XA21-mediated resistance to Xanthomonas oryzae pv. oryzae is dose dependent.

The rice receptor kinase XA21 confers broad-spectrum resistance to Xanthomonas oryzae pv. oryzae (Xoo), the causal agent of rice bacterial blight disease. To investigate the relationship between the expression level of XA21 and resulting resistance, we generated independent HA-XA21 transgenic rice lines accumulating the XA21 immune receptor fused with an HA epitope tag. Whole-genome sequence analysis identified the T-DNA insertion sites in sixteen independent T0 events. Through quantification of the HA-XA21 protein and assessment of the resistance to Xoo strain PXO99 in six independent transgenic lines, we observed that XA21-mediated resistance is dose dependent. In contrast, based on the four agronomic traits quantified in these experiments, yield is unlikely to be affected by the expression level of HA-XA21. These findings extend our knowledge of XA21-mediated defense and contribute to the growing number of well-defined genomic landing pads in the rice genome that can be targeted for gene insertion without compromising yield.

Understanding the nature of blast resistance in combined bacterial leaf blight and blast gene pyramided lines of rice variety tellahamsa.

BACKGROUND: Rice blast and bacterial leaf blight (BLB) are the most limiting factors for rice production in the world which cause yield losses typically ranging from 20 to 30% and can be as high as 50% in some areas of Asia especially India under severe infection conditions. METHODS AND RESULTS: An improved line of Tellahamsa, TH-625-491 having two BLB resistance genes (xa13 and Xa21) and two blast resistance genes (Pi54 and Pi1) with 95% Tellahamsa genome was used in the present study. TH-625-491 was validated for all four target genes and was used for backcrossing with Tellahamsa. Seventeen IBC1F1 plants heterozygous for all four target genes, 19 IBC1F2 plants homozygous for four, three and two gene combinations and 19 IBC1F2:3 plants also homozygous for four, three and two gene combinations were observed. Among seventeen IBC1F1 plants, IBC1F1-62 plant recorded highest recurrent parent genome (97.5%) covering 75 polymorphic markers. Out of the total of 920 IBC1F2 plants screened, 19 homozygous plants were homozygous for four, three and two target genes along with bacterial blight resistance. Background analysis was done in all 19 homozygous IBC1F2 plants possessing BLB resistance (possessing xa13, Xa21, Pi54 and Pi1 in different combinations) with five parental polymorphic SSR markers. IBC1F2-62-515 recovered 98.5% recurrent parent genome. The four, three and two gene pyramided lines of Tellahamsa exhibited varying resistance to blast. CONCLUSIONS: Results show that there might be presence of antagonistic effect between bacterial blight and blast resistance genes since the lines with Pi54 and Pi1 combination are showing better resistance than the combinations with both bacterial blight and blast resistance genes.

Precision mapping and expression analysis of recessive bacterial blight resistance gene xa-45(t) from Oryza glaberrima.

BACKGROUND: Bacterial blight, caused by Xanthomonas oryzae pv. oryzae (Xoo), is one of the most devastating diseases of rice leading to huge yield losses in Southeast Asia. The recessive resistance gene xa-45(t) from Oryza glaberrima IRGC102600B, mapped on rice chromosome 8, spans 80 Kb with 9 candidate genes on Nipponbare reference genome IRGSP-1.0. The xa-45(t) gene provides durable resistance against all the ten Xanthomonas pathotypes of Northern India, thus aiding in the expansion of recessive bacterial blight resistance gene pool. Punjab Rice PR127, carrying xa-45(t), was released for wider use in breeding programs. This study aims to precisely locate the target gene among the 9 candidates conferring resistance to bacterial blight disease. METHODS AND RESULTS: Sanger sequencing of all nine candidate genes revealed seven SNPs and an Indel between the susceptible parent Pusa 44 and the resistant introgression line IL274. The genotyping with polymorphic markers identified three recombinant breakpoints for LOC_Os08g42370, and LOC_Os08g42400, 15 recombinants for LOC_Os08g423420 and 26 for LOC_Os08g42440 out of 190 individuals. Relative expression analysis across six time intervals (0, 8, 24, 48, 72, and 96 h) after bacterial blight infection showed over expression of LOC_Os08g42410-specific transcripts in IL274 compared to Pusa 44, with a significant 4.46-fold increase observed at 72 h post-inoculation. CONCLUSIONS: The Indel marker at the locus LOC_Os08g42410 was found co-segregating with the phenotype, suggesting its candidacy towards xa-45(t). The transcript abundance assay provides strong evidence for the involvement of LOC_Os08g42410 in the resistance conferred by the bacterial blight gene xa-45(t).

Genome analysis and classification of Xanthomonas bacteriophage AhaSv, a new member of the genus Salvovirus.

Xanthomonas phage AhaSv was isolated from lake water. Genome sequencing showed that its genome is a linear dsDNA molecule with a length of 55,576 bp and a G+C content of 63.23%. Seventy-one open reading frames (ORFs) were predicted, and no tRNAs were found in the genome. Phylogenetic analysis showed that AhaSv is closely related to members of the genus Salvovirus of the family Casjensviridae. Intergenomic similarity values between phage AhaSv and homologous phages were up to 90.6%, suggesting that phage AhaSv should be considered a member of a new species in the genus Salvovirus.

Bisdechlorogeodin from antarctic Pseudogymnoascus sp. LAMAI 2784 for citrus canker control.

AIMS: Citrus canker caused by Xanthomonas citri subsp. citri (X. citri) is a disease of economic importance. Control of this disease includes the use of metallic copper, which is harmful to the environment and human health. Previous studies showed that the crude extract from the fungus Pseudogymnoascus sp. LAMAI 2784 isolated from Antarctic soil had in vitro antibacterial action against X. citri. The aim of the present study was to expand the applications of this extract. METHODS AND RESULTS: In greenhouse assays, the crude extract was able to reduce bacterial infection on citrus leaves from 1.55 lesions/cm2 (untreated plants) to 0.04 lesions/cm2. Bisdechlorogeodin was identified as the main compound of the bioactive fraction produced by Pseudogymnoascus sp. LAMAI 2784, which inhibited bacterial growth in vitro (IC90 ≈ 156 µg ml-1) and permeated 80% of X. citri cells, indicating that the membrane is the primary target. CONCLUSION: The present results showed that the bioactive fraction of the extract is mainly composed of the compound bisdechlorogeodin, which is likely responsible for the biological activity against X. citri, and the main mechanism of action is the targeting of the cell membrane. This study indicates that bisdechlorogeodin has valuable potential for the control of X. citri.

Genome-wide identification and characterization of the sweet orange (Citrus sinensis) basic helix-loop-helix (bHLH) family reveals a role for CsbHLH085 as a regulator of citrus bacterial canker resistance.

Citrus bacterial canker (CBC) is a harmful bacterial disease caused by Xanthomonas citri subsp. citri (Xcc), negatively impacting citrus production worldwide. The basic helix-loop-helix (bHLH) transcription factor family plays crucial roles in plant development and stress responses. This study aimed to identify and annotate bHLH proteins encoded in the Citrus sinensis genome and explore their involvement and functional importance in regulating CBC resistance. A total of 135 putative CsbHLHs TFs were identified and categorized into 16 subfamilies. Their chromosomal locations, collinearity, and phylogenetic relationships were comprehensively analyzed. Upon Xcc strain YN1 infection, certain CsbHLHs were differentially regulated in CBC-resistant and CBC-sensitive citrus varieties. Among these, CsbHLH085 was selected for further functional characterization. CsbHLH085 was upregulated in the CBC-resistant citrus variety, was localized in the nucleus, and had a transcriptional activation activity. CsbHLH085 overexpression in Citrus significantly enhanced CBC resistance, accompanied by increased levels of salicylic acid (SA), jasmonic acid (JA), reactive oxygen species (ROS), and decreased levels of abscisic acid (ABA) and antioxidant enzymes. Conversely, CsbHLH085 virus-induced gene silencing resulted in opposite phenotypic and biochemical responses. CsbHLH085 silencing also affected the expression of phytohormone biosynthesis and signaling genes involved in SA, JA, and ABA signaling. These findings highlight the crucial role of CsbHLH085 in regulating CBC resistance, suggesting its potential as a target for biotechnological-assisted breeding citrus varieties with improved resistance against phytopathogens.

The OsICS1 is directly regulated by OsWRKY6 and increases resistance against Xanthomonas oryzae pv. oryzae.

KEY MESSAGE: OsICS1 but not OsICS1-L mediates the rice response to Xoo inoculation, with its overexpression increasing resistance against this pathogen. OsICS1 but not OsICS-L is directly upregulated by OsWRKY6. Rice (Oryza sativa) is a staple crop for about half of the global population and is particularly important in the diets of people living in Asia, Latin America, and Africa. This crop is continually threatened by bacterial leaf blight disease caused by Xanthomonas oryzae pv. oryzae (Xoo), which drastically reduces yields; therefore, it is needed to elucidate the plant's resistance mechanisms against Xoo. Isochorismate synthase (ICS1) generates salicylic acid (SA) and increases resistance against bacterial disease. The OsICS1 is differently annotated in rice genome databases and has not yet been functionally characterized in the context of Xoo infection. Here, we report that the expression of the OsICS1 is directly regulated by OsWRKY6 and increases plant resistance against Xoo. Inoculation with Xoo increased the expression of OsICS1 but not that of the long variant of OsICS1 (OsICS1-L). OsWRKY6 directly activated the OsICS1 promoter but not the OsICS1-L promoter. OsICS1 overexpression in rice increased resistance against Xoo through the induction of SA-dependent bacterial defense genes. These data show that OsICS1 promotes resistance against Xoo infection.

[Genetic dissection of rice resistance to bacterial blight].

Bacterial blight, a major disease in rice, poses a serious impact on rice production. In this study, a doubled haploid (DH) population derived from a cross between the introduced japonica cultivar 'Maybelle' and the indica landrace 'Baiyeqiu' was used to investigate the pathogenicity of four pathogen races causing bacterial blight. The results showed that the pathogenicity of all the pathogen races exhibited continuous, transgressive distribution in the DH population. Moreover, strong correlations existed between every two pathogen races, with the correlation coefficients ranging from 0.3 to 0.6. A total of 12 quantitative trait loci (QTLs) distributed on chromosomes 1, 2, 3, 5, 6, 7, 9, and 12 were detected for rice bacterial blight, explaining 4.95% to 16.05% of the phenotype. Among these QTLs, a major QTL located in the interval RM6024-RM163 on chromosome 5 was detected in three pathogen races. In addition, the pyramiding of the positive alleles can apparently improve the rice resistance to bacterial blight. This study is of great significance for broadening the genetic resources with resistance to bacterial blight in China.

[GmAGB1 plays a positive regulatory role in soybean defense responses].

Heterotrimeric GTP-binding protein (G-proteins) complex, which consists of Gα, Gß and Gγ subunits, plays critical roles in defense signaling. Arabidopsis genome contains only a single Gß-encoding gene, AGB1. Loss function of AGB1 in Arabidopsis results in enhanced susceptibility to a wide range of pathogens. However, the function of soybean AGB1 in immunity has not been previously interrogated. Bioinformatic analysis indicated that there are four GmAGB1 homologous genes in soybean genome, sharing homology of 86%-97%. To overcome the functional redundancy of these GmAGB1 homologs, virus-induced gene silencing (VIGS) mediated by the bean pod mottle virus (BPMV) was used to silence these four genes simultaneously. As expected, these four GmAGB1 homologous genes were indeed silenced by a single BPMV-VIGS vector carrying a conserved fragments among these four genes. A dwarfed phenotype was observed in GmAGB1s-silenced soybean plants, suggesting that GmAGB1s play a crucial role in growth and development. Disease resistance analysis indicated that silencing GmAGB1s significantly compromised the resistance of soybean plants against Xanthomonas campestris pv. glycinea (Xag). This reduced resistance was correlated with the decreased accumulation of pathogen-induced reactive oxygen species (ROS) and the reduced activation of GmMPK3 in response to flg22, a conserved N-terminal peptide of flagellin protein. These results indicate that GmAGB1 functions as a positive regulator in disease resistance and GmAGB1 is indispensable for the ROS production and GmMPK3 activation induced by pathogen infection. Yeast two hybrid assay showed that GmAGB1 interacted with GmAGG1, suggesting that an evolutionary conserved heterotrimeric G protein complex similarly functions in soybean.

Nickel oxide nanoparticles: A new generation nanoparticles to combat bacteria Xanthomonas oryzae pv. oryzae and enhance rice plant growth.

Recently, nanotechnology is among the most promising technologies used in all areas of research. The production of metal nanoparticles using plant parts has received significant attention for its environmental friendliness and effectiveness. Therefore, we investigated the possible applications of biological synthesized nickel oxide nanoparticles (NiONPs). In this study, NiONPs were synthesized through biological method using an aqueous extract of saffron stigmas (Crocus sativus L). The structure, morphology, purity, and physicochemical properties of the obtained NPs were confirmed through Scanning/Transmission Electron Microscopy attached with Energy Dispersive Spectrum, X-ray Diffraction, and Fourier transform infrared. The spherically shaped NiONPs were found by Debye Scherer's formula to have a mean dimension of 41.19 nm. The application of NiONPs in vitro at 50, 100, and 200 µg/mL, respectively, produced a clear region of 2.0, 2.2, and 2.5 cm. Treatment of Xoo cell with NiONPs reduced the growth and biofilm formation, respectively, by 88.68% and 83.69% at 200 µg/mL. Adding 200 µg/mL NiONPs into Xoo cells produced a significant amount of ROS in comparison with the control. Bacterial apoptosis increased dramatically from 1.05% (control) to 99.80% (200 µg/mL NiONPs). When compared to the control, rice plants treated with 200 µg/mL NiONPs significantly improved growth characteristics and biomass. Interestingly, the proportion of diseased leaf area in infected plants with Xoo treated with NiONPs reduced to 22% from 74% in diseased plants. Taken together, NiONPs demonstrates its effectiveness as a promising tool as a nano-bactericide in managing bacterial infection caused by Xoo.

Design and Synthesis of Mandelic Acid Derivatives for Suppression of Virulence via T3SS against Citrus Canker.

Citrus canker, a highly contagious bacterial disease caused by Xanthomonas citri subsp. citri (Xcc), poses a substantial threat to citrus crops, leading to serious reductions in fruit yield and economic losses. Most commonly used bactericides against Xcc lead to the rapid development of resistant subpopulations. Therefore, it is imperative to create novel drugs, such as type III secretion system (T3SS) inhibitors, that specifically target bacterial virulence factors rather than bacterial viability. In our study, we designed and synthesized a series of mandelic acid derivatives including 2-mercapto-1,3,4-thiazole. Seven substances were found to reduce the level of transcription of hpa1 without affecting bacterial viability. In vivo bioassays indicated that compound F9 significantly inhibited hypersensitive response and pathogenicity. RT-qPCR assays showed that compound F9 visibly suppressed the expression of Xcc T3SS-related genes as well as citrus canker susceptibility gene CsLOB1. Furthermore, the combination with compound F9 and quorum-quenching bacteria HN-8 can also obviously alleviate canker symptoms.

Genetic and Functional Diversity Help Explain Pathogenic, Weakly Pathogenic, and Commensal Lifestyles in the Genus Xanthomonas.

The genus Xanthomonas has been primarily studied for pathogenic interactions with plants. However, besides host and tissue-specific pathogenic strains, this genus also comprises nonpathogenic strains isolated from a broad range of hosts, sometimes in association with pathogenic strains, and other environments, including rainwater. Based on their incapacity or limited capacity to cause symptoms on the host of isolation, nonpathogenic xanthomonads can be further characterized as commensal and weakly pathogenic. This study aimed to understand the diversity and evolution of nonpathogenic xanthomonads compared to their pathogenic counterparts based on their cooccurrence and phylogenetic relationship and to identify genomic traits that form the basis of a life history framework that groups xanthomonads by ecological strategies. We sequenced genomes of 83 strains spanning the genus phylogeny and identified eight novel species, indicating unexplored diversity. While some nonpathogenic species have experienced a recent loss of a type III secretion system, specifically the hrp2 cluster, we observed an apparent lack of association of the hrp2 cluster with lifestyles of diverse species. We performed association analysis on a large data set of 337 Xanthomonas strains to explain how xanthomonads may have established association with the plants across the continuum of lifestyles from commensals to weak pathogens to pathogens. Presence of distinct transcriptional regulators, distinct nutrient utilization and assimilation genes, transcriptional regulators, and chemotaxis genes may explain lifestyle-specific adaptations of xanthomonads.

Design, Synthesis, Antibacterial Activity, and Mechanisms of Novel Benzofuran Derivatives Containing Disulfide Moieties.

The unsatisfactory effects of conventional bactericides and antimicrobial resistance have increased the challenges in managing plant diseases caused by bacterial pests. Here, we report the successful design and synthesis of benzofuran derivatives using benzofuran as the core skeleton and splicing the disulfide moieties commonly seen in natural substances with antibacterial properties. Most of our developed benzofurans displayed remarkable antibacterial activities to frequently encountered pathogens, including Xanthomonas oryzae pv oryzae (Xoo), Xanthomonas oryzae pv oryzicola (Xoc), and Xanthomonas axonopodis pv citri (Xac). With the assistance of the three-dimensional quantitative constitutive relationship (3D-QSAR) model, the optimal compound V40 was obtained, which has better in vitro antibacterial activity with EC50 values of 0.28, 0.56, and 10.43 µg/mL against Xoo, Xoc, and Xac, respectively, than those of positive control, TC (66.41, 78.49, and 120.36 µg/mL) and allicin (8.40, 28.22, and 88.04 µg/mL). Combining the results of proteomic analysis and enzyme activity assay allows the antibacterial mechanism of V40 to be preliminarily revealed, suggesting its potential as a versatile bactericide in combating bacterial pests in the future.

Antibacterial activity of Cymbopogon species essential oils against Xanthomonas citri and their use in post-harvest treatment for citrus canker management.

Citrus canker is a disease caused by the gram-negative bacterium Xanthomonas citri subp. citri (X. citri), which affects all commercially important varieties of citrus and can lead to significant losses. Fruit sanitization with products such as chlorine-based ones can reduce the spread of the disease. While effective, their use raises concerns about safety of the workers. This work proposes essential oils (EOs) as viable alternatives for fruit sanitization. EOs from Cymbopogon species were evaluated as to their antibacterial activity, their effect on the bacterial membrane, and their ability to sanitize citrus fruit. The in vitro assays revealed that the EOs from C. schoenanthus and C. citratus had a lower bactericidal concentration at 312 mg L-1, followed by 625 mg L-1 for C. martini and C. winterianus. Microscopy assay revealed that the bacterial cell membranes were disrupted after 15 min of contact with all EOs tested. Regarding the sanitizing potential, the EOs with higher proportions of geraniol were more effective in sanitizing acid limes. Fruit treated with C. shoenanthus and C. martini showed a reduction of ∼68% in the recovery of viable bacterial cells. Therefore, these EOs can be used as viable natural alternatives in citrus fruit disinfection.

Comparative transcriptomic profiling of the two-stage response of rice to Xanthomonas oryzae pv. oryzicola interaction with two different pathogenic strains.

BACKGROUND: Two-tiered plant immune responses involve cross-talk among defense-responsive (DR) genes involved in pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI), effector-triggered immunity (ETI) and effector-triggered susceptibility (ETS). Bacterial leaf streak (BLS), caused by Xanthomonas oryzae pv. oryzicola (Xoc) is an important bacterial disease that causes serious threats to rice yield and quality. Transcriptomic profiling provides an effective approach for the comprehensive and large-scale detection of DR genes that participate in the interactions between rice and Xoc. RESULTS: In this study, we used RNA-seq to analyze the differentially expressed genes (DEGs) in susceptible rice after inoculation with two naturally pathogenic Xoc strains, a hypervirulent strain, HGA4, and a relatively hypovirulent strain, RS105. First, bacterial growth curve and biomass quantification revealed that differential growth occurred beginning at 1 day post inoculation (dpi) and became more significant at 3 dpi. Additionally, we analyzed the DEGs at 12 h and 3 days post inoculation with two strains, representing the DR genes involved in the PTI and ETI/ETS responses, respectively. Gene Ontology (GO) functional and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were performed on the common DEGs, which included 4380 upregulated and 4019 downregulated genes and 930 upregulated and 1383 downregulated genes identified for the two strains at 12 h post inoculation (hpi) and 3 dpi, respectively. Compared to those at 12 hpi, at 3 dpi the number of common DEGs decreased, while the degree of differential expression was intensified. In addition, more disease-related GO pathways were enriched, and more transcription activator-like effector (TALE) putative target genes were upregulated in plants inoculated with HGA4 than in those inoculated with RS105 at 3 dpi. Then, four DRs were randomly selected for the BLS resistance assay. We found that CDP3.10, LOC_Os11g03820, and OsDSR2 positively regulated rice resistance to Xoc, while OsSPX3 negatively regulated rice resistance. CONCLUSIONS: By using an enrichment method for RNA-seq, we identified a group of DEGs related to the two stages of response to the Xoc strain, which included four functionally identified DR genes.

Xanthomonas rydalmerensis sp. nov., a non-pathogenic member of Group 1 Xanthomonas.

Five bacterial isolates were isolated from Fragaria × ananassa in 1976 in Rydalmere, Australia, during routine biosecurity surveillance. Initially, the results of biochemical characterisation indicated that these isolates represented members of the genus Xanthomonas. To determine their species, further analysis was conducted using both phenotypic and genotypic approaches. Phenotypic analysis involved using MALDI-TOF MS and BIOLOG GEN III microplates, which confirmed that the isolates represented members of the genus Xanthomonas but did not allow them to be classified with respect to species. Genome relatedness indices and the results of extensive phylogenetic analysis confirmed that the isolates were members of the genus Xanthomonas and represented a novel species. On the basis the minimal presence of virulence-associated factors typically found in genomes of members of the genus Xanthomonas, we suggest that these isolates are non-pathogenic. This conclusion was supported by the results of a pathogenicity assay. On the basis of these findings, we propose the name Xanthomonas rydalmerensis, with DAR 34855T = ICMP 24941 as the type strain.

The timing of bacterial mesophyll infection shapes the leaf chemical landscape.

Chemistry in eukaryotic intercellular spaces is shaped by both hosts and symbiotic microorganisms such as bacteria. Pathogenic microorganisms like barley-associated Xanthomonas translucens (Xt) swiftly overtake the inner leaf tissue becoming the dominant microbial community member during disease development. The dynamic metabolic changes due to Xt pathogenesis in the mesophyll spaces remain unknown. Genomic group I of Xt consists of two barley-infecting lineages: pathovar translucens (Xtt) and pathovar undulosa (Xtu). Xtu and Xtt, although genomically distinct, cause similar water-soaked lesions. To define the metabolic signals associated with inner leaf colonization, we used untargeted metabolomics to characterize Xtu and Xtt metabolism signatures associated with mesophyll growth. We found that mesophyll apoplast fluid from infected tissue yielded a distinct metabolic profile and shift from catabolic to anabolic processes over time compared to water-infiltrated control. The pathways with the most differentially expressed metabolites by time were glycolysis, tricarboxylic acid cycle, sucrose metabolism, pentose interconversion, amino acids, galactose, and purine metabolism. Hierarchical clustering and principal component analysis showed that metabolic changes were more affected by the time point rather than the individual colonization of the inner leaves by Xtt compared to Xtu. Overall, in this study, we identified metabolic pathways that explain carbon and nitrogen usage during host-bacterial interactions over time for mesophyll tissue colonization. This foundational research provides initial insights into shared metabolic strategies of inner leaf colonization niche occupation by related but phylogenetically distinct phyllosphere bacteria. IMPORTANCE: The phyllosphere is a habitat for microorganisms including pathogenic bacteria. Metabolic shifts in the inner leaf spaces for most plant-microbe interactions are unknown, especially for Xanthomonas species in understudied plants like barley (Hordeum vulgare). Xanthomonas translucens pv. translucens (Xtt) and Xanthomonas translucens pv. undulosa (Xtu) are phylogenomically distinct, but both colonize barley leaves for pathogenesis. In this study, we used untargeted metabolomics to shed light on Xtu and Xtt metabolic signatures. Our findings revealed a dynamic metabolic landscape that changes over time, rather than exhibiting a pattern associated with individual pathovars. These results provide initial insights into the metabolic mechanisms of X. translucens inner leaf pathogenesis.

Xanthomonas Phage PBR31: Classifying the Unclassifiable.

The ability of bacteriophages to destroy bacteria has made them the subject of extensive research. Interest in bacteriophages has recently increased due to the spread of drug-resistant bacteria, although genomic research has not kept pace with the growth of genomic data. Genomic analysis and, especially, the taxonomic description of bacteriophages are often difficult due to the peculiarities of the evolution of bacteriophages, which often includes the horizontal transfer of genes and genomic modules. The latter is particularly pronounced for temperate bacteriophages, which are capable of integration into the bacterial chromosome. Xanthomonas phage PBR31 is a temperate bacteriophage, which has been neither described nor classified previously, that infects the plant pathogen Xanthomonas campestris pv. campestris. Genomic analysis, including phylogenetic studies, indicated the separation of phage PBR31 from known classified bacteriophages, as well as its distant relationship with other temperate bacteriophages, including the Lederbervirus group. Bioinformatic analysis of proteins revealed distinctive features of PBR31, including the presence of a protein similar to the small subunit of D-family DNA polymerase and advanced lysis machinery. Taxonomic analysis showed the possibility of assigning phage PBR31 to a new taxon, although the complete taxonomic description of Xanthomonas phage PBR31 and other related bacteriophages is complicated by the complex evolutionary history of the formation of its genome. The general biological features of the PBR31 phage were analysed for the first time. Due to its presumably temperate lifestyle, there is doubt as to whether the PBR31 phage is appropriate for phage control purposes. Bioinformatics analysis, however, revealed the presence of cell wall-degrading enzymes that can be utilised for the treatment of bacterial infections.

Application and Mechanism of Cryptolepine and Neocryptolepine Derivatives as T3SS Inhibitors for Control of Bacterial Leaf Blight on Rice.

Bacterial leaf blight (BLB) caused by Xanthomonas oryzae pv oryzae (Xoo) is extremely harmful to rice production. The traditional control approach is to use bactericides that target key bacterial growth factors, but the selection pressure on the pathogen makes resistant strains the dominant bacterial strains, leading to a decline in bactericidal efficacy. Type III secretion system (T3SS) is a conserved and critical virulence factor in most Gram-negative bacteria, and its expression or absence does not affect bacterial growth, rendering it an ideal target for creating drugs against Gram-negative pathogens. In this work, we synthesized a range of derivatives from cryptolepine and neocryptolepine. We found that compound Z-8 could inhibit the expression of Xoo T3SS-related genes without affecting the growth of bacteria. an in vivo bioassay showed that compound Z-8 could effectively reduce the hypersensitive response (HR) induced by Xoo in tobacco and reduce the pathogenicity of Xoo in rice. Furthermore, it exhibited synergy in control of bacterial leaf blight when combined with the quorum quenching bacterial F20.