Solanacearum Infection Research Articles

The FERONIA-RESPONSIVE TO DESSICATION 26 module regulates vascular immunity to Ralstonia solanacearum.

Some pathogens colonize plant leaves, but others invade the roots, including the vasculature, causing severe disease symptoms. Plant innate immunity has been extensively studied in leaf pathosystems; however, the precise regulation of immunity against vascular pathogens remains largely unexplored. We previously demonstrated that loss of function of the receptor kinase FERONIA (FER) increases plant resistance to the typical vascular bacterial pathogen Ralstonia solanacearum. Here, we show that upon infection with R. solanacearum, root xylem cell walls in Arabidopsis thaliana become highly lignified. FER is specifically upregulated in the root xylem in response to R. solanacearum infection, and inhibits lignin biosynthesis and resistance to this pathogen. We determined that FER interacts with and phosphorylates the transcription factor RESPONSIVE TO DESICCATION 26 (RD26), leading to its degradation. Overexpression and knockout of RD26 demonstrated that it positively regulates plant resistance to R. solanacearum by directly activating the expression of lignin-related genes. Tissue-specific expression of RD26 in the root xylem confirmed its role in vascular immunity. We confirmed that the FER-RD26 module regulates lignin biosynthesis and resistance against R. solanacearum in tomato (Solanum lycopersicum). Taken together, our findings unveil that the FER-RD26 cascade governs plant immunity against R. solanacearum in vascular tissues by regulating lignin deposition. This cascade may represent a key defense mechanism against vascular pathogens in plants.

Ralstonia solanacearum Infection Drives the Assembly and Functional Adaptation of Potato Rhizosphere Microbial Communities.

Bacterial wilt caused by Ralstonia solanacearum is a destructive disease that affects potato production, leading to severe yield losses. Currently, little is known about the changes in the assembly and functional adaptation of potato rhizosphere microbial communities during different stages of R. solanacearum infection. In this study, using amplicon and metagenomic sequencing approaches, we analyzed the changes in the composition and functions of bacterial and fungal communities in the potato rhizosphere across four stages of R. solanacearum infection. The results showed that R. solanacearum infection led to significant changes in the composition and functions of bacterial and fungal communities in the potato rhizosphere, with various microbial properties (including α,β-diversity, species composition, and community ecological functions) all being driven by R. solanacearum infection. The relative abundance of some beneficial microorganisms in the potato rhizosphere, including Firmicutes, Bacillus, Pseudomonas, and Mortierella, decreased as the duration of infection increased. Moreover, the related microbial communities played a significant role in basic metabolism and signal transduction; however, the functions involved in soil C, N, and P transformation weakened. This study provides new insights into the dynamic changes in the composition and functions of potato rhizosphere microbial communities at different stages of R. solanacearum infection to adapt to the growth promotion or disease suppression strategies of host plants, which may provide guidance for formulating future strategies to regulate microbial communities for the integrated control of soil-borne plant diseases.

Genome-wide analysis of the potato GRF gene family and their expression profiles in response to hormone and Ralstonia solanacearum infection.

Potato (Solanum tuberosum L.) is one of the most economically significant crops globally. Nevertheless, potato cultivation is becoming increasingly susceptible to a multitude of diseases, including bacterial wilt, which is caused by Ralstonia solanacearum. To identify the GRF gene family in potatoes and to examine their expression profiles in response to hormones and R. solanacearum infection. A comprehensive genome-wide analysis was conducted to identify the GRF gene family in the potato genome. A total of 13 GRF genes were identified from the latest potato genome, including five StGRFs belonging to the ɛ group and eight of the non-ɛ group. The transcriptional responses of the StGRFs to two biotic stress-related phytohormones (SA and MeJA) were defined, as well as the response to infection with R. solanacearum in a bacterial wilt-sensitive cultivar, S. tuberosum 'Qingshu 9'. Many StGRF genes exhibited high induction levels in response to R. solanacearum infection and SA treatment while displaying a marked decline in expression in the presence of MeJA. Furthermore, protein interaction network analysis revealed that the StGRF proteins interact with several candidate target proteins, indicating that GRF proteins are ubiquitous regulators in potatoes. However, the associations between two type III effectors (T3Es) RipAC/RipH2 from R. solanacearum isolates and StGRF7 were not detectable in a yeast two-hybrid assay. This study provides comprehensive information on the GRF gene family and lays a foundation for further research on the molecular mechanism of potato biotic stress adaptation.

CaZingipain2 Acts Positively in Pepper (Capsicum annuum L.) Immunity against R. solanacearum.

Bacterial wilt caused by Ralstonia solanacearum is one of the most important diseases in solanaceous plants, including peppers. It generally tends to be more serious under warm-temperature and moist (WM) conditions than at moist room-temperature (RM) conditions. Although immunity mechanisms at room temperature have been intensively studied, the mechanisms underlying WM conditions remain poorly understood. Herein, the pepper cysteine protease CaZingipain2 was expressed and functionally characterized in pepper immunity against R. solanacearum at WM conditions and at room temperature. The results showed that CaZingipain2 localized to the nucleus and was upregulated at the transcript level in pepper plants upon R. solanacearum infection under WM conditions (RSWM). Virus-induced gene silencing of CaZingipain2 significantly increased the susceptibility of pepper plants to RSWM, and was coupled with the downregulation of CaPRP1 and CaMgst3, which are specifically related to pepper immunity against RSWM, according to our previous studies, while its overexpression significantly reduced the susceptibility of N. benethamiana plants to RSWM compared to that of wild-type plants. In addition, our data showed that CaZingipain2 also acts positively in pepper immunity against R. solanacearum infection at room temperature by upregulating the SA- and JA-responsive PR genes, including CaNPR1 and CaDEF1. All these results indicate that CaZingipain2 improves pepper immunity against R. solanacearum under WM conditions and at room temperature by regulating different PR genes.

Dynamic transcription analysis reveals the underlying key mechanism of L-arabinose-enhanced tomato resistance to bacterial wilt

Tomato bacterial wilt caused by Ralstonia solanacearum is a serious economic soil-borne disease worldwide. L-arabinose (L-Ara) increases tomato resistance to bacterial wilt, but the resistance mechanism remains unclear. In this study, we conducted an RNA sequencing (RNA-seq) analysis of tomato root and stem that exhibited differential expression in response to R. solanacearum infection at 2 dpi and 5 dpi under L-Ara application. As a result, 797 and 5605 differentially expressed genes (DEGs) were identified in response to R. solanacearum infection at 2 dpi and 5 dpi, respectively. In particular, 4504 DEGs with 2501 up-regulated and 2001 down-regulated were presented in the stem at 5 dpi, specifying that most defense responses were expressed at the wilting stage. In the function analysis (GO and KEGG), the DEGs were primarily enriched in response to stress, cell wall, glutathione and phenylpropanoid biosynthesis and plant hormone signaling transduction. Among the DEGs, potential candidate genes related to plant hormone biosynthesis and signaling, phenylpropanoid biosynthesis, and cell wall metabolism were perceived. Furthermore, the transcription factors had high expression in ERF, bHLH, C2H2, MYB, NAC, WRKY, HD-ZIP, bZIP, MYB-related, and GRAS families. This research could provide theoretical support and valuable resources for further study of the prevention and control of bacterial wilt disease under L-Ara treatment .

CaWRKY22b Plays a Positive Role in the Regulation of Pepper Resistance to Ralstonia solanacearum in a Manner Associated with Jasmonic Acid Signaling.

As important transcription factors, WRKYs play a vital role in the defense response of plants against the invasion of multiple pathogens. Though some WRKY members have been reported to participate in pepper immunity in response to Ralstonia solanacearum infection, the functions of the majority of WRKY members are still unknown. Herein, CaWRKY22b was cloned from the pepper genome and its function against R. solanacearum was analyzed. The transcript abundance of CaWRKY22b was significantly increased in response to the infection of R. solanacearum and the application of exogenous methyl jasmonate (MeJA). Subcellular localization assay in the leaves of Nicotiana benthamiana showed that CaWRKY22b protein was targeted to the nuclei. Agrobacterium-mediated transient expression in pepper leaves indicated that CaWRKY22b overexpression triggered intensive hypersensitive response-like cell death, H2O2 accumulation, and the up-regulation of defense- and JA-responsive genes, including CaHIR1, CaPO2, CaBPR1, and CaDEF1. Virus-induced gene silencing assay revealed that knock-down of CaWRKY22b attenuated pepper's resistance against R. solanacearum and the up-regulation of the tested defense- and jasmonic acid (JA)-responsive genes. We further assessed the role of CaWRKY22b in modulating the expression of JA-responsive CaDEF1, and the result demonstrated that CaWRKY22b trans-activated CaDEF1 expression by directly binding to its upstream promoter. Collectively, our results suggest that CaWRKY22b positively regulated pepper immunity against R. solanacearum in a manner associated with JA signaling, probably by modulating the expression of JA-responsive CaDEF1.

CaMAPK1 Plays a Vital Role in the Regulation of Resistance to Ralstonia solanacearum Infection and Tolerance to Heat Stress.

As an important member of mitogen-activated protein kinase (MAPK) cascades, MAPKs play an important role in plant defense response against biotic and abiotic stresses; however, the involvement of the majority of the MAPK family members against Ralstonia solanacearum and heat stress (HS) remains poorly understood. In the present study, CaMAPK1 was identified from the genome of pepper and its function against R. solanacearum and HS was analyzed. The transcript accumulations of CaMAPK1 and the activities of its native promoter were both significantly induced by R. solanacearum inoculation, HS, and the application of exogenous hormones, including SA, MeJA, and ABA. Transient expression of CaMAPK1 showed that CaMAPK1 can be targeted throughout the whole cells in Nicotiana benthamiana and triggered chlorosis and hypersensitive response-like cell death in pepper leaves, accompanied by the accumulation of H2O2, and the up-regulations of hormones- and H2O2-associated marker genes. The knock-down of CaMAPK1 enhanced the susceptibility to R. solanacearum partially by down-regulating the expression of hormones- and H2O2-related genes and impairing the thermotolerance of pepper probably by attenuating CaHSFA2 and CaHSP70-1 transcripts. Taken together, our results revealed that CaMAPK1 is regulated by SA, JA, and ABA signaling and coordinates responses to R. solanacearum infection and HS in pepper.

Secondary Metabolites and Antioxidant Activity against Moko Disease as a Defense Mechanism of Musa spp. from the Ecuadorian Coast Area.

The Musa spp. represents the most commonly produced, transitioned, and consumed fruit around the globe, with several important applications in the biotechnology, pharmaceutical, and food industries. Moko disease is produced by Ralstonia solanacearum-a factor with a high impact on all crops in Ecuador, representing one of the biggest phytosanitary problems. Four of the most common varieties of Musa spp. were tested to identify the metabolic reaction of plants facing Moko disease. The phenolic and flavonoid content has been evaluated as a defense system, and the α-diphenyl-α-picrylhydrazyl free-radical-scavenging method (DPPH), free-radical-scavenging activity (ABTS), ferric-reducing antioxidant power (FRAP) assays, and liquid chromatography and mass spectrometry (LC-MS) have been adapted to analyze the active compounds with the antioxidant capacity necessary to counteract the pathogenic attack. Our results indicate that all the studied varieties of Musa spp. react in the same way, such that the diseased samples showed a higher accumulation of secondary metabolites with antioxidant capacity compared with the healthy ones, with high active compound synthesis identified during the appearance of Moko disease symptoms. More than 40 compounds and their derivatives (from kaempferol and quercetin glycosides) with protective roles demonstrate the implication of the Musa spp. defense system against R. solanacearum infection.

Expression patterns and evidence of the expansion of Nicotiana tabacum L. TALE genes in the Solanaceae family

AbstractThe three-amino-acid-loop-extension (TALE) proteins are a class of transcription factors that regulate meristem differentiation during plant growth and development. In this study, we identified a total of 45 members of the tobacco TALE (NtTALE) transcription factor family. Based on domain type, the NtTALE genes were divided into BELL subfamily and KNOX subfamily. Cis-acting element analysis showed that the NtTALE gene promoters had a variety of response elements, including light-responsive elements, hormonal and abiotic stresses responsive elements, plant development related elements. Among the 45 NtTALE genes, the expression patterns of various plant tissues at different stages were different, 10 responded to alkali stress, 19 responded to dehydration treatment, 14 responded to cold stress, two responded to salt stress, and 17 responded to Ralstonia solanacearum infection. Phylogenetic analysis showed that the number of TALE genes in Nicotiana was significantly expanded compared with that in other Solanaceae. The KNOXIII subfamily members (NtTALE29, NtTALE45) were found only in Nicotiana tabacum. This study provides a theoretical basis for further research on the biological function of NtTALE genes.

Transcriptome sequencing and expression analysis in peanut reveal the potential mechanism response to Ralstonia solanacearum infection

BackgroundBacterial wilt caused by Ralstonia solanacearum severely affects peanut (Arachis hypogaea L.) yields. The breeding of resistant cultivars is an efficient means of controlling plant diseases. Therefore, identification of resistance genes effective against bacterial wilt is a matter of urgency. The lack of a reference genome for a resistant genotype severely hinders the process of identification of resistance genes in peanut. In addition, limited information is available on disease resistance-related pathways in peanut.ResultsFull-length transcriptome data were used to generate wilt-resistant and -susceptible transcript pools. In total, 253,869 transcripts were retained to form a reference transcriptome for RNA-sequencing data analysis. Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis of differentially expressed genes revealed the plant-pathogen interaction pathway to be the main resistance-related pathway for peanut to prevent bacterial invasion and calcium plays an important role in this pathway. Glutathione metabolism was enriched in wilt-susceptible genotypes, which would promote glutathione synthesis in the early stages of pathogen invasion. Based on our previous quantitative trait locus (QTL) mapping results, the genes arahy.V6I7WA and arahy.MXY2PU, which encode nucleotide-binding site-leucine-rich repeat receptor proteins, were indicated to be associated with resistance to bacterial wilt.ConclusionsThis study identified several pathways associated with resistance to bacterial wilt and identified candidate genes for bacterial wilt resistance in a major QTL region. These findings lay a foundation for investigation of the mechanism of resistance to bacterial wilt in peanut.

Genome-wide identification of the TIFY gene family in tobacco and expression analysis in response to Ralstonia solanacearum infection

The TIFY gene family plays an essential role in plant development and abiotic and biotic stress responses. In this study, genome-wide identification of TIFY members in tobacco and their expression pattern analysis in response to Ralstonia solanacearum infection were performed. A total of 33 TIFY genes were identified, including the TIFY, PPD, ZIM&ZML and JAZ subfamilies. Promoter analysis results indicated that a quantity of light-response, drought-response, SA-response and JA-response cis-elements exist in promoter regions. The TIFY gene family exhibited expansion and possessed gene redundancy resulting from tobacco ploidy change. In addition, most NtTIFYs equivalently expressed in roots, stems and leaves, while NtTIFY1, NtTIFY4, NtTIFY18 and NtTIFY30 preferentially expressed in roots. The JAZ III clade showed significant expression changes after inoculation with R. solanacearum, and the expression of NtTIFY7 in resistant varieties, compared with susceptible varieties, was more stably induced. Furthermore, NtTIFY7-silenced plants, compared with the control plants, were more susceptible to bacterial wilt. These results lay a foundation for exploring the evolutionary history of TIFY gene family and revealing gene function of NtTIFYs in tobacco bacterial wilt resistance.

CaIAA2-CaARF9 module mediates the trade-off between pepper growth and immunity.

To challenge the invasion of various pathogens, plants re-direct their resources from plant growth to an innate immune defence system. However, the underlying mechanism that coordinates the induction of the host immune response and the suppression of plant growth remains unclear. Here we demonstrate that an auxin response factor, CaARF9, has dual roles in enhancing the immune resistance to Ralstonia solanacearum infection and in retarding plant growth by repressing the expression of its target genes as exemplified by Casmc4, CaLBD37, CaAPK1b and CaRROP1. The expression of these target genes not only stimulates plant growth but also negatively impacts pepper resistance to R. solanacearum. Under normal conditions, the expression of Casmc4, CaLBD37, CaAPK1b and CaRROP1 is active when promoter-bound CaARF9 is complexed with CaIAA2. Under R. solanacearum infection, however, degradation of CaIAA2 is triggered by SA and JA-mediated signalling defence by the ubiquitin-proteasome system, which enables CaARF9 in the absence of CaIAA2 to repress the expression of Casmc4, CaLBD37, CaAPK1b and CaRROP1 and, in turn, impeding plant growth while facilitating plant defence to R. solanacearum infection. Our findings uncover an exquisite mechanism underlying the trade-off between plant growth and immunity mediated by the transcriptional repressor CaARF9 and its deactivation when complexed with CaIAA2.

CaSTH2 disables CaWRKY40 from activating pepper thermotolerance and immunity against Ralstonia solanacearum via physical interaction.

CaWRKY40 coordinately activates pepper immunity against Ralstonia solanacearum infection (RSI) and high temperature stress (HTS), forms positive feedback loops with other positive regulators and is promoted by CaWRKY27b/CaWRKY28 through physical interactions; however, whether and how it is regulated by negative regulators to function appropriately remain unclear. Herein, we provide evidence that CaWRKY40 is repressed by a SALT TOLERANCE HOMOLOG2 in pepper (CaSTH2). Our data from gene silencing and transient overexpression in pepper and epoptic overexpression in Nicotiana benthamiana plants showed that CaSTH2 acted as negative regulator in immunity against RSI and thermotolerance. Our data from BiFC, CoIP, pull down, and MST indicate that CaSTH2 interacted with CaWRKY40, by which CaWRKY40 was prevented from activating immunity or thermotolerance-related genes. It was also found that CaSTH2 repressed CaWRKY40 at least partially through blocking interaction of CaWRKY40 with CaWRKY27b/CaWRKY28, but not through directly repressing binding of CaWRKY40 to its target genes. The results of study provide new insight into the mechanisms underlying the coordination of pepper immunity and thermotolerance.

Genome-wide analysis of the peanut CaM/CML gene family reveals that the AhCML69 gene is associated with resistance to Ralstonia solanacearum

BackgroundCalmodulins (CaMs)/CaM-like proteins (CMLs) are crucial Ca2+-binding sensors that can decode and transduce Ca2+ signals during plant development and in response to various stimuli. The CaM/CML gene family has been characterized in many plant species, but this family has not yet been characterized and analyzed in peanut, especially for its functions in response to Ralstonia solanacearum. In this study, we performed a genome-wide analysis to analyze the CaM/CML genes and their functions in resistance to R. solanacearum.ResultsHere, 67, 72, and 214 CaM/CML genes were identified from Arachis duranensis, Arachis ipaensis, and Arachis hypogaea, respectively. The genes were divided into nine subgroups (Groups I-IX) with relatively conserved exon‒intron structures and motif compositions. Gene duplication, which included whole-genome duplication, tandem repeats, scattered repeats, and unconnected repeats, produced approximately 81 pairs of homologous genes in the AhCaM/CML gene family. Allopolyploidization was the main reason for the greater number of AhCaM/CML members. The nonsynonymous (Ka) versus synonymous (Ks) substitution rates (less than 1.0) suggested that all homologous pairs underwent intensive purifying selection pressure during evolution. AhCML69 was constitutively expressed in different tissues of peanut plants and was involved in the response to R. solanacearum infection. The AhCML69 protein was localized in the cytoplasm and nucleus. Transient overexpression of AhCML69 in tobacco leaves increased resistance to R. solanacearum infection and induced the expression of defense-related genes, suggesting that AhCML69 is a positive regulator of disease resistance.ConclusionsThis study provides the first comprehensive analysis of the AhCaM/CML gene family and potential genetic resources for the molecular design and breeding of peanut bacterial wilt resistance.

Dynamic N6 -methyladenosine RNA modification regulates peanut resistance to bacterial wilt.

N6 -methyladenosine (m6 A) is the most abundant mRNA modification in eukaryotes and is an important regulator of gene expression as well as many other critical biological processes. However, the characteristics and functions of m6 A in peanut (Arachis hypogea L.) resistance to bacterial wilt (BW) remain unknown. Here, we analyzed the dynamic of m6 A during infection of resistant (H108) and susceptible (H107) peanut accessions with Ralstonia solanacearum (R. solanacearum), the causative agent of BW. Throughout the transcriptome, we identified 'URUAY' as a highly conserved motif for m6 A in peanut. The majority of differential m6 A located within the 3' untranslated region (UTR) of the transcript, with fewer in the exons. Integrative analysis of RNA-Seq and m6 A methylomes suggests the correlation between m6 A and gene expression in peanut R. solanacearum infection, and functional analysis reveals that m6 A-associated genes were related to plant-pathogen interaction. Our experimental analysis suggests that AhALKBH15 is an m6 A demethylase in peanut, leading to decreased m6 A levels and upregulation of the resistance gene AhCQ2G6Y. The upregulation of AhCQ2G6Y expression appears to promote BW resistance in the H108 accession.

The beneficial endophytic microbes enhanced tobacco defense system to resist bacterial wilt disease

BackgroundThe vital role of rhizosphere microbiome in protecting plants against pathogen infection has been well characterized. By contrast, beneficial effects of the plant endophytic microbiome and interactions with plants remain poorly understood. Here, we integrated microbial community analysis, culture-based methods and plant defense gene quantification to systematically investigate the responses of endophytic root and stem microbiomes and the defense system of the tobacco plant to Ralstonia solanacearum, a bacterial pathogen causing bacterial wilt disease worldwide.ResultsAn obvious reduction of community diversity and changes of microbial composition were observed in tobacco root and stem compartments upon R. solanacearum infection. Beneficial endophytic microbes were enriched in both diseased root and stem compartments, and beneficial microbes enriched in roots were more diverse than those in stems. Several beneficial bacteria enriched in diseased roots showed positive correlations with the pathogen abundance and exhibited great antagonistic activities against R. solanacearum. At the same time, the expression of key genes participating in plant defense signaling pathways and activities of plant defense enzymes were activated with R. solanacearum infection. Inoculation of beneficial endophyte Burkholderia ASV_550 in soils could greatly enhance the tobacco defense system in the presence of pathogen and decrease the disease incidence.ConclusionsThe recruited beneficial microbes exhibited an enhancement of the defense system of host plants. This work provides endophyte evidence for the “cry for help” strategy in plants and advances the current understanding of plant–microbe interactions in resisting plant disease.Graphical

Transcriptomics and virus-induced gene silencing identify defence-related genes during Ralstonia solanacearum infection in resistant and susceptible tobacco

Bacterial wilt (BW) caused by Ralstonia solanacearum is a globally prevalent bacterial soil-borne disease. In this study, transcriptome sequencing were subjected to roots after infection with the R. solanacearum in the resistant and susceptible tobacco variety. DEGs that responded to R. solanacearum infection in both resistant and susceptible tobacco contributed to pectinase and peroxidase development and were enriched in plant hormone signal transduction, signal transduction and MAPK signalling pathway KEGG terms. Core DEGs in the resistant tobacco response to R. solanacearum infection were enriched in cell wall, membrane, abscisic acid and ethylene terms. qRT-PCR indicated that Nitab4.5_0004899g0110, Nitab4.5_0004234g0080 and Nitab4.5_0001439g0050 contributed to the response to R. solanacearum infection in different resistant and susceptible tobacco. Silencing the p450 gene Nitab4.5_0001439g0050 reduced tobacco resistance to bacterial wilt. These results improve our understanding of the molecular mechanism of BW resistance in tobacco and solanaceous plants.

The tomato P69 subtilase family is involved in resistance to bacterial wilt.

The intercellular space or apoplast constitutes the main interface in plant-pathogen interactions. Apoplastic subtilisin-like proteases-subtilases-may play an important role in defence and they have been identified as targets of pathogen-secreted effector proteins. Here, we characterise the role of the Solanaceae-specific P69 subtilase family in the interaction between tomato and the vascular bacterial wilt pathogen Ralstonia solanacearum. R. solanacearum infection post-translationally activated several tomato P69s. Among them, P69D was exclusively activated in tomato plants resistant to R. solanacearum. In vitro experiments showed that P69D activation by prodomain removal occurred in an autocatalytic and intramolecular reaction that does not rely on the residue upstream of the processing site. Importantly P69D-deficient tomato plants were more susceptible to bacterial wilt and transient expression of P69B, D and G in Nicotiana benthamiana limited proliferation of R. solanacearum. Our study demonstrates that P69s have conserved features but diverse functions in tomato and that P69D is involved in resistance to R. solanacearum but not to other vascular pathogens like Fusarium oxysporum.

Uncovering the transcriptional responses of tobacco (Nicotiana tabacum L.) roots to Ralstonia solanacearum infection: a comparative study of resistant and susceptible cultivars

BackgroundTobacco bacterial wilt (TBW) caused by Ralstonia solanacearum is the most serious soil-borne disease of tobacco that significantly reduces crop yield. However, the limited availability of resistance in tobacco hinders breeding efforts for this disease.ResultsIn this study, we conducted hydroponic experiments for the root expression profiles of D101 (resistant) and Honghuadajinyuan (susceptible) cultivars in response to BW infection at 0 h, 6 h, 1 d, 3 d, and 7d to explore the defense mechanisms of BW resistance in tobacco. As a result, 20,711 and 16,663 (total: 23,568) differentially expressed genes (DEGs) were identified in the resistant and susceptible cultivars, respectively. In brief, at 6 h, 1 d, 3 d, and 7 d, the resistant cultivar showed upregulation of 1553, 1124, 2583, and 7512 genes, while the susceptible cultivar showed downregulation of 1213, 1295, 813, and 7735 genes. Similarly, across these time points, the resistant cultivar had downregulation of 1034, 749, 1686, and 11,086 genes, whereas the susceptible cultivar had upregulation of 1953, 1790, 2334, and 6380 genes. The resistant cultivar had more up-regulated genes at 3 d and 7 d than the susceptible cultivar, indicating that the resistant cultivar has a more robust defense response against the pathogen. The GO and KEGG enrichment analysis showed that these genes are involved in responses to oxidative stress, plant–pathogen interactions, cell walls, glutathione and phenylalanine metabolism, and plant hormone signal transduction. Among the DEGs, 239 potential candidate genes were detected, including 49 phenylpropane/flavonoids pathway-associated, 45 glutathione metabolic pathway-associated, 47 WRKY, 48 ERFs, eight ARFs, 26 pathogenesis-related genes (PRs), and 14 short-chain dehydrogenase/reductase genes. In addition, two highly expressed novel genes (MSTRG.61386-R1B-17 and MSTRG.61568) encoding nucleotide-binding site leucine-rich repeat (NBS-LRR) proteins were identified in both cultivars at 7 d.ConclusionsThis study revealed significant enrichment of DEGs in GO and KEGG terms linked to glutathione, flavonoids, and phenylpropane pathways, indicating the potential role of glutathione and flavonoids in early BW resistance in tobacco roots. These findings offer fundamental insight for further exploration of the genetic architecture and molecular mechanisms of BW resistance in tobacco and solanaceous plants at the molecular level.

Innate Root Exudates Contributed to Contrasting Coping Strategies in Response to Ralstonia solanacearum in Resistant and Susceptible Tomato Cultivars.

Tomato cultivars with contrasting resistance to pathogens regulate root exudates differentially in response to Ralstonia solanacearum attacks. However, strategies using innate root exudates against infection remain unknown. This study analyzed the innate root exudates of two tomato cultivars and their functions in regulating R. solanacearum infection. The innate root exudates differed between the two cultivars. Astaxanthin released from resistant plants inhibited colonization by R. solanacearum but promoted motility, while neferine released from susceptible plants suppressed motility and colonization. The secretion of astaxanthin in resistant tomatoes promoted the growth of biocontrol fungi in soil and reduced the abundance of pathogenic fungi. Neferine secreted by the susceptible cultivar inhibited the relative abundance of the bacterial-biocontrol-related Bacillus genus, indirectly reducing the soil's immune capacity. This study revealed contrasting strategies using root exudates in resistant and susceptible tomato cultivars to cope with R. solanacearum infection, providing a basis for breeding disease-resistant cultivars.