 33914^T were 79.0% and 22.5%, respectively. Based on the polyphasic taxonomic data, strain CJ1-R5^T is considered to represent a novel species, for which the name Xylophilus rhododendri sp. nov. is proposed. The type strain is CJ1-R5^T (= KACC 21265^T = CCTCC AB2020030^T).