Search

Pakistan's economy greatly benefits from citrus production since these fruits are sold and consumed all over the world. Although citrus fruits are easy to cultivate, they are susceptible to diseases caused by bacteria, viruses, and fungi. These challenges, as well as difficulties in obtaining the proper nutrients, might negatively impact fruit yields and quality. Citrus canker is another complicated problem caused by the germ Xanthomonas axonopodis. This germ affects many types of citrus fruits all over the world. This study looked closely at how citrus canker affects the leaves and the quality of the fruit in places like Sargodha, Bhalwal, Kotmomin, and Silanwali, which are big areas for growing citrus in the Sargodha district. What we found was that plants without the disease had more chlorophyll in their leaves compared to the sick plants. Also, the healthy plants had better amounts of important minerals like calcium, magnesium, potassium, and phosphorus in their fruits. But the fruits with the disease had too much sodium, and the iron levels were a bit different. The fruits with the disease also didn't have as much of something that protects them called antioxidants, which made them more likely to get sick. This study helps us understand how citrus canker affects plants and fruit, so we can think of ways to deal with it., (© 2024. The Author(s).)

Key Message: MeRAVs positively regulate ROS burst and the expression of downstream disease resistance-related genes, which underlie improved disease resistance to Xam. Cassava (Manihot esculenta Crantz) is an important food crop and energy crop, but its yield is seriously affected by cassava bacterial blight (CBB) caused by Xanthomonas axonopodis pv. manihotis (Xam). Related to ABI3/VP1 (RAV) transcription factor family belongs to the APETALA2/Ethylene-Responsive Factor (AP2/ERF) family, which plays an important role in plant growth, development and response to biotic and abiotic stresses. In this study, we found that MeRAVs positively co-regulates the resistance to Xam and stimulates the innate immune response by regulating reactive oxygen species (ROS) burst in cassava. Dual-luciferase assay showed that seven MeRAVs exhibited transcriptional activate activity by binding CAACA motif and CACCTG motif. A large number of differentially expressed genes (DEGs) were identified through RNA-seq analysis of MeRAVs-silenced lines, and the DEGs co-regulated by seven MeRAVs accounted for more than 45% of the total DEGs. In addition, seven MeRAVs positively regulate expression of disease resistance-related genes through directly binding to their promoters. In summary, MeRAVs co-regulate ROS burst and the expression of downstream disease resistance-related genes, which underlie improved disease resistance to Xam., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Xanthomonas axonopodis pv. punicae (Xap), the bacterial blight pathogen of pomegranate, incurs substantial loss to yield and reduces export quality of this economically important fruit crop. During infection, the bacterium secretes six non-TAL (Xop) effectors into the pomegranate cells through a specialized type three secretion system (T3SS). Previously, we demonstrated the role of two key effectors, XopL and XopN in pathogenesis. Here, we investigate the role of rest effectors (XopC2, XopE1, XopQ and XopZ) on disease development. We generated null mutants for each individual effector and mutant bacterial suspension was infiltrated into pomegranate leaves. Compared to Xap wild, the mutant bacterial growth was reduced by 2.7-11.5 folds. The mutants produced lesser water-soaked lesions when infiltrated on leaves by 1.13-2.21 folds. Among the four effectors, XopC2 contributes highest for in planta bacterial growth and disease development. XopC2 efficiently suppressed the defense responses like callose deposition, reactive oxygen species (ROS) and the activation of immune responsive genes. Being a major contributor, we further characterize XopC2 for its subcellular localization, its protein structure and networking. XopC2 is localized to the plasma membrane of Nicotiana benthamiana like XopL and XopN. XopC2 is a 661 amino acids protein having 15 alpha and 17 beta helix. Our STRING and I-TASSER based analysis hinted that XopC2 interacts with multiple membrane localized plant proteins including transcription regulator of CCR4-NOT family, TTN of maintenance of chromosome family and serine/threonine-protein phosphatase 2A (PP2A) isoform. Based on the interaction it is predicted that XopC2 might involve in diverse functions like nuclear-transcribed mRNA catabolic process, maintenance of chromosome, hormone signaling and protein dephosphorylation activities and thereby suppress the plant immunity. Altogether, our study suggests that Xap largely depends on three non-TAL (Xop) effectors, including XopC2, XopL and XopN, to modulate pomegranate PTI for its unrestricted proliferation during bacterial blight development., (Copyright © 2020 Elsevier GmbH. All rights reserved.)

Methyltransferases (MTases) are enzymes that modify specific substrates by adding a methyl group using S-adenosyl-l-methionine. Functions of MTases have been extensively studied in eukaryotic organisms and animal pathogenic bacteria. Despite their importance, mechanisms underlying MTase function in plant pathogenic bacteria have not been studied in depth, as is the case of Xanthomonas axonopodis pv. glycines (Xag) that causes bacterial pustule disease in soybean crops worldwide. Here, the association between Xag proteome alterations and three MTase-overexpressing strains, Xag(XgMT1), Xag(XgMT2), and Xag(XgMT3), compared to Xag carrying an empty vector, Xag(EV) is reported. Using label-free shotgun comparative proteomic analysis, proteins are identified in all three biological replicates of the four strains and ranged from 1004 to 1082. In comparative analyses, 124, 135, and 134 proteins are differentially changed (over twofold) by overexpression of XgMT1, XgMT2, and XgMT3, respectively. These proteins are also categorized using cluster of orthologous group (COG) analyses, allowing postulation of biological mechanisms associated with three MTases in Xag. COGs reveal that the three MTases may play distinct roles, although some functions may overlap. These results are expected to allow new insight into understanding and predicting the biological functions of MTases in plant pathogenic bacteria. Data are available via ProteomeXchange (Identifier PXD012590)., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Background: Hfq is a widely conserved bacterial RNA-binding protein which generally mediates the global regulatory activities involv ed in physiological process and virulence. The goal of this study was to characterize the biological function of hfq gene in Xanthomonas axonpodis pv. citri (Xac), the causal agent of citrus canker disease., Results: An hfq mutant in Xac was generated by plasmid integration. The loss of hfq resulted in attenuation of bacterial growth, motility and biofilm formation. In addition, the hfq mutation impaired Xac resistance to H 2 O 2 and both high and low pH environments, but did not affect the virulence to citrus. RNA-Seq analyses indicated that Hfq played roles in regulating the expression of 746 genes. In hfq mutant, gene expression related to chemotaxis, secretion system, two-component system, quorum sensing and flagellar assembly were repressed, whereas expression of ribosomal genes were significantly up-regulated. The down-regulated expression of three bacterial chemotaxis related genes and seven flagella genes, which involved in cell growth and biofilm formation, were further validated by RT-qPCR., Conclusions: The study demonstrated that hfq was involved in multiple biological processes in Xac. The results could serve as initiate points for identifying regulatory sRNAs and genes controlled by Hfq-sRNA interactions in Xac.

Key Message: MeCIPK23 interacts with MeCBL1/9, and they confer improved defense response, providing potential genes for further genetic breeding in cassava. Cassava (Manihot esculenta) is an important food crop in tropical area, but its production is largely affected by cassava bacterial blight. However, the information of defense-related genes in cassava is very limited. Calcium ions play essential roles in plant development and stress signaling pathways. Calcineurin B-like proteins (CBLs) and CBL-interacting protein kinases (CIPKs) are crucial components of calcium signals. In this study, systematic expression profile of 25MeCIPKs in response to Xanthomonas axonopodis pv. manihotis (Xam) infection was examined, by which seven candidate MeCIPKs were chosen for functional investigation. Through transient expression in Nicotiana benthamiana leaves, we found that six MeCIPKs (MeCIPK5, MeCIPK8, MeCIPK12, MeCIPK22, MeCIPK23 and MeCIPK24) conferred improved defense response, via regulating the transcripts of several defense-related genes. Notably, we found that MeCIPK23 interacted with MeCBL1 and MeCBL9, and overexpression of these genes conferred improved defense response. On the contrary, virus-induced gene silencing of either MeCIPK23 or MeCBL1/9 or both genes resulted in disease sensitive in cassava. To our knowledge, this is the first study identifying MeCIPK23 as well as MeCBL1 and MeCBL9 that confer enhanced defense response against Xam.

Xanthomonas axonopodis pv. punicae (Xap) causing bacterial blight is an important pathogen that incurs significant losses to the exportability of pomegranate. Xap uses the Xop TTSS-effector, via the type three secretion system, to suppress pomegranate immunity. Here, we investigate the role of XopL during blight pathogenesis. We observed that XopL is essential for its in planta growth and full virulence. Leaves inoculated with Xap ΔxopL produced restricted water-soaked lesions compared to those inoculated with wild-type Xap. XopL supports Xap for its sustained multiplication in pomegranate by suppressing the plant cell death (PCD) event. We further demonstrated that XopL suppresses immune responses, such as callose deposition and production of reactive oxygen species (ROS). RT-qPCR analysis revealed that immune responsive genes were upregulated when challenged with Xap ΔxopL, whereas upregulation of such genes was compromised in the complemented strain containing the xopL gene. The transiently expressed XopL::EYFP fusion protein was localized to the plasma membrane, indicating the possible site of its action. Altogether, this study highlights that XopL is an important TTSS-effector of Xap that suppresses plant immune responses, including PCD, presumably to support the multiplication of Xap for a sufficient time-period during blight disease development., (© 2017 Institute of Botany, Chinese Academy of Sciences.)

Several studies have shown that mixtures of plant-growth-promoting rhizobacteria (PGPR) could enhance biological control activity for multiple plant diseases through the mechanisms of induced systemic resistance or antagonism. Prior experiments showed that four individual PGPR strains-AP69 (Bacillus altitudinis), AP197 (B. velezensis), AP199 (B. velezensis), and AP298 (B. velezensis)-had broad-spectrum biocontrol activity via antagonism in growth chambers against two foliar bacterial pathogens (Xanthomonas axonopodis pv. vesicatoria and Pseudomonas syringae pv. tomato) and one of two tested soilborne fungal pathogens (Rhizoctonia solani and Pythium ultimum). Based on these findings, the overall hypothesis of this study was that a mixture of two individual PGPR strains would exhibit better overall biocontrol and plant-growth promotion than the individual PGPR strains. Two separate greenhouse experiments were conducted. In each experiment, two individual PGPR strains and their mixtures were tested for biological control of three different diseases and for plant-growth promotion in the presence of the pathogens. The results demonstrated that the two individual PGPR strains and their mixtures exhibited both biological control of multiple plant diseases and plant-growth promotion. Overall, the levels of disease suppression and growth promotion were greater with mixtures than with individual PGPR strains.

This genetic diversity study aimed to estimate the population structure and explore the use of association mapping strategies to identify linked markers for bacterial resistance, growth and fruit quality in pomegranate collections from India. In total, 88 accessions including 37 cultivated types were investigated. A total of 112 alleles were amplified by use of 44 publicly available microsatellites for estimating molecular genetic diversity and population structure. Neighbor-joining analysis, model-based population structure and principal component analysis corroborated the genetic relationships among wild-type and cultivated pomegranate collections from India. Our study placed all 88 germplasm into four clusters. We identified a cultivated clade of pomegranates in close proximity to Daru types of wild-type pomegranates that grow naturally near the foothills of the Himalayas. Admixture analysis sorted various lineages of cultivated pomegranates to their respective ancestral forms. We identified four linked markers for fruit weight, titratable acidity and bacterial blight severity. PGCT001 was found associated with both fruit weight and bacterial blight, and the association with fruit weight during both seasons analyzed was significant after Bonferroni correction. This research demonstrates effectiveness of microsatellites to resolve population structure among the wild and cultivar collection of pomegranates and future use for association mapping studies.

Key Message: An RNAseq-based analysis of the cassava plants inoculated with Xam allowed the identification of transcriptional upregulation of genes involved in jasmonate metabolism, phenylpropanoid biosynthesis and putative targets for a TALE. Cassava bacterial blight, a disease caused by the gram-negative bacterium Xanthomonas axonopodis pv. manihotis (Xam), is a major limitation to cassava production worldwide and especially in developing countries. The molecular mechanisms underlying cassava susceptibility to Xam are currently unknown. To identify host genes and pathways leading to plant susceptibility, we analyzed the transcriptomic responses occurring in cassava plants challenged with either the non-pathogenic Xam strain ORST4, or strain ORST4(TALE1 Xam ) which is pathogenic due to the major virulence transcription activator like effector TALE1 Xam . Both strains triggered similar responses, i.e., induction of genes related to photosynthesis and phenylpropanoid biosynthesis, and repression of genes related to jasmonic acid signaling. Finally, to search for TALE1 Xam virulence targets, we scanned the list of cassava genes induced upon inoculation of ORST4(TALE1 Xam ) for candidates harboring a predicted TALE1 Xam effector binding element in their promoter. Among the six genes identified as potential candidate targets of TALE1 Xam a gene coding for a heat shock transcription factor stands out as the best candidate based on their induction in presence of TALE1 Xam and contain a sequence putatively recognized by TALE1 Xam .

Xanthomonas axonopodis pv. citri (Xac) is the causal agent of citrus bacterial canker (CBC) and is a serious problem worldwide. Like CBC, several important diseases in other fruits, such as mango, pomegranate, and grape, are also caused by Xanthomonas pathovars that display remarkable specificity toward their hosts. While citrus and mango diseases were documented more than 100 years ago, the pomegranate and grape diseases have been known only since the 1950s and 1970s, respectively. Interestingly, diseases caused by all these pathovars were noted first in India. Our genome-based phylogenetic studies suggest that these diverse pathogens belong to a single species and these pathovars may be just a group of rapidly evolving strains. Furthermore, the recently reported pathovars, such as those infecting grape and pomegranate, form independent clonal lineages, while the citrus and mango pathovars that have been known for a long time form one clonal lineage. Such an understanding of their phylogenomic relationship has further allowed us to understand major and unique variations in the lineages that give rise to these pathovars. Whole-genome sequencing studies including ecological relatives from their putative country of origin has allowed us to understand the evolutionary history of Xac and other pathovars that infect fruits., (Copyright © 2014, American Society for Microbiology. All Rights Reserved.)

Background: Xanthomonas axonopodis pv. citri (X. a. pv. citri) causes citrus canker that can result in defoliation and premature fruit drop with significant production losses worldwide. Biofilm formation is an important process in bacterial pathogens and several lines of evidence suggest that in X. a. pv. citri this process is a requirement to achieve maximal virulence since it has a major role in host interactions. In this study, proteomics was used to gain further insights into the functions of biofilms., Results: In order to identify differentially expressed proteins, a comparative proteomic study using 2D difference gel electrophoresis was carried out on X. a. pv. citri mature biofilm and planktonic cells. The biofilm proteome showed major variations in the composition of outer membrane proteins and receptor or transport proteins. Among them, several porins and TonB-dependent receptor were differentially regulated in the biofilm compared to the planktonic cells, indicating that these proteins may serve in maintaining specific membrane-associated functions including signaling and cellular homeostasis. In biofilms, UDP-glucose dehydrogenase with a major role in exopolysaccharide production and the non-fimbrial adhesin YapH involved in adherence were over-expressed, while a polynucleotide phosphorylase that was demonstrated to negatively control biofilm formation in E. coli was down-regulated. In addition, several proteins involved in protein synthesis, folding and stabilization were up-regulated in biofilms. Interestingly, some proteins related to energy production, such as ATP-synthase were down-regulated in biofilms. Moreover, a number of enzymes of the tricarboxylic acid cycle were differentially expressed. In addition, X. a. pv. citri biofilms also showed down-regulation of several antioxidant enzymes. The respective gene expression patterns of several identified proteins in both X. a. pv. citri mature biofilm and planktonic cells were evaluated by quantitative real-time PCR and shown to consistently correlate with those deduced from the proteomic study., Conclusions: Differentially expressed proteins are enriched in functional categories. Firstly, proteins that are down-regulated in X. a. pv. citri biofilms are enriched for the gene ontology (GO) terms 'generation of precursor metabolites and energy' and secondly, the biofilm proteome mainly changes in 'outer membrane and receptor or transport'. We argue that the differentially expressed proteins have a critical role in maintaining a functional external structure as well as enabling appropriate flow of nutrients and signals specific to the biofilm lifestyle.

Background and Aims: The use of vitamins including vitamin B1, B2 and K3 for the induction of systemic acquired resistance (SAR) to protect crops against plant pathogens has been evaluated previously. The use of vitamins is beneficial because it is cost effective and safe for the environment. The use of folate precursors, including ortho-aminobenzoic acid, to induce SAR against a soft-rot pathogen in tobacco has been reported previously., Methods: In the present study, para-aminobenzoic acid (PABA, also referred to as vitamin Bx) was selected owing to its effect on the induction of SAR against Xanthomonas axonopodis pv. vesicatoria in pepper plants through greenhouse screening., Key Results: Dipping of pepper seedlings in a 1 mm PABA solution in field trials induced SAR against artificially infiltrated X. axonopodis pv. vesicatoria and naturally occurring cucumber mosaic virus. Expression of the Capsicum annuum pathogenesis-related 4 gene was primed in response to pathogen infection as assessed by quantitative real-time PCR. The accumulation of cucumber mosaic virus RNA was reduced in PABA-treated pepper plants at 40 and 105 d post-treatment. Unexpectedly, fruit yield was increased in PABA-treated plants, indicating that PABA-mediated SAR successfully protected pepper plants from infection by bacterial and viral pathogens without significant fitness allocation costs., Conclusions: The present study is the first to demonstrate the effective elicitation of SAR by a folate precursor under field conditions.

Citrus bacterial canker caused by Xanthomonas axonopodis pv. citri is a serious disease that impacts citrus production worldwide, and X. axonopodis pv. citri is listed as a quarantine pest in certain countries. Biofilm formation is important for the successful development of a pathogenic relationship between various bacteria and their host(s). To understand the mechanisms of biofilm formation by X. axonopodis pv. citri strain XW19, the strain was subjected to transposon mutagenesis. One mutant with a mutation in a two-component response regulator gene that was deficient in biofilm formation on a polystyrene microplate was selected for further study. The protein was designated as BfdR for biofilm formation defective regulator. BfdR from strain XW19 shares 100% amino acid sequence identity with XAC1284 of X. axonopodis pv. citri strain 306 and 30-100% identity with two-component response regulators in various pathogens and environmental microorganisms. The bfdR mutant strain exhibited significantly decreased biofilm formation on the leaf surfaces of Mexican lime compared with the wild type strain. The bfdR mutant was also compromised in its ability to cause canker lesions. The wild-type phenotype was restored by providing pbfdR in trans in the bfdR mutant. Our data indicated that BfdR did not regulate the production of virulence-related extracellular enzymes including amylase, lipase, protease, and lecithinase or the expression of hrpG, rfbC, and katE; however, BfdR controlled the expression of rpfF in XVM2 medium, which mimics cytoplasmic fluids in planta. In conclusion, biofilm formation on leaf surfaces of citrus is important for canker development in X. axonopodis pv. citri XW19. The process is controlled by the two-component response regulator BfdR via regulation of rpfF, which is required for the biosynthesis of a diffusible signal factor.

Type IV pili (T4P) are polar surface structures that play important roles in bacterial motility, biofilm formation, and pathogenicity. The protein FimX and its orthologs are known to mediate T4P formation in the human pathogen Pseudomonas aeruginosa and some other bacterial species. It was reported recently that FimX(XAC2398) from Xanthomonas axonopodis pv. citri interacts with PilZ(XAC1133) directly through the nonenzymatic EAL domain of FimX(XAC2398). Here we present experimental data to reveal that the strong interaction between FimX(XAC2398) and PilZ(XAC1133) is not conserved in P. aeruginosa and likely other Pseudomonas species. In vitro and in vivo binding experiments showed that the interaction between FimX and PilZ in P. aeruginosa is below the measurable limit. Surface plasmon resonance assays further confirmed that the interaction between the P. aeruginosa proteins is at least more than 3 orders of magnitude weaker than that between the X. axonopodis pv. citri pair. The N-terminal lobe region of FimX(XAC2398) was identified as the binding surface for PilZ(XAC1133) by amide hydrogen-deuterium exchange and site-directed mutagenesis studies. Lack of several key residues in the N-terminal lobe region of the EAL domain of FimX is likely to account for the greatly reduced binding affinity between FimX and PilZ in P. aeruginosa. All together, the results suggest that the interaction between PilZ and FimX in Xanthomonas species is not conserved in P. aeruginosa due to the evolutionary divergence among the FimX orthologs. The precise roles of FimX and PilZ in bacterial motility and T4P biogenesis are likely to vary among bacterial species.

Common bacterial blight (CBB), caused by Xanthomonas axonopodis pv. phaseoli (Xap), is a major yield-limiting factor of common bean (Phaseolus vulgaris L.) production around the world. Two major CBB-resistant quantitative trait loci (QTL), linked to the sequence characterized amplified region markers BC420 and SU91, are located at chromosomes 6 and 8, respectively. Using map-based cloning approach, four bacterial artificial chromosome (BAC) clones from the BC420-QTL locus and one BAC clone containing SU91 were sequenced by Roche 454 technique and subsequently assembled using merged assemblies from three different programs. Based on the quality of the assembly, only the sequences of BAC 32H6 and 4K7 were used for candidate gene marker (CGM) development and candidate gene (CG) selection. For the BC420-QTL locus, 21 novel genes were predicted in silico by FGENESH using Medicago gene model, whereas 16 genes were identified in the SU91-QTL locus. For each putative gene, one or more primer pairs were designed and tested in the contrasting near isogenic lines. Overall, six and nine polymorphic markers were found in the SU91- and BC420-QTL loci, respectively. Afterwards, association mapping was conducted in a breeding population of 395 dry bean lines to discover marker-trait associations. Two CGMs per each locus showed better association with CBB resistance than the BC420 and SU91 markers, which include BC420-CG10B and BC420-CG14 for BC420_QTL locus, and SU91-CG10 and SU91-CG11 for SU91_QTL locus. The strong associations between CBB resistance and the CGs 10 and 14 from BC420_QTL locus and the CGs 10 and 11 from SU91_QTL locus indicate that the genes 10 and 14 from the BC420 locus are potential CGs underlying the BC420_QTL locus, whereas the genes 10 and 11 from the SU91 locus are potential CGs underlying the SU91_QTL locus. The superiority of SU91-CG11 was further validated in a recombinant inbred line population Sanilac × OAC 09-3. Thus, co-dominant CGMs, BC420-CG14 and SU91-CG11, are recommended to replace BC420 and SU91 for marker-assisted selection of common bean with resistance to CBB.

Recent studies have demonstrated that an appropriate light environment is required for the establishment of efficient vegetal resistance responses in several plant-pathogen interactions. The photoreceptors implicated in such responses are mainly those belonging to the phytochrome family. Data obtained from bacterial genome sequences revealed the presence of photosensory proteins of the BLUF (Blue Light sensing Using FAD), LOV (Light, Oxygen, Voltage) and phytochrome families with no known functions. Xanthomonas axonopodis pv. citri is a Gram-negative bacterium responsible for citrus canker. The in silico analysis of the X. axonopodis pv. citri genome sequence revealed the presence of a gene encoding a putative LOV photoreceptor, in addition to two genes encoding BLUF proteins. This suggests that blue light sensing could play a role in X. axonopodis pv. citri physiology. We obtained the recombinant Xac-LOV protein by expression in Escherichia coli and performed a spectroscopic analysis of the purified protein, which demonstrated that it has a canonical LOV photochemistry. We also constructed a mutant strain of X. axonopodis pv. citri lacking the LOV protein and found that the loss of this protein altered bacterial motility, exopolysaccharide production and biofilm formation. Moreover, we observed that the adhesion of the mutant strain to abiotic and biotic surfaces was significantly diminished compared to the wild-type. Finally, inoculation of orange (Citrus sinensis) leaves with the mutant strain of X. axonopodis pv. citri resulted in marked differences in the development of symptoms in plant tissues relative to the wild-type, suggesting a role for the Xac-LOV protein in the pathogenic process. Altogether, these results suggest the novel involvement of a photosensory system in the regulation of physiological attributes of a phytopathogenic bacterium. A functional blue light receptor in Xanthomonas spp. has been described for the first time, showing an important role in virulence during citrus canker disease.

Citrus bacterial canker caused by Xanthomonas axonopodis pv. citri is a devastating disease resulting in significant crop losses in various citrus cultivars worldwide. A biocontrol agent has not been recommended for this disease. To explore the potential of bacilli native to Taiwan to control this disease, Bacillus species with a broad spectrum of antagonistic activity against various phytopathogens were isolated from plant potting mixes, organic compost and the rhizosphere soil. Seven strains TKS1-1, OF3-16, SP4-17, HSP1, WG6-14, TLB7-7, and WP8-12 showing superior antagonistic activity were chosen for biopesticide development. The genetic identity based on 16S rDNA sequences indicated that all seven native strains were close relatives of the B. subtilis group and appeared to be discrete from the B. cereus group. DNA polymorphisms in strains WG6-14, SP4-17, TKS1-1, and WP8-12, as revealed by repetitive sequence-based PCR with the BOXA1R primers were similar to each other, but different from those of the respective Bacillus type strains. However, molecular typing of the strains using either tDNA-intergenic spacer regions or 16S-23S intergenic transcribed spacer regions was unable to differentiate the strains at the species level. Strains TKS1-1 and WG6-14 attenuated symptom development of citrus bacterial canker, which was found to be correlated with a reduction in colonization and biofilm formation by X. axonopodis pv. citri on leaf surfaces. The application of a Bacillus strain TKS1-1 endospore formulation to the leaf surfaces of citrus reduced the incidence of citrus bacterial canker and could prevent development of the disease.

Xanthomonas axonopodis pv. citrumelo is a citrus pathogen causing citrus bacterial spot disease that is geographically restricted within the state of Florida. Illumina, 454 sequencing, and optical mapping were used to obtain a complete genome sequence of X. axonopodis pv. citrumelo strain F1, 4.9 Mb in size. The strain lacks plasmids, in contrast to other citrus Xanthomonas pathogens. Phylogenetic analysis revealed that this pathogen is very close to the tomato bacterial spot pathogen X. campestris pv. vesicatoria 85-10, with a completely different host range. We also compared X. axonopodis pv. citrumelo to the genome of citrus canker pathogen X. axonopodis pv. citri 306. Comparative genomic analysis showed differences in several gene clusters, like those for type III effectors, the type IV secretion system, lipopolysaccharide synthesis, and others. In addition to pthA, effectors such as xopE3, xopAI, and hrpW were absent from X. axonopodis pv. citrumelo while present in X. axonopodis pv. citri. These effectors might be responsible for survival and the low virulence of this pathogen on citrus compared to that of X. axonopodis pv. citri. We also identified unique effectors in X. axonopodis pv. citrumelo that may be related to the different host range as compared to that of X. axonopodis pv. citri. X. axonopodis pv. citrumelo also lacks various genes, such as syrE1, syrE2, and RTX toxin family genes, which were present in X. axonopodis pv. citri. These may be associated with the distinct virulences of X. axonopodis pv. citrumelo and X. axonopodis pv. citri. Comparison of the complete genome sequence of X. axonopodis pv. citrumelo to those of X. axonopodis pv. citri and X. campestris pv. vesicatoria provides valuable insights into the mechanism of bacterial virulence and host specificity.

Xanthomonas axonopodis pv. citri (Xac) causes citrus canker, provoking defoliation and premature fruit drop with concomitant economical damage. In plant pathogenic bacteria, lipopolysaccharides are important virulence factors, and they are being increasingly recognized as major pathogen-associated molecular patterns for plants. In general, three domains are recognized in a lipopolysaccharide: the hydrophobic lipid A, the hydrophilic O-antigen polysaccharide, and the core oligosaccharide, connecting lipid A and O-antigen. In this work, we have determined the structure of purified lipopolysaccharides obtained from Xanthomonas axonopodis pv. citri wild type and a mutant of the O-antigen ABC transporter encoded by the wzt gene. High pH anion exchange chromatography and matrix-assisted laser desorption/ionization mass spectrum analysis were performed, enabling determination of the structure not only of the released oligosaccharides and lipid A moieties but also the intact lipopolysaccharides. The results demonstrate that Xac wild type and Xacwzt LPSs are composed mainly of a penta- or tetra-acylated diglucosamine backbone attached to either two pyrophosphorylethanolamine groups or to one pyrophosphorylethanolamine group and one phosphorylethanolamine group. The core region consists of a branched oligosaccharide formed by Kdo₂Hex₆GalA₃Fuc3NAcRha₄ and two phosphate groups. As expected, the presence of a rhamnose homo-oligosaccharide as O-antigen was determined only in the Xac wild type lipopolysaccharide. In addition, we have examined how lipopolysaccharides from Xac function in the pathogenesis process. We analyzed the response of the different lipopolysaccharides during the stomata aperture closure cycle, the callose deposition, the expression of defense-related genes, and reactive oxygen species production in citrus leaves, suggesting a functional role of the O-antigen from Xac lipopolysaccharides in the basal response.

Background: Enormous work has shown that polyamines are involved in a variety of physiological processes, but information is scarce on the potential of modifying disease response through genetic transformation of a polyamine biosynthetic gene., Results: In the present work, an apple spermidine synthase gene (MdSPDS1) was introduced into sweet orange (Citrus sinensis Osbeck 'Anliucheng') via Agrobacterium-mediated transformation of embryogenic calluses. Two transgenic lines (TG4 and TG9) varied in the transgene expression and cellular endogenous polyamine contents. Pinprick inoculation demonstrated that the transgenic lines were less susceptible to Xanthomonas axonopodis pv. citri (Xac), the causal agent of citrus canker, than the wild type plants (WT). In addition, our data showed that upon Xac attack TG9 had significantly higher free spermine (Spm) and polyamine oxidase (PAO) activity when compared with the WT, concurrent with an apparent hypersensitive response and the accumulation of more H₂O₂. Pretreatment of TG9 leaves with guazatine acetate, an inhibitor of PAO, repressed PAO activity and reduced H₂O₂ accumulation, leading to more conspicuous disease symptoms than the controls when both were challenged with Xac. Moreover, mRNA levels of most of the defense-related genes involved in synthesis of pathogenesis-related protein and jasmonic acid were upregulated in TG9 than in the WT regardless of Xac infection., Conclusion: Our results demonstrated that overexpression of the MdSPDS1 gene prominently lowered the sensitivity of the transgenic plants to canker. This may be, at least partially, correlated with the generation of more H₂O₂ due to increased production of polyamines and enhanced PAO-mediated catabolism, triggering hypersensitive response or activation of defense-related genes.

Background: Common bacterial blight (CBB), incited by Xanthomonas axonopodis pv. phaseoli (Xap), is a major yield-limiting factor of common bean (Phaseolus vulgaris L.) production around the world. Host resistance is practically the most effective and environmentally-sound approach to control CBB. Unlike conventional QTL discovery strategies, in which bi-parental populations (F2, RIL, or DH) need to be developed, association mapping-based strategies can use plant breeding populations to synchronize QTL discovery and cultivar development., Results: A population of 469 dry bean lines of different market classes representing plant materials routinely developed in a bean breeding program were used. Of them, 395 lines were evaluated for CBB resistance at 14 and 21 DAI (Days After Inoculation) in the summer of 2009 in an artificially inoculated CBB nursery in south-western Ontario. All lines were genotyped using 132 SNPs (Single Nucleotide Polymorphisms) evenly distributed across the genome. Of the 132 SNPs, 26 SNPs had more than 20% missing data, 12 SNPs were monomorphic, and 17 SNPs had a MAF (Minor Allelic Frequency) of less than 0.20, therefore only 75 SNPs were used for association study, based on one SNP per locus. The best possible population structure was to assign 36% and 64% of the lines into Andean and Mesoamerican subgroups, respectively. Kinship analysis also revealed complex familial relationships among all lines, which corresponds with the known pedigree history. MLM (Mixed Linear Model) analysis, including population structure and kinship, was used to discover marker-trait associations. Eighteen and 22 markers were significantly associated with CBB rating at 14 and 21 DAI, respectively. Fourteen markers were significant for both dates and the markers UBC420, SU91, g321, g471, and g796 were highly significant (p ≤ 0.001). Furthermore, 12 significant SNP markers were co-localized with or close to the CBB-QTLs identified previously in bi-parental QTL mapping studies., Conclusions: This study demonstrated that association mapping using a reasonable number of markers, distributed across the genome and with application of plant materials that are routinely developed in a plant breeding program can detect significant QTLs for traits of interest.

Xanthomonas axonopodis pv. citri (Xac) is the causative agent of citrus canker. This bacterium develops a characteristic biofilm on both biotic and abiotic surfaces. To evaluate the participation of the single flagellum of Xac in biofilm formation, mutants in the fliC (flagellin) and the flgE (hook) genes were generated. Swimming motility, assessed on 0.25 % agar plates, was markedly reduced in fliC and flgE mutants. However, the fliC and flgE mutants exhibited a flagellar-independent surface translocation on 0.5 % agar plates. Mutation of either the rpfF or the rpfC gene, which both encode proteins involved in cell-cell signalling mediated by diffusible signal factor (DSF), led to a reduction in both flagellar-dependent and flagellar-independent surface translocation, indicating a regulatory role for DSF in both types of motility. Confocal laser scanning microscopy of biofilms produced in static culture demonstrated that the flagellum is also involved in the formation of mushroom-shaped structures and water channels, and in the dispersion of biofilms. The presence of the flagellum was required for mature biofilm development on lemon leaf surfaces. The absence of flagellin produced a slight reduction in Xac pathogenicity and this reduction was more severe when the complete flagellum structure was absent.

Common bacterial blight (CBB), incited by Xanthomonas axonopodis pv. phaseoli (Xap), is a serious seed-borne disease of common bean (Phaseolus vulgaris L.) in both temperate and tropical production zones. The line HR45 is highly resistant to Xap infection on leaves and pods in both field and greenhouse. To understand the molecular mechanisms underlying CBB resistance in HR45, cDNA-amplified fragment length polymorphism (AFLP) technique was used to identify the genes that are differentially expressed in the leaves of HR45 at different time-periods after inoculation. Selective amplifications with 34 primer combinations allowed the visualization of 2,448 transcript-derived fragments (TDFs) in infected leaves, and 259 (10.6%) of them were differentially expressed TDFs (DE-TDFs). Seventy-seven of the DE-TDFs were cloned and sequenced. Thirty-nine of the 77 (50.6%) DE-TDFs representing bean transcripts were not previously reported in any EST database. The expression patterns of 10 representative DE-TDFs were further confirmed by real-time RT-PCR. BLAST analysis suggested that 40% (31 of 77) of the DE-TDFs were homologous to the genes related to metabolism, photosynthesis, and cellular transport, whereas 28% (22 of 77) of the DE-TDFs showed homology to the genes involved in defence response, response to stimulus, enzyme regulation, and transcription regulation. Thus, the 22 pathogenesis-related DE-TDFs were selected as potential functional candidate genes (FCGs) in association with CBB resistance. Meanwhile, six of the DE-TDFs (1FCG and five other DE-TDFs) were in silico mapped to the distal region of the bean linkage group B6 (the genomic location containing the major CBB resistance QTL in HR45) and, therefore, were considered as positional candidate genes (PCGs). This study represents a first step towards the discovery of bean genes expressed upon Xap infection. This information will be useful for elucidating the molecular basis of the resistance response process and identifying the genes that underlie the CBB-resistance.

Xanthomonas axonopodis pv. citri (Xac) causes citrus canker disease, a major threat to citrus production worldwide. Accumulating evidence suggests that the formation of biofilms on citrus leaves plays an important role in the epiphytic survival of this pathogen prior to the development of canker disease. However, the process of Xac biofilm formation is poorly understood. Here, we report a genome-scale study of Xac biofilm formation in which we identified 92 genes, including 33 novel genes involved in biofilm formation and 7 previously characterized genes, colR, fhaB, fliC, galU, gumD, wxacO, and rbfC, known to be important for Xac biofilm formation. In addition, 52 other genes with defined or putative functions in biofilm formation were identified, even though they had not previously reported been to be associated with biofilm formation. The 92 genes were isolated from 292 biofilm-defective mutants following a screen of a transposon insertion library containing 22,000 Xac strain 306 mutants. Further analyses indicated that 16 of the novel genes are involved in the production of extracellular polysaccharide (EPS) and/or lipopolysaccharide (LPS), 7 genes are involved in signaling and regulatory pathways, and 5 genes have unknown roles in biofilm formation. Furthermore, two novel genes, XAC0482, encoding a haloacid dehalogenase-like phosphatase, and XAC0494 (designated as rbfS), encoding a two-component sensor protein, were confirmed to be biofilm-related genes through complementation assays. Our data demonstrate that the formation of mature biofilm requires EPS, LPS, both flagellum-dependent and flagellum-independent cell motility, secreted proteins and extracellular DNA. Additionally, multiple signaling pathways are involved in Xac biofilm formation. This work is the first report on a genome-wide scale of the genetic processes of biofilm formation in plant pathogenic bacteria. The report provides significant new information about the genetic determinants and regulatory mechanism of biofilm formation.

The natural resistance of plants to disease is based not only on preformed mechanisms, but also on induced mechanisms. The defense mechanisms present in resistant plants may also be found in susceptible ones. This study attempted to analyze the metabolic alterations in plants of the potato Solanum tuberosum L. cv. Agata that were inoculated with the incompatible plant-pathogenic bacteria X. axonopodis and R. solanacearum, and the compatible bacterium E. carotovora. Levels of total phenolic compounds, including the flavonoid group, and the activities of polyphenol oxidase (PPO) and peroxidase (POX) were evaluated. Bacteria compatibility was evaluated by means of infiltration of tubers. The defense response was evaluated in the leaves of the potato plants. Leaves were inoculated depending on their number and location on the stem. Multiple-leaf inoculation was carried out on basal, intermediate, and apical leaves, and single inoculations on intermediate leaves. Leaves inoculated with X. axonopodis and with R. solanacearum showed hypersensitive responses within 24 hours post-inoculation, whereas leaves inoculated with E. carotovora showed disease symptoms. Therefore, the R. solanacearum isolate used in the experiments did not exhibit virulence to this potato cultivar. Regardless of the bacterial treatments, the basal leaves showed higher PPO and POX activities and lower levels of total phenolic compounds and flavonoids, compared to the apical leaves. However, basal and intermediate leaves inoculated with R. solanacearum and X. axonopodis showed increases in total phenolic compounds and flavonoid levels. In general, multiple-leaf inoculation showed the highest levels of total phenolics and flavonoids, whereas the single inoculations resulted in the highest increase in PPO activity. The POX activity showed no significant difference between single- and multiple-leaf inoculations. Plants inoculated with E. carotovora showed no significant increase in defense mechanisms such as enzyme activity and phenolic compounds. Therefore, resistance or susceptibility in S. tuberosum cv. Agata might depend on leaf age, type of inoculation performed (single or multiple), and the interaction between plant and pathogen.

Xanthomonas axonopodis pv. citri (Xac) and Xanthomonas axonopodis pv. aurantifolii pathotype C (Xaa) are responsible for citrus canker disease; however, while Xac causes canker on all citrus varieties, Xaa is restricted to Mexican lime, and in sweet oranges it triggers a defence response. To gain insights into the differential pathogenicity exhibited by Xac and Xaa and to survey the early molecular events leading to canker development, a detailed transcriptional analysis of sweet orange plants infected with the pathogens was performed. Using differential display, suppressed subtractive hybridization and microarrays, we identified changes in transcript levels in approximately 2.0% of the approximately 32,000 citrus genes examined. Genes with altered expression in response to Xac/Xaa surveyed at 6 and 48 h post-infection (hpi) were associated with cell-wall modifications, cell division and expansion, vesicle trafficking, disease resistance, carbon and nitrogen metabolism, and responses to hormones auxin, gibberellin and ethylene. Most of the genes that were commonly modulated by Xac and Xaa were associated with basal defences triggered by pathogen-associated molecular patterns, including those involved in reactive oxygen species production and lignification. Significantly, we detected clear changes in the transcriptional profiles of defence, cell-wall, vesicle trafficking and cell growth-related genes in Xac-infected leaves between 6 and 48 hpi. This is consistent with the notion that Xac suppresses host defences early during infection and simultaneously changes the physiological status of the host cells, reprogramming them for division and growth. Notably, brefeldin A, an inhibitor of vesicle trafficking, retarded canker development. In contrast, Xaa triggered a mitogen-activated protein kinase signalling pathway involving WRKY and ethylene-responsive transcriptional factors known to activate downstream defence genes.

Based on the number of new reports during the last two decades, bacterial blight of onion (Allium cepa) is considered an emerging disease. The causal agent, Xanthomonas axonopodis pv. allii, is pathogenic to several Allium species after inoculation, but outbreaks worldwide have been primarily reported on onion. We describe a unique epidemiological situation in Réunion Island, France, with concomitant outbreaks on three Allium species, onion, leek (A. porrum), and garlic (A. sativum). There was no host specialization within Allium spp. among strains associated with the three host species. Based on amplified fragment length polymorphism (AFLP) and restriction fragment length polymorphism, strains associated with these outbreaks in Réunion Island were highly related genetically to strains isolated from diseased plant samples and contaminated seed lots in the neighboring island of Mauritius, where the disease has occurred since 1984. All AFLP haplotypes were identified as X. axonopodis pv. allii based on polymerase chain reaction analysis using specific primers, biochemical tests, and/or pathogenicity tests. Two genetically related groups of strains (A and B) that can be distinguished by AFLP, differential utilization of three carbon sources, and xanthomonadin pigment production were detected initially after establishment of the pathogen. In less than 10 years after the establishment of the pathogen there was nearly an extinction of group A strains in Réunion Island, suggesting differences in fitness between strains in the two groups.

The full-length cDNA of CaAbsi1 encodes a presumptive protein of 134 amino acid residues that has homology to a putative zinc finger protein in its C-terminus. The deduced amino acid sequence has 50% homology to Oryza sativa NP001049-274, the function of which is unknown. Expression of CaAbsi1 was reduced in response to inoculation of non-host pathogens. On the other hand it was induced one hour after exposure to high concentrations of NaCl or mannitol, and six hours after transfer to low temperature. Induction also occurred in response to oxidative stress, methyl viologen, hydrogen peroxide and abscisic acid. Our results suggest that CaAbsi1 plays a role in multiple responses to wounding and abiotic stresses.

The phytopathogenic bacterium Xanthomonas axonopodis pv. citri is responsible for the canker disease affecting citrus plants throughout the world. Here, we have evaluated the role of bacterial attachment and biofilm formation in leaf colonization during canker development on lemon leaves. Crystal violet staining and confocal laser scanning microscopy analysis of X. axonopodis pv. citri strains expressing the green fluorescent protein were used to evaluate attachment and biofilm formation on abiotic and biotic (leaf) surfaces. Wild-type X. axonopodis pv. citri attached to and formed a complex, structured biofilm on glass in minimal medium containing glucose. Similar attachment and structured biofilm formation also were seen on lemon leaves. An X. axonopodis pv. citri gumB mutant strain, defective in production of the extracellular polysaccharide xanthan, did not form a structured biofilm on either abiotic or biotic surfaces. In addition, the X. axonopodis pv. citri gumB showed reduced growth and survival on leaf surfaces and reduced disease symptoms. These findings suggest an important role for formation of biofilms in the epiphytic survival of X. axonopodis pv. citri prior to development of canker disease.

The CCR4-associated factor 1 (CAF1) protein belongs to the CCR4-NOT complex, which is an evolutionary conserved protein complex and plays an important role in the control of transcription and mRNA decay in yeast and mammals. To investigate the function of CAF1 in plants, we performed gain- and loss-of-function studies by overexpression of the pepper CAF1 (CaCAF1) in tomato and virus-induced gene silencing (VIGS) of the gene in pepper plants. Overexpression of CaCAF1 in tomato resulted in significant growth enhancement, with increasing leaf thickness, and enlarged cell size by more than twofold when compared with the control plants. A transmission electron microscopic analysis revealed that the CaCAF1-transgenic tomato plants had thicker cell walls and cuticle layers than the control plants. In addition to developmental changes, overexpression of CaCAF1 in tomato plants resulted in enhanced resistance against the oomycete pathogen Phytophthora infestans. Additionally, microarray, northern and real-time polymerase chain reaction analyses of CaCAF1-transgenic tomato plants revealed that multiple genes were constitutively upregulated, including genes involved in polyamine biosynthesis, defence reactions and cell-wall organogenesis. In contrast, VIGS of CaCAF1 in pepper plants caused significant growth retardation and enhanced susceptibility to the pepper bacterial spot pathogen Xanthomonas axonopodis pv. vesicatoria. Our results suggest roles for plant CAF1 in normal growth and development, as well as in defence against pathogens.

Genome annotation of the plant pathogen Xanthomonas axonopodis pv. citri (Xac), identified flagellar genes in a 15.7 kb gene cluster. However, FlgN, a secretion chaperone for hook-associated proteins FlgK and FlgL, was not identified. We performed extensive screening of the X. axonopodis pv. citri genome with the yeast two-hybrid system to identify a protein with the characteristics of the flagellar chaperone FlgN. We found a candidate (XAC1990) encoded by an operon for components of the flagellum apparatus that interacted with FlgK. In order to further support this finding, Xac FlgK and XAC1990 were cloned, expressed, and purified. The recombinant proteins were characterized by spectroscopic methods and their interaction in vitro confirmed by pull-down assays. We, therefore, conclude that XAC1990 and its homologs in other Xanthomonas species are, in fact, FlgN proteins. These observations extend the sequence diversity covered by this family of proteins.

Xanthan-deficient mutants of Xanthomonas axonopodis pv. citri, the bacterium responsible for citrus canker, were generated by deletion and marker exchange of the region encoding the carboxy-terminal end of the first glycosyltransferase, GumD. Mutants of gumD did not produce xanthan and remained pathogenic in citrus plants to the same extent as wild-type bacteria. The kinetics of appearance of initial symptoms, areas of plant material affected, and growth of bacteria inside plant tissue throughout the disease process were similar for both wild-type and mutant inoculations. Moreover, exopolysaccharide deficiency did not impair the ability of the bacteria to induce hypersensitive response on non-host plants. Apart from variations in phenotypic aspects, no differences in growth or survival under different stress conditions were observed between the xanthan-deficient mutant and wild-type bacteria. However, gumD mutants displayed impaired survival under oxidative stress during stationary phase as well as impaired epiphytic survival on citrus leaves. Our results suggest that xanthan does not play an essential role in citrus canker at the initial stages of infection or in the incompatible interactions between X. axonopodis pv. citri and non-host plants, but facilitates the maintenance of bacteria on the host plant, possibly improving the efficiency of colonization of distant tissue.

Citrus bacterial canker is an important disease of Citrus species in China. The disease severely occurs especially in the coastal area. Integrated control system has been used for the control of the disease, in which chemotherapy plays an important role at present. The chemotherapy-dominant control system brought many problems to the environment, such as chemical residua in the products and induction of resistance to fungicide(s) by the pathogen. To solve these problems, an intensive study on biocontrol of citrus bacterial canker is needed. Isolations and characterizations of biocontrol agents are the basis for biocontrol of the disease. A bacterial strain Bt8 with strong inhibiting ability against Xanthomonas axonopodis pv. citri (Hasse) Vauterin, was isolated from citrus orchard soil in Nanning, China. The isolated bacterial strain was identified and characterized as Acinetobacter baumannii Bouvet et Grimont on the base of its morphology and 16S rDNA sequence analysis as well as physiological and biochemical characters. The inhibiting activity of the bacterium suspension against the pathogen was significantly influenced by environmental factors, such as temperatures, pHs and media. At temperatures of 18 degrees C to 33 degrees C, both the inhibiting activity of the bacterium suspension and the biomass of the bacterium increased with the increases of temperatures, suggesting that the influence of temperature on inhibiting activity of the bacterium suspension was in dependence on the bacterial biomass. In NA liquid medium of pH 10, the bacterium suspension showed the highest inhibiting activity against Xanthomonas axonopodis pv. citri, which was not in dependence on biomass of the bacterium. The bacterium suspension provided 55.2% inhibition against bacterial canker under greenhouse conditions. The results showed that Acinetobacter baumannii has potential as biocontrol agent against bacterial canker disease. Acinetobacter baumannii was reported as the pathogens infecting human and animals. The present study enriched the understanding on biological diversity in Acinetobacter baumannii to sciences. This is the first report on the isolation of Acinetobacter baumannii with strong inhibiting ability against plant pathogen.

Large-scale single-pass sequencing of cDNA libraries and microarray analysis have proven to be useful tools for discovering new genes and studying gene expression. As a first step in elucidating the defense mechanisms in hot pepper plants, a total of 8,525 expressed sequence tags (ESTs) were generated and analyzed in silico. The cDNA microarray analysis identified 613 hot pepper genes that were transcriptionally responsive to the non-host soybean pustule pathogen Xanthomonas axonopodis pv. glycines ( Xag). Several functional types of genes, including those involved in cell wall modification/biosynthesis, transport, signaling pathways and divergent defense reactions, were induced at the early stage of Xag infiltration. In contrast, genes encoding proteins that are involved in photosynthesis, carbohydrate metabolism and the synthesis of chloroplast biogenetic proteins were down-regulated at the late stage of Xag infiltration. These expression profiles share common features with the expression profiles elicited by other stresses, such as fungal challenge, wounding, cold, drought and high salinity. However, we also identified several novel transcription factors that may be specifically involved in the defense reaction of the hot pepper. We also found that the defense reaction of the hot pepper may involve the deactivation of gibberellin. Furthermore, many genes encoding proteins with unknown function were identified. Functional analysis of these genes may broaden our understanding of non-host resistance. This study is the first report of large-scale sequencing and non-host defense transcriptome analysis of the hot pepper plant species. (The sequence data in this paper have been submitted to the dbEST and GenBank database under the codes 10227604-10236595 and BM059564-BM068555, respectively. Additional information is available at http://plant.pdrc.re.kr/ks200201/pepper.html).