Xanthomonas Oryzae Pv Research Articles

Exploring actinomycetes and endophytes of rice ecosystem for induction of disease resistance against bacterial blight of rice

Biocontrol agents and plant growth promoting microbes have emerged as promising tools for the management of plant diseases and in sustainable crop production. The present study was made to explore the potential metabolites of actinomycetes and endophytes of rice (Oryza sativa L.) and to assay the induced defence reactions in rice plants against bacterial blight (BB) of rice (Xanthomonas oryzae pv. oryzae). In-vitro studies revealed that few promising rhizospheric Streptomyces (S. fimicarius and S. laurentii) and endophytes (Pseudomonas putida and Metarhizium anisopliae) could suppress Xoo effectively in dual culture assay. P. putida + S. fimicarius + S. laurentii showed the highest (58.71%) inhibition of BB. Multiple growth promoting characteristics were assayed for these effective isolates. The effectiveness of the cell suspension (107 cfu/ml) of P. putida, M. anisopliae, S. fimicarius and S. laurentii in suppressing BB of rice was tested in planta by applying as seed treatment, root treatment, soil treatment and spray application. Lowest disease incidence was observed in plants treated with the combination of P. putida + S. fimicarius + S. laurentii (10.29%) as compared to other treatments. To understand the resistance mechanisms of rice plants against Xoo, few effective secondary metabolites were assayed where the total phenol content of the treated plants showed higher concentration (2.52%). Antibiotics were recorded at a higher peak of retention time, such as pyrisulfoxin B (12.26 min), APHE 4 (13.42 min), kanamycin C (22.22 min), nitracidomycin B (15.40 min), clavulanic acid (7.89 min), neothramycin A (16.22 min), nitracidomycin A (17.78 min) and furaquinocin E (24.74 min).

Silver, Gold, and Silver-Gold Bimetallic Nanoparticle-Decorated Dextran: Facile Synthesis and Versatile Tunability on the Antimicrobial Activity

The noble metal-based nanoparticles (NPs) have been considered as potential antimicrobial agents because of their good antibacterial and antifungal activities as well as biocompatible nature. In this study, we have introduced a simple and fast route to synthesize silver, gold, and silver-gold bimetallic NP-decorated dextran. The as-synthesized noble metal-based NPs with spherical geometry showed high dispersity in dextran. The antibacterial and antifungal of obtained nanomaterials were tested with Xanthomonas oryzae pv. oryzae (Xoo) bacteria and Magnaporthe grisea (M. grisea) fungi. The silver NPs and bimetallic NPs with high silver content in dextran exhibited excellent activity to inhibited the growth of the bacteria and fungi, whereas the gold/dextran has weak antimicrobial effects. The antibacterial and antifungal properties of silver-gold bimetallic NPs in dextran biopolymer can be tuned according to the content of silver in the bimetallic NPs. The obtained nanomaterials could open an entry to a new class of antibiotics.

Rice glutaredoxin GRXS15 confers broad-spectrum resistance to Xanthomonas oryzae pv. oryzae and Fusarium fujikuroi

Rice is a particularly widely consumed food crop globally, but its yield is seriously damaged by bacterial blight due to Xanthomonas oryzae pv. oryzae (Xoo) and bakanae disease due to Fusarium fujikuroi (F. fujikuroi). However, broad-spectrum resistance (BSR) to both Xoo and F. fujikuroi remains largely elusive. In this study, we showed that rice monothiol glutaredoxin GRXS15 localizes in mitochondria and the nucleus, and its transcription is induced by Xoo. Transgenic rice lines constitutively expressing OsGRXS15 showed enhanced disease resistance to Xoo and F. fujikuroi, while CRISPR/Cas9-based knockout mutants showed reduced resistance compared with the wild-type plants. The transcription of pathogenesis-related (PR) genes was significantly induced in OsGRXS15-expressing plants. The rice transcription factor OsWRKY65 was identified as a binding partner, and it directly interacted with OsGRXS15 in the nucleus. Moreover, we revealed that the interaction of OsGRXS15 and OsWRKY65 results in the upregulation of OsPR1. These results suggested that OsGRXS15 interacts with transcription factors, and it confers BSR through regulating the expression of genes related to pathogen response. This is the first report on the nuclear function associated with the monothiol glutaredoxin GRXS15.

Bioinspired Green Synthesis of Chitosan and Zinc Oxide Nanoparticles with Strong Antibacterial Activity against Rice Pathogen Xanthomonas oryzae pv. oryzae.

Bacterial leaf blight caused by Xanthomonas oryzae pv. oryzae (Xoo) is one of the most devastating diseases, resulting in significant yield losses in rice. The extensive use of chemical antibacterial agents has led to an increase the environmental toxicity. Nanotechnology products are being developed as a promising alternative to control plant disease with low environmental impact. In the present study, we investigated the antibacterial activity of biosynthesized chitosan nanoparticles (CSNPs) and zinc oxide nanoparticles (ZnONPs) against rice pathogen Xoo. The formation of CSNPs and ZnONPs in the reaction mixture was confirmed by using UV-vis spectroscopy at 300–550 nm. Moreover, CSNPs and ZnONPs with strong antibacterial activity against Xoo were further characterized by scanning and transmission electron microscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction. Compared with the corresponding chitosan and ZnO alone, CSNPs and ZnONPs showed greater inhibition in the growth of Xoo, which may be mainly attributed to the reduction in biofilm formation and swimming, cell membrane damage, reactive oxygen species production, and apoptosis of bacterial cells. Overall, this study revealed that the two biosynthesized nanoparticles, particularly CSNPs, are a promising alternative to control rice bacterial disease.

A bacterial F-box effector suppresses SAR immunity through mediating the proteasomal degradation of OsTrxh2 in rice.

Plant bacterial pathogens usually cause diseases by secreting and translocating numerous virulence effectors into host cells and suppressing various host immunity pathways. It has been demonstrated that the extensive ubiquitin systems of host cells are frequently interfered with or hijacked by numerous pathogenic bacteria, through various strategies. Some type-III secretion system (T3SS) effectors of plant pathogens have been demonstrated to impersonate the F-box protein (FBP) component of the SKP1/CUL1/F-box (SCF) E3 ubiquitin system for their own benefit. Although numerous putative eukaryotic-like F-box effectors have been screened for different bacterial pathogens by bioinformatics analyses, the targets of most F-box effectors in host immune systems remain unknown. Here, we show that XopI, a putative F-box effector of African Xoo (Xanthomonas oryzae pv. oryzae) strain BAI3, strongly inhibits the host's OsNPR1-dependent resistance to Xoo. The xopI knockout mutant displays lower virulence in Oryza sativa (rice) than BAI3. Mechanistically, we identify a thioredoxin protein, OsTrxh2, as an XopI-interacting protein in rice. Although OsTrxh2 positively regulates rice immunity by catalyzing the dissociation of OsNPR1 into monomers in rice, the XopI effector serves as an F-box adapter to form an OSK1-XopI-OsTrxh2 interaction complex, and further disrupts OsNPR1-mediated resistance through proteasomal degradation of OsTrxh2. Our results indicate that XopI targets OsTrxh2 and further represses OsNPR1-dependent signaling, thereby subverting systemic acquired resistance (SAR) immunity in rice.

Sunlight-Induced Synthesis of Non-Target Biosafety Silver Nanoparticles for the Control of Rice Bacterial Diseases.

Silver is an important and efficient bactericide. Nanoscale silver has a large specific surface area, high target adhesion, strong permeability and high bactericidal activity. At present, the control of plant bacterial diseases is difficult, and the resistance of plant bacterial pathogens develops rapidly. Silver nanoparticles are expected to become a new generation of agrochemical to control plant bacterial diseases. In this study, a simple and green natural sunlight-induced method was used to prepare carboxymethylcellulose sodium-stabilized silver nanoparticles (CMC-SNs) with a particle size of around 13.53 ± 4.72 nm. CMC-SNs were characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), energy-dispersive spectrometry (EDS), X-ray diffraction (XRD) and UV-vis spectroscopy and found to be spherical and evenly dispersed. The bacteriostatic activity of the CMC-SNs toward Xanthomonas oryzae pv. oryzae (Xoo) was tested. The minimum inhibitory concentration (MIC) of CMC-SNs to Xoo was 1 mg/L, and the minimum bactericidal concentration (MBC) was 2 mg/L. In addition, the antibacterial mechanism was studied by scanning electron microscope (SEM) and confocal laser scanning microscope (CLSM), which confirmed that the CMC-SNs had high antibacterial activity. In order to verify its impact on the environment, we conducted an acute toxicity test on zebrafish and found that Half lethal concentration (LC50) > 100 mg/L in zebrafish, or no acute toxicity. The ability of CMC-SNs to control rice bacterial blight was verified by a pot experiment.

Rice transcription factor WRKY114 directly regulates the expression of OsPR1a and Chitinase to enhance resistance against Xanthomonas oryzae pv. oryzae

Rice (Oryza sativa L.) is a global staple crop, but its yield is severely threatened by bacterial leaf blight (BLB) caused by Xanthomonas oryzae pv. oryzae (Xoo). The OsWRKY transcription factor family play a central role in innate plant immunity against Xoo, but the various biological functions of a large number of OsWRKYs remain to be understood. We characterized the role of OsWRKY114 against Xoo. OsWRKY114 has transcriptional activity in yeast and localizes in the nucleus. When OsWRKY114 is overexpressed in transgenic plants they show enhanced disease resistance against Xoo compared with wild types. By using genetic- and cell-based functional analyses, we showed OsWRKY114 directly associates with the promoters of OsPR1a and Chitinase and increases the promoter activities. These results suggest that OsWRKY114 enhances the innate immunity of Asian rice against Xoo through direct activation of defense genes that include OsPR1a and chtinase. This is the first report to functionally characterize OsWRKY114 in Xoo infection.

Seed treatment and foliar application of methyl salicylate (MeSA) as a defense mechanism in rice plants against the pathogenic bacterium, Xanthomonas oryzae pv. oryzae

Methyl salicylate (MeSA) is a volatile biological compound synthesized from salicylic acid (SA) and is a plant hormone that helps defend against pests and pathogens. A major bacterial pathogen of rice, Xanthomonas oryzae pv. oryzae (Xoo) causes severe disease. Seed and plant treatments with MeSA can stimulate the defense enzyme peroxidase (POD) in plants. Response of peroxidase activity in rice (Oryza sativa L) cultivars IR 20, IR 50, IR 64, ASD 16, ASD 19 and ADT 46 to MeSA were measured under greenhouse conditions. Treatments of rice seedlings with MeSA at 50 and 100 mg L−1 significantly upregulated POD expression in the plants. The activity of POD was also significantly upregulated when plants were inoculated with bacterial blight. Effects were stronger in ASD 16, ASD 19 and ADT 46 and were more pronounced in high dose treatment (100 mg L−1) when inoculated with bacterial blight condition and the effects were dose dependent, although the relationship between dose and rice varieties were not always linear. The pathogenic related (PR) protein bands at 33 kDa and 14 kDa were identified in treatments of 100 mg L−1 MeSA in the presence of bacterial blight disease. Band intensity was estimated to be twice that of those from pathogen induce MeSA levels in rice plants. These results suggest that treatment with MeSA can significantly increase the POD defense related enzyme by altering the plant physiology in ways that may be beneficial for crop protection.

Phytochemical profiling and antimicrobial activity of ginger (Zingiber officinale) essential oils against important phytopathogens

The objectives of this study were to profile ginger essential oils (EOs) phytochemical constituents and antimicrobial activity against important phytopathogens. Ginger EOs was extracted using a modified Clevenger-type apparatus by hydro-distillation then followed by GCMS and headspace analysis of its phytochemical constituents. The phytoconstituents identified were monoterpenes and sesquiterpene hydrocarbons. Food poisoned and disc diffusion techniques were applied to determine the percentage inhibition of fungal mycelial and bacterial growth respectively. The EOs produced mycelial growth inhibition in all the test fungal pathogens after five days of incubation. The MIC and MFC of the EOs on the tested fungi were in the range of 1 μl/ml and 5–6 μl/ml, respectively. The bacterial growth of all the tested isolates was also affected by EOs at 100–500 µl/ml, from weak to strong antibacterial activity. The EOs affected the Xanthomonas oryzae pv. oryzae-strain A isolate mostata higher concentration of 400–500 μl/ml with mean inhibition of 20.66 mm and 22.66 mm respectively, which are found to be effective. The MIC values on the bacterial pathogens were at100 μl/ml. The inhibition zone of positive control (streptomycin) at 15 µg/disc was 25.00 mm and appeared to be efficient. Metabolomics analysis to concurrently quantify variability among multiple compounds in the data sets and identify such compounds responsible for the X. oryzae pv. oryzae-strain-A inhibition were determined. The cross-validated PLS model has shown a strong correlation between ginger EOs and bioactivity. The action of ginger EOs on the cell structure was fully identified using SEM by observing the changes in morphology and integrity of X. oryzae pv. oryzae-strain-A cells. The DMSO treatment (control) showed a normal rod shape cell, while treatment with the ginger EOs showed irregular shape with sunken surfaces, and treatment with antibiotics display abnormal growth of the cells. These findings can, therefore, propose that the ginger EOs could be used as a new antimicrobial agent in suppressing the growth of phytopathogens and as possible new alternatives to synthetic fungicides and bactericides.

Identification of responsive genes and analysis of genes with bacterial-inducible cis-regulatory elements in the promoter regions in Oryza sativa L.

Bacterial blight of rice caused by Xanthomonas oryzae pv. oryzae (Xoo) is one of the most critical diseases in rice. In order to study rice responsive genes to bacterial stress, microarray data were retrieved from GEO dataset. To identify the responsive genes to biotic stress (bacteria) bioinformatic tools were employed and the data presented in the forms of heatmap, gene ontology, gene network, and cis-element prediction were used. Almost all responsive genes were down-regulated at around 3 h time point and up-regulated 24 h time point in response to bacterial stress in rice varieties (Oryza sativa subs. japonica ‘IR64’, ‘IRBB5’, ‘IRBB7’ and ‘Y73’). Gene ontology showed that genes are involved in different biological processes including translation and cellular protein metabolic processes. Network analysis showed that genes expressed in response to pathogen infection (Xoo) included protein translation, eukaryotic initiation factors (eIFs), ribosomal proteins, protein ubiquitin, and MAPK genes. The genes expressed in response to bacterial stress can enable plant balance between synthesis and degradation of proteins which in turn allows plants for further growth and development. TATA-box and CAAT box had the highest number of cis elements involved in bacterial stress. These genes can provide novel insights into regulatory mechanisms in biotic stress responses in rice. Identification of bacterial stress response/tolerance genes of rice can assist the molecular breeding of new rice varieties tolerant to bacterial stress.

Synthesis and antibacterial activity of novel myricetin derivatives containing sulfonylpiperazine

Myricetin derivatives containing sulfonylpiperazine were synthesized and their structures were confirmed by NMR and HRMS. The antibacterial activity results indicated that some compounds showed good antibacterial activity against Xanthomonas oryzaepv. oryzae (Xoo), Xanthomonas axonopodispv. citri (Xac) and Ralstonia solanacearum (Rs). Among them, compounds 4m and 4p revealed excellent antibacterial activities against Rs with a concentration for 50% of maximal effect (EC50) value of 4 and 4 μg/mL, which were better than the control drugs bismerthiazol (13 μg/mL) and thiodiazole-copper (185 μg/mL). As observed using scanning electron microscope (SEM), these compounds act by causing folding and deformation of the bacterial surface, resulting in incomplete bacterial structure, so as to achieve the goal of bacteriostasis. The myricetin derivatives synthesized are expected to guide the research direction of new antibacterial agents.

Mycosynthesis of ZnO Nanoparticles Using Trichoderma spp. Isolated from Rhizosphere Soils and Its Synergistic Antibacterial Effect against Xanthomonas oryzae pv. oryzae.

The Plant Growth Promoting Fungi (PGPF) is used as a source of biofertilizers due to their production of secondary metabolites and beneficial effects on plants. The present work is focused on the co-cultivation of Trichoderma spp. (T. harzianum (PGT4), T. reesei (PGT5) and T. reesei (PGT13)) and the production of secondary metabolites from mono and co-culture and mycosynthesis of zinc oxide nanoparticles (ZnO NPs), which were characterized by a UV visible spectrophotometer, Powder X-ray Diffraction (PXRD), Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) with Energy Dispersive Spectroscopy (EDAX) and Transmission Electron Microscope (TEM) and Selected Area (Electron) Diffraction (SAED) patterns. The fungal secondary metabolite crude was extracted from the mono and co-culture of Trichoderma spp. And were analyzed by GC-MS, which was further subjected for antibacterial activity against Xanthomonas oryzae pv. Oryzae, the causative organism for Bacterial Leaf Blight (BLB) in rice. Our results showed that the maximum zone of inhibition was recorded from the co-culture of Trichoderma spp. rather than mono cultures, which indicates that co-cultivation of beneficial fungi can stimulate the synthesis of novel secondary metabolites better than in monocultures. ZnO NPs were synthesized from fungal secondary metabolites of mono cultures of Trichoderma harzianum (PGT4), Trichoderma reesei (PGT5), Trichoderma reesei (PGT13) and co-culture (PGT4 + PGT5 + PGT13). These ZnO NPs were checked for antibacterial activity against Xoo, which was found to be of a dose-dependent manner. In summary, the biosynthesized ZnO NPs and secondary metabolites from co-culture of Trichoderma spp. are ecofriendly and can be used as an alternative for chemical fertilizers in agriculture.

Advances in the Xoo-rice pathosystem interaction and its exploitation in disease management

Bacterial blight caused by Xanthomonas oryzae pv. oryzae (Xoo), is one of the devastating diseases of rice worldwide. The pathogen reported to cause 70% crop loss in some of the susceptible genotypes under disease favoring environments, viz., temperature ranging between 25 to 34°C and relative humidity more than 70%. In Xoo, about 245 genes govern the pathogenicity and host specificity. The hypersensitive response and pathogenicity (hrp) genes responsible for disease occurrence were clustered in the pathogenicity island of 31.3 Kb. The protein secreted through type three secretory system and type one secretory system mediates infection and establishment of the pathogen inside the host. However, elicitor molecules from Xoo triggered the resistant response in rice against the pathogen. An array of resistant genes (R genes) was known to be invoked by the host to combat the bacterial infection. To date, of the 45 Xa genes in rice, nine were cloned and characterized. The evolution of new races has made the task of developing resistant rice genotypes more challenging as it demands a comprehensive breeding strategy involving the best use of R genes from the existing gene pool. Thus, to combat the infection from the existing races and to slow down the emergence of new Xoo races, pyramiding two or more R genes was found to be effective against bacterial blight disease. In India, the successfully commercialized example includes the development of rice genotypes, viz., Improved Pusa Basmati- 1, Improved Samba Mahsuri, PR106, Type 3 Basmati, and Mahsuri with selected R genes, viz., xa5, Xa4, xa13 and Xa21 against bacterial blight resistance. This review primarily portray Xoo-rice interactions and provides opportunities for its effective management through sustainable technologies.

Cloning of the Rice Xo1 Resistance Gene and Interaction of the Xo1 Protein with the Defense-Suppressing Xanthomonas Effector Tal2h.

The Xo1 locus in the heirloom rice variety Carolina Gold Select confers resistance to bacterial leaf streak and bacterial blight, caused by Xanthomonas oryzae pv. oryzicola and X. oryzae pv. oryzae, respectively. Resistance is triggered by pathogen-delivered transcription activator-like effectors (TALEs) independent of their ability to activate transcription and is suppressed by truncated variants called truncTALEs, common among Asian strains. By transformation of the susceptible variety Nipponbare, we show that one of 14 nucleotide-binding, leucine-rich repeat (NLR) protein genes at the locus, with a zinc finger BED domain, is the Xo1 gene. Analyses of published transcriptomes revealed that the Xo1-mediated response is more similar to those mediated by two other NLR resistance genes than it is to the response associated with TALE-specific transcriptional activation of the executor resistance gene Xa23 and that a truncTALE dampens or abolishes activation of defense-associated genes by Xo1. In Nicotiana benthamiana leaves, fluorescently tagged Xo1 protein, like TALEs and truncTALEs, localized to the nucleus. And endogenous Xo1 specifically coimmunoprecipitated from rice leaves with a pathogen-delivered, epitope-tagged truncTALE. These observations suggest that suppression of Xo1-function by truncTALEs occurs through direct or indirect physical interaction. They further suggest that effector coimmunoprecipitation may be effective for identifying or characterizing other resistance genes.

Synthesis and biological evaluation of 1,4-pentadien-3-one derivatives containing 1,2,4-triazole

A series of new 1,4-pentadien-3-one derivatives containing 1,2,4-triazole moiety were synthesized. The structures of the synthesized compounds were charactered via 1H NMR, 13C NMR and HRMS. Antibacterial bioassays indicated that some of compounds showed potential antibacterial activities against Ralstonia solanacearum (Rs), Xanthomonas oryzae pv. Oryzae (Xoo) and Xanthomonas axonopodis pv. Citri (Xac). Compounds F8 and F17 showed good in vitro antibacterial activities against Rs, with the EC50 values of 18.6 and 18.6 μg/mL, respectively, which were better than commercial agent bismerthiazol (55.2 μg/mL). Furthermore, compounds F12 and F15 showed good in vitro antibacterial activities against Xoo, with the EC50 values of 10.9 and 17.5 μg/mL, which were better than commercial agent bismerthiazol (69.3 μg/mL). Moreover, compounds F2, F9, F16 and F17 showed good in vitro antibacterial activities against Xac, with the EC50 values of 6.6, 5.4, 7.5 and 7.8 μg/mL, respectively, which were better than commercial agent bismerthiazol (54.9 μg/mL). The effect of compound F9 on Xac bacterial cell membrane rupture was observed by scanning electron microscopy (SEM). In addition, antiviral bioassays indicated that some of compounds showed excellent protection activities against tobacco mosaic virus (TMV). Compounds F5 and F15 showed good protecting activity against TMV, with the EC50 values of 108.3 and 105.4 μg/mL, respectively, which were better than commercial agent ningnanmycin (214.7 μg/mL). Microscale thermophoresis (MST) also showed that the binding of compound F2 to TMV coat protein (TMV-CP) yielded a Kd value of 1.260 ± 0.654 μmol/L, which was very close to ningnanmycin (1.058 ± 0.286 μmol/L). Similarly, the molecular docking studies for F2 and F5 with TMV-CP (PDB code: 1EI7, ID: 4QGH) indicated that compounds F2 and F5 had partially interacted with TMV-CP.

Diversity of resistance to bacterial blight and geographical distribution of 29 populations of wild rice [Oryza meyeriana (Zoll. & Moritzi) Baill.] in Yunnan, China

Oryza meyeriana (Zoll. & Moritzi) Baill. is a wild relative of cultivated rice. O. meyeriana is reported to exhibit high resistance or immunity to bacterial blight (BB), a disease caused by Xanthomonas oryzae pv. Oryzae (Xoo). To fully understand the BB resistance of O. meyeriana across multiple distribution sites in Yunnan, China, 87 accessions of 29 O. meyeriana populations were inoculated by artificial leaf cutting with the Xoo virulent strain CX28-3 isolated from rice in Yunnan. The diversity of resistance and habitat of each accession were then analysed. The results showed that resistance was variable. Among the 87 accessions, only 20.7% were resistant (12 resistant and 6 highly resistant), 37.9% were susceptible (9 highly susceptible and 24 susceptible), and the remaining 41.4% (36 accessions) were moderately resistant; no accession tested displayed immunity to CX28-3. The variation of resistance among populations is higher than within a population. The 29 populations of O. meyeriana were divided into categories according to administrative region, river system, longitude, latitude, altitude and climate factors. The resistance distribution and diversity index of the 29 O. meyeriana populations were calculated. The resistance of O. meyeriana accessions was shown to be quite different among the five administrative regions. The resistance from Xishuangbanna was the strongest, followed by Pu’er, Dehong, and Lincang, while that from Baoshan was the weakest. The diversity index of resistance is highest in Pu’er (1.13), followed by Dehong (0.95), Baoshan (0.69), Lincang (0.67), and Xishuangbanna (0.64). Correlation analysis showed that geographical and climatic factors impacted the resistance of O. meyeriana. There is a highly significant positive correlation between latitude and disease index. There is also a significant positive correlation between altitude and disease index. These results indicate that accessions of O. meyeriana at greater latitude or altitude are more susceptible to BB. By cluster analysis of the geographical and climatic factors of the O. meyeriana distribution sites, the 29 populations were classified into five groups with differences in resistance. O. meyeriana is considered nearly immune to BB, but susceptible accessions were found for the first time in Yunnan Province, China.

Assessment of Bacterial Leaf Blight Disease of Indonesian Rice Germplasms Using SSR Markers

Bacterial leaf blight (BLB) caused by Xanthomonas oryzae pv. oryzae (Xoo) is a serious disease in rice plants worldwide. Yield losses caused by Xoo can be as high as 50% in some parts of Asia. Xa7 gene can potentially confer a broad resistance to BLB. Evaluation of disease resistance characteristics in early breeding generations of rice is important to develop varieties with better resistance. This study reports the evaluation of 167 Indonesian rice germplasms against three BLB isolates/pathotypes in a green house setting and the genotyping of 56 Indonesian rice germplasm using 12 SSR markers linked to Xa7 BLB resistance gene. The majority of the indigenous rice germplasms was found to be susceptible to three BLB isolates/pathotypes tested. Sate Liko from Bantul, Yogyakarta, Horeg from Cirebon, West Java and Sijem from Malang, East Java revealed consistent resistance to three isolates/pathotypes tested based on BLB evaluation in a greenhouse, UPGMA analysis, and genotyping. Pathotype XII displayed more virulence to Indonesian rice varieties tested compared to pathotypes VI and V. The association analysis using the General linear model identified six markers associated with BLB resistance and two markers were highly associated (RM20589 and RM20590). This information will be useful for future studies of BLB resistance in rice plants.

Design and synthesis of novel 1,3,4-oxadiazole sulfone compounds containing 3,4-dichloroisothiazolylamide moiety and evaluation of rice bacterial activity

In this study, thirty 1,3,4-oxadiazole sulfone derivatives containing 3,4-dichloroisothiazolamide moiety were designed and synthesized, and their antibacterial activities were evaluated. Bioassay results showed that some compounds exhibited excellent antibacterial activities against Xanthomonas oryzae pv. oryzae (Xoo) and Xanthomonas oryzae pv. oryzicola (Xoc) in vitro and in vivo. Notably, the EC50 values of compounds 2 and 3 against Xoo were 0.79 and 0.85 μg/mL, respectively, which were superior to those of the control agents isotianil, bismerthiazol, and thiodiazole copper. In addition, in vivo antibacterial activities revealed that the compound 2 at 50 μg/mL possessed protective and curative activities of 43.99% and 41.06% against Xoo, respectively, which were better than positive controls. Furthermore, the preliminary mechanism study disclosed that compound 2 exhibited effective antibacterial activity against Xoo by inhibiting the formation of extracellular polysaccharides from Xoo, increasing cell permeability, and changing the shape of cells. This study suggested that 1,3,4-oxadiazole sulfone derivatives containing 3,4-dichloroisothiazolamide moiety displayed excellent antibacterial activity and could be further explored and developed as commercial pesticides.

A-to-I RNA editing in bacteria increases pathogenicity and tolerance to oxidative stress.

Adenosine-to-inosine (A-to-I) RNA editing is an important posttranscriptional event in eukaryotes; however, many features remain largely unexplored in prokaryotes. This study focuses on a serine-to-proline recoding event (S128P) that originated in the mRNA of fliC, which encodes a flagellar filament protein; the editing event was observed in RNA-seq samples exposed to oxidative stress. Using Sanger sequencing, we show that the S128P editing event is induced by H2O2. To investigate the in vivo interaction between RNAs and TadA, which is the principal enzyme for A-to-I editing, genome-wide RNA immunoprecipitation–coupled high-throughput sequencing (iRIP-Seq) analysis was performed using HA-tagged TadA from Xanthomonas oryzae pv. oryzicola. We found that TadA can bind to the mRNA of fliC and the binding motif is identical to that previously reported by Bar-Yaacov and colleagues. This editing event increased motility and enhanced tolerance to oxidative stress due to changes in flagellar filament structure, which was modelled in 3D and measured by TEM. The change in filament structure due to the S128P mutant increased biofilm formation, which was measured by the 3D laser scanning confocal microscopy. RNA-seq revealed that a gene cluster that contributes to siderophore biosynthesis and Fe3+ uptake was upregulated in S128P compared with WT. Based on intracellular levels of reactive oxygen species and an oxidative stress survival assay, we found that this gene cluster can contribute to the reduction of the Fenton reaction and increases biofilm formation and bacterial virulence. This oxidative stress response was also confirmed in Pseudomonas putida. Overall, our work demonstrates that A-to-I RNA editing plays a role in bacterial pathogenicity and adaptation to oxidative stress.

Design, Synthesis, Crystal Structure, and Antimicrobial Evaluation of 6-Fluoroquinazolinylpiperidinyl-Containing 1,2,4-Triazole Mannich Base Derivatives against Phytopathogenic Bacteria and Fungi.

A total of 20 1,2,4-triazole Mannich base derivatives bearing the 6-fluoroquinazolinylpiperidinyl moiety were designed, synthesized, and evaluated as antimicrobial agents against phytopathogenic bacteria and fungi according to the molecular hybridization strategy. Of note, the structure of target compound 4h was clearly confirmed through single-crystal X-ray diffraction analysis. The turbidimetric assays indicated that some compounds exhibited excellent antibacterial efficacies in vitro against Xanthomonas oryzae pv. oryzae (Xoo). For example, compounds 4c, 4f, 4j, and 7j had EC50 values of 23.6, 18.8, 23.4, and 24.3 μg/mL, respectively, which were far superior to that of agrobactericide bismerthiazol (EC50 = 92.4 μg/mL). In particular, compound 4f demonstrated a potent anti-Xoo activity approximately five times more active than that of bismerthiazol. Moreover, in vivo assays showed the excellent protective and curative activities of compound 4f against rice bacterial blight, having the potential as an alternative bactericide for controlling Xoo. The structure-activity relationship analysis showed a good pesticide-likeness concerning compound 4f, following Tice's criteria. The anti-Xoo mechanism of compound 4f was preliminarily explored by scanning electron microscopy measurements in living bacteria. Finally, several compounds also exhibited good antifungal activities in vitro against Gibberella zeae at 50 μg/mL. In short, the presented work showed the potential of 6-fluoroquinazolinylpiperidinyl-containing 1,2,4-triazole Mannich base derivatives as effective bactericides for controlling Xoo.