Xanthomonas Oryzae Pv Research Articles

Interplay between the cyclic di-GMP network and the cell-cell signalling components coordinates virulence-associated functions in Xanthomonas oryzae pv. oryzae.

Xanthomonas oryzae pv. oryzae (Xoo) causes a serious disease of rice known as bacterial leaf blight. Several virulence-associated functions have been characterized in Xoo. However, the role of important second messenger c-di-GMP signalling in the regulation of virulence-associated functions still remains elusive in this phytopathogen. In this study we have performed an investigation of 13 c-di-GMP modulating deletion mutants to understand their contribution in Xoo virulence and lifestyle transition. We show that four Xoo proteins, Xoo2331, Xoo2563, Xoo2860 and Xoo2616, are involved in fine-tuning the in vivo c-di-GMP abundance and also play a role in the regulation of virulence-associated functions. We have further established the importance of the GGDEF domain of Xoo2563, a previously characterized c-di-GMP phosphodiesterase, in the virulence-associated functions of Xoo. Interestingly the strain harbouring the GGDEF domain deletion (ΔXoo2563GGDEF ) exhibited EPS deficiency and hypersensitivity to streptonigrin, indicative of altered iron metabolism. This is in contrast to the phenotype exhibited by an EAL overexpression strain wherein, the ΔXoo2563GGDEF exhibited other phenotypes, similar to the strain overexpressing the EAL domain. Taken together, our results indicate a complex interplay of c-di-GMP signalling with the cell-cell signalling to coordinate virulence-associated function in Xoo.

Flavonoids and other phenolics from Camellia nitidissima chi flowers

From Camellia nitidissima Chi flowers four undescribed flavonoids, nitidissimol A, nitidissimol B, sexangularetin 3-O-(6''-trans-p-coumarolyglucopyranoside) and sexangularetin 3-O-(2''-trans-p-coumarolyglucopyranoside) (1–4), and two previously unreported phenolics, nitidissimol C, D (9, 10), were isolated first time along with ten known compounds, kaempferol 3-O-(6’’-O-trans-p-coumaroyl)-β-D- glucopyranoside (5), kaempferol-3-O-rhamnoside (6), Quercetin-3’-O-β-D-glucoside (7), kaempferol-7-O-β-D-glucoside (8), erythro-guaiacylglycerol-O-4’-coniferyl ether (11), threo-guaiacylglycerol-O-4’-coniferyl ether (12), protocatechuic acid (13), 1,2-Diethoxybenzene (14), ethyl shikimate (15), 2,4,6-trihydroxybenzoic acid 4-O-allopyranoside (16). The structures of the isolated compounds were elucidated by spectroscopic analysis of 1 D- and 2 D-NMR and MS data. Moreover, all isolated compounds (1-16) were tested for the antibacterial activity against Xanthomonas oryzae pv. oryzae and their quorum sensing inhibitory activity in Pseudomonas aeruginosa PAO1. However, no one showed signifcant inhibition of X. oryzae pv. oryzae (MIC90 > 0.1 mg/mL), nor did they significantly inhibit the pyocyanin synthesis, which is controlled by quorum sensing in PAO1.

Fabrication of Versatile Pyrazole Hydrazide Derivatives Bearing a 1,3,4-Oxadiazole Core as Multipurpose Agricultural Chemicals against Plant Fungal, Oomycete, and Bacterial Diseases.

Developing multipurpose agricultural chemicals is appealing in crop protection, thus eventually realizing the reduction and efficient usage of pesticides. Herein, an array of versatile pyrazole hydrazide derivatives bearing a 1,3,4-oxadiazole core were initially synthesized and biologically evaluated the antifungal, antioomycetes, and antibacterial activities. In addition, the pyrazole ring was replaced by the correlative pyrrole, thiazole, and indole scaffolds to extend the molecular diversity. The results showed that most of these hybrid compounds were empowered with multifunctional bioactivities, which are exemplified by compounds a1-a6, b1-b3, b7, b10, b13, and b18. For the antifungal activity, the minimal EC50 values could afford 0.47 (a2), 1.05 (a2), 0.65 (a1), and 1.32 μg/mL (b3) against the corresponding fungi Gibberella zeae (G. z.), Fusarium oxysporum, Botryosphaeria dothidea, and Rhizoctonia solani. In vivo pot experiments against corn scab (caused by G. z.) revealed that the compound a2 was effective with protective and curative activities of 90.2 and 86.3% at 200 μg/mL, which was comparable to those of fungicides boscalid and fluopyram. Further molecular docking study and enzymatic activity analysis (IC50 = 3.21 μM, a2) indicated that target compounds were promising succinate dehydrogenase inhibitors. Additionally, compounds b2 and a4 yielded superior anti-oomycete and antibacterial activities toward Phytophora infestins and Xanthomonas oryzae pv. oryzae with EC50 values of 2.92 and 8.43 μg/mL, respectively. In vivo trials against rice bacterial blight provided the control efficiency within 51.2-55.3% (a4) at 200 μg/mL, which were better than that of bismerthiazol. Given their multipurpose characteristics, these structures should be positively explored as agricultural chemicals.

A key antisense sRNA modulates the oxidative stress response and virulence in Xanthomonas oryzae pv. oryzicola

Pathogens integrate multiple environmental signals to navigate the host and control the expression of virulence genes. In this process, small regulatory noncoding RNAs (sRNAs) may function in gene expression as post-transcriptional regulators. In this study, the sRNA Xonc3711 functioned in the response of the rice pathogen, Xanthomonas oryzae pv. oryzicola (Xoc), to oxidative stress. Xonc3711 repressed production of the DNA-binding protein Xoc_3982 by binding to the xoc_3982 mRNA within the coding region. Mutational analysis showed that regulation required an antisense interaction between Xonc3711 and xoc_3982 mRNA, and RNase E was needed for degradation of the xoc_3982 transcript. Deletion of Xonc3711 resulted in a lower tolerance to oxidative stress due to the repression of flagella-associated genes and reduced biofilm formation. Furthermore, ChIP-seq and electrophoretic mobility shift assays showed that Xoc_3982 repressed the transcription of effector xopC2, which contributes to virulence in Xoc BLS256. This study describes how sRNA Xonc3711 modulates multiple traits in Xoc via signals perceived from the external environment.

Design, Synthesis, and Bioactivity Evaluation of New Thiochromanone Derivatives Containing a Carboxamide Moiety.

In this study, using the botanical active component thiochromanone as the lead compound, a total of 32 new thiochromanone derivatives containing a carboxamide moiety were designed and synthesized and their in vitro antibacterial activities against Xanthomonas oryzae pv. oryzae (Xoo), Xanthomonas oryzae pv. oryzicolaby (Xoc), and Xanthomonas axonopodis pv. citri (Xac) were determined, as well as their in vitro antifungal activities against Botryosphaeria dothidea (B. dothidea), Phomopsis sp., and Botrytis cinerea (B. cinerea). Bioassay results demonstrated that some of the target compounds exhibited moderate to good in vitro antibacterial and antifungal activities. In particular, compound 4e revealed excellent in vitro antibacterial activity against Xoo, Xoc, and Xac, and its EC50 values of 15, 19, and 23 μg/mL, respectively, were superior to those of Bismerthiazol and Thiodiazole copper. Meanwhile, compound 3b revealed moderate in vitro antifungal activity against B. dothidea at 50 μg/mL, and the inhibition rate reached 88%, which was even better than that of Pyrimethanil, however, lower than that of Carbendazim. To the best of our knowledge, this is the first report on the antibacterial and antifungal activities of this series of novel thiochromanone derivatives containing a carboxamide moiety.

Bacterial leaf streak 1 encoding a mitogen-activated protein kinase confers resistance to bacterial leaf streak in rice.

Bacterial leaf streak (BLS) is a major bacterial disease of rice. Utilization of host genetic resistance has become one of the most important strategies for controlling BLS. However, only a few resistance genes have been characterized. Previously, a recessive BLS resistance gene bls1 was roughly mapped on chromosome 6. Here, we further delineated bls1 to a 21kb region spanning four genes. Genetic analysis confirmed that the gene encoding a mitogen-activated protein kinase (OsMAPK6) is the target of the allelic genes BLS1 and bls1. Overexpression of BLS1 weakened resistance to the specific Xanthomonas oryzae pv. oryzicola (Xoc) strain JZ-8, while low expression of bls1 increased resistance. However, both overexpression of BLS1 and low expression of bls1 could increase no-race-specific broad-spectrum resistance. These results indicate that BLS1 and bls1 negatively regulate race-specific resistance to Xoc strain JZ-8 but positively and negatively control broad-spectrum resistance, respectively. Subcellular localization demonstrated that OsMAPK6 was localized in the nucleus. RGA4, which is known to mediate resistance to Xoc, is the potential target of OsMAPK6. Overexpression of BLS1 and low expression of bls1 showed increase in salicylic acid and induced expression of defense-related genes, simultaneously increasing broad-spectrum resistance. Moreover, low expression of bls1 showed increase an in jasmonic acid and abscisic acid, in company with an increase in resistance to Xoc strain JZ-8. Collectively, our study provides new insights into the understanding of BLS resistance and facilitates the development of rice host-resistant cultivars.

Design, synthesis, and bioactivity evaluation of novel thiochromanone derivatives containing an oxime or oxime ether moiety

AbstractIn this study, using botanical active component thiochromanone as the lead compound, a series of novel thiochromanone derivatives containing an oxime or oxime ether moiety were designed and synthesized. The half‐maximal effective concentration (EC50) values of compound 4a against Xanthomonas oryzae pv. oryzae (Xoo), Xanthomonas oryzae pv. oryzicolaby (Xoc), and Xanthomonas axonopodis pv. citri (Xac) were 6, 10, and 15 μg/ml, respectively, which were superior to those of Bismerthiazol and Thiodiazole‐copper. Meanwhile, compound 4a also revealed better antifungal activity against Botrytis cinerea, with the EC50 value of 18 μg/ml, than that of Carbendazim. To the best of our knowledge, this is the first report on the antibacterial and antifungal activities of this series of novel thiochromanone derivatives containing an oxime or oxime ether moiety.

Synthesis, antibacterial activity and mechanism of new butenolides derivatives containing an amide moiety

A series of novel butenolide derivatives containing an amide were designed and synthesized with flupyradifurone as the lead compound. The biological activities test found that this series of compounds did not exhibit insecticidal activity, but had good antibacterial activities. Among all target compounds, compound 19 showed good antibacterial activity in vitro against Xanthomonas oryzae pv. oryzae (Xoo), with an EC50 value of 35.8 mg/L, which was superior to that of bismerthiazol (73.5 mg/L). Under greenhouse conditions, the curative and protective activities of compound 19 against bacterial leaf blight were 40.9% and 48.9% at 100 mg/L, respectively, which were superior to those of bismerthiazol (31.2% and 31.4%). In addition, compound 19 can not only cause changes in the cell surface morphology of Xoo, but also increase the activity of rice defense enzymes. The mechanism of action studies showed that the protective activity of compound 19 against rice bacterial leaf blight is closely related to the improvement of defense-related enzyme activities and the upregulation of proteins involved in oxidative phosphorylation.

Dysregulation of ClpP by Small-Molecule Activators Used Against Xanthomonas oryzae pv. oryzae Infections.

Rice bacterial leaf blight caused by Xanthomonas oryzae pv. oryzae (Xoo) is considered a destructive plant bacterial disease. The looming crisis of antibiotic resistance necessitates the discovery of antibiotics with new modes of action. Activated caseinolytic protease P (ClpP) can degrade bacterial FtsZ proteins that are essential for cell division; thus, we hypothesized that small-molecule-induced dysregulation of XooClpP may result in degradation of XooFtsZ to treat leaf blight diseases. In this work, we have determined the crystal structures of XooClpP, and its mutant bound with ADEP4, which revealed the action modes of XooClpP assemblies and XooFtsZ degradation by dysregulated XooClpP in the presence of small-molecule activators, such as ONC212 and ADEP4. Additionally, an antibacterial assessment demonstrated that ONC212 displays excellent activity against Xoo and prevents rice bacterial leaf blight in vivo. Thus, these unique antibacterial effects of small-molecule activators of XooClpP represent a potential strategy for the development of agricultural antibiotics by targeting bacterial ClpP.

Design, Synthesis and Antibacterial Activity of Novel Pyrimidine-Containing 4H-Chromen-4-One Derivatives*.

A series of pyrimidine-containing 4H-chromen-4-one derivatives were designed and synthesized by combining bioactive substructures. Preliminary biological activity results showed that most of the compounds displayed significant inhibitory activities in vitro against Xanthomonas axonopodis pv. Citri (X. axonopodis), Xanthomonas oryzae pv. oryzae (X. oryzae) and Ralstonia solanacearum (R. solanacearum). In particular, compound 2-[(3-{[5,7-dimethoxy-4-oxo-2-(3,4,5-trimethoxyphenyl)-4H-1-benzopyran-3-yl]oxy}propyl)sulfanyl]-4-(4-methylphenyl)-6-oxo-1,6-dihydropyrimidine-5-carbonitrile (4c) demonstrated a good inhibitory effect against X. axonopodis and X. oryzae, with the half-maximal effective concentration (EC50 ) values of 15.5 and 14.9 μg/mL, respectively, and compound 2-[(3-{[5,7-Dimethoxy-4-oxo-2-(3,4,5-trimethoxyphenyl)-4H-1-benzopyran-3-yl]oxy}propyl)sulfanyl]-4-(3-fluorophenyl)-6-oxo-1,6-dihydropyrimidine-5-carbonitrile (4h) showed the best antibacterial activity against R. solanacearum with an EC50 value of 14.7 μg/mL. These results were better than commercial reagents bismerthiazol (BT, 51.7, 70.1 and 52.7 μg/mL, respectively) and thiodiazole copper (TC, 77.9, 95.8 and 72.1 μg/mL, respectively). In vivo antibacterial activity results indicated that compound 4c displayed better curative (42.4 %) and protective (49.2 %) activities for rice bacterial leaf blight than BT (35.2, 39.1 %) and TC (30.8, 27.3 %). The mechanism of compound 4c against X. oryzae was analyzed through scanning electron microscopy (SEM). These results indicated that pyrimidine-containing 4H-chromen-4-one derivatives have important value in the research of new agrochemicals.

Control of bacterial leaf blight disease in several varieties of rice plants (Oryza sativa L.) by using bacteria of Paenibacilus polymyxa Mace

Bacterial Leaf Blight Disease caused by bacteria Xanthomonas oryzae pv. Oryzae is an endemic disease found in all rice plantation in Indonesia. The bacteria infects plants from the vegetative to generative phase and is able to reduce production by up to 30%. Most of farmers control the disease by using chemical pesticides that cause pollution to the environment. While this study offers control by using biological pesticides with the bacteria Paenibacilus polymyxa Mace. The research aims to control Bacterial Leaf Blight Disease using P. polymyxa Mace in several varieties of rice plants (Oryza sativa L.) as well as to obtain effective concentrations of P. polymyxa Mace Bio agent to control Bacterial Leaf Blight Disease. Experiments were conducted using Split-plot design with 3 (three) replication. The main plot was the Concentration of P. Polymyxa Mace consist of 4 levels, they were P0=Control/Untreated, P1=2.5 mL.L-1 water, P2=5 mL.L-1 water, P3=7.5 mL.L-1 water, and as a Sub Plot was a Variety (V) consist of 3 levels, they were V1=Cibogo Variety, V2=Mekongga Variety, V3=Ciherang Variety. The results showed that that the Mekongga variety is the most resistant variety to the pathogen Xanthomonas oryzae pv. Oryzae. The use of P. Polymyxa Mace as biological agents effective to control Bacterial Leaf Blight caused by the pathogen X oryzae pv. Oryzae on several rice plant varieties (Oryza sativa L.), and the best concentration of P. Polymyxa Mace to control Bacterial Leaf Blight disease was 5 mL.L-1 water.

Identification of quantitative trait loci associated with resistance to Xanthomonas oryzae pv. oryzae pathotypes prevalent in South China

Bacterial blight (BB), which is caused by Xanthomonas oryzae pv. oryzae (Xoo), is an important rice disease responsible for significant yield losses. In the rice-growing regions of South China where BB outbreaks are common, the resistance of cultivars with BB resistance genes Xa4 and Xa21 has been lost because of rapid changes in the Xoo population structure and virulence. In this study, 421 diverse rice accessions were evaluated regarding their resistance to two Xoo strains, namely GD1358 (C5) and IV, which are prevalent pathotypes in South China and overcame the resistance of Xa4 and Xa21, respectively. Using the 4.8mio filtered SNP dataset, we conducted a genome-wide association study, which identified 13 loci associated with BB resistance, including eight new quantitative trait loci (QTL) and five QTL harboring known BB resistance genes: Xa3/Xa26, xa5, Xa35(t), Xa36(t), Xa40, Xa43(t), and xa44(t). Intriguingly, a steep peak was detected on chromosomes 5 and 11. Six QTL including three new ones, were distributed on chromosome 11, whereas a new QTL qBB5.1 and a known QTL were detected on chromosome 5. Haplotype analyses indicated that the LOC_Os05g01610 (OsPRAF2) gene within the qBB5.1 region, which encodes a PRAF protein, is associated with BB resistance. Furthermore, OsPRAF2 knockout lines generated using the CRISPR-Cpf1 system were significantly more resistant to Xoo strains than the wild-type plants. Our results provide researchers and breeders with useful information regarding QTL and gene resources, which may be relevant for developing new BB-resistant rice cultivars.

Efikasi Ekstrak Sirih, Rimpang Lengkuas dan Kunyit terhadap Penekanan Pertumbuhan Xanthomonas oryzae

One of the important diseases in rice is the Bacterial Leaf Blight (HDB) or the so-called kresek disease caused by Xanthomonas oryzae pv. oryzae. This disease is one of the main diseases of rice in Indonesia. This is supported by agricultural conditions in hot and humid tropical areas so that disease development is more optimal. The purpose of this study was to determine the efficacy of betel leaf extract and some rhizomes in suppressing the growth of Xanthomonas oryzae pv. oryzae in-vitro scale. The research was conducted at the Center for Forecasting Plant Pest Organisms (BBPOPT), Karawang, West Java. The extracts of galangal, turmeric, and betel were prepared at concentrations of 10, 15, and 25%, the method used was a scatter plate by taking 10, 50, and 100 μL of Xoo isolate liquid, holding the petri dish to a bunsen fire, and spraying Xoo isolates liquid. into a petri dish containing PSA media + rhizome extract, the dispersing tool used is drigalski. The results of daily observations of rhizome extract antagonist testing on Xoo growth showed that the treatment of betel leaf extract with a concentration of 10%, 15%, and 25% had a high bacterial inhibitory value compared to other treatments with 100% inhibition, whereas in the control treatment (only PSA media) shows that it does not have bacterial inhibition, and the galangal rhizome extract treatment has the highest inhibitory power when compared to other treatments on 100 μL of Xoo bacterial suppression.

Genome-Wide Association Mapping and Gene Expression Analysis Reveal the Negative Role of OsMYB21 in Regulating Bacterial Blight Resistance in Rice

BackgroundBacterial blight (BB), caused by Xanthomonas oryzae pv. oryzae (Xoo), is one of the most devastating diseases in rice all over the world. Due to the diversity and rapid evolution of Xoo, identification and use of the non-race specific quantitative resistance QTLs has been considered the preferred strategy for effective control of this disease. Although numerous QTLs for BB resistance have been identified, they haven’t been effectively used for improvement of BB resistance in rice due to their small effects and lack of knowledge on the function of genes underlying the QTLs.ResultsIn the present study, a genome-wide association study of BB resistance was performed in a rice core collection from South China. A total of 17 QTLs were identified to be associated with BB resistance. Among them, 13 QTLs were newly identified in the present study and the other 4 QTLs were co-localized with the previously reported QTLs or Xa genes that confer qualitative resistance to Xoo strains. Particularly, the qBBR11–4 on chromosome 11 explained the largest phenotypic variation in this study and was co-localized with the previously identified QTLs for BB and bacterial leaf streak (BLS) resistance against diverse strains in three studies, suggesting its broad-spectrum resistance and potential value in rice breeding. Through combined analysis of differential expression and annotations of the predicted genes within qBBR11–4 between two sets of rice accessions selected based on haplotypes and disease phenotypes, we identified the transcription factor OsMYB21 as the candidate gene for qBBR11–4. The OsMYB21 overexpressing plants exhibited decreased resistance to bacterial blight, accompanied with down-regulation of several defense-related genes compared with the wild-type plants.ConclusionThe results suggest that OsMYB21 negatively regulates bacterial blight resistance in rice, and this gene can be a promising target in rice breeding by using the gene editing method. In addition, the potential candidate genes for the 13 novel QTLs for BB resistance were also analyzed in this study, providing a new source for cloning of genes associated with BB resistance and molecular breeding in rice.

Proteomic and Transcriptomic Analyses Provide Novel Insights into the Crucial Roles of Host-Induced Carbohydrate Metabolism Enzymes in Xanthomonas oryzae pv. oryzae Virulence and Rice-Xoo Interaction

BackgroundXanthomonas oryzae pv. oryzae (Xoo) causes bacterial leaf blight, a devastating rice disease. The Xoo-rice interaction, wherein wide ranging host- and pathogen-derived proteins and genes wage molecular arms race, is a research hotspot. Hence, the identification of novel rice-induced Xoo virulence factors and characterization of their roles affecting rice global gene expression profiles will provide an integrated and better understanding of Xoo-rice interactions from the molecular perspective.ResultsUsing comparative proteomics and an in vitro interaction system, we revealed that 5 protein spots from Xoo exhibited significantly different expression patterns (|fold change| > 1.5) at 3, 6, 12 h after susceptible rice leaf extract (RLX) treatment. MALDI-TOF MS analysis and pathogenicity tests showed that 4 host-induced proteins, including phosphohexose mutase, inositol monophosphatase, arginase and septum site-determining protein, affected Xoo virulence. Among them, mutants of two host-induced carbohydrate metabolism enzyme-encoding genes, ΔxanA and Δimp, elicited enhanced defense responses and nearly abolished Xoo virulence in rice. To decipher rice differentially expressed genes (DEGs) associated with xanA and imp, transcriptomic responses of ΔxanA-treated and Δimp-treated susceptible rice were compared to those in rice treated with PXO99A at 1 and 3 dpi. A total of 1521 and 227 DEGs were identified for PXO99A vs Δimp at 1 and 3 dpi, while for PXO99A vs ΔxanA, there were 131 and 106 DEGs, respectively. GO, KEGG and MapMan analyses revealed that the DEGs for PXO99A vs Δimp were mainly involved in photosynthesis, signal transduction, transcription, oxidation-reduction, hydrogen peroxide catabolism, ion transport, phenylpropanoid biosynthesis and metabolism of carbohydrates, lipids, amino acids, secondary metabolites, hormones, and nucleotides, while the DEGs from PXO99A vs ΔxanA were predominantly associated with photosynthesis, signal transduction, oxidation-reduction, phenylpropanoid biosynthesis, cytochrome P450 and metabolism of carbohydrates, lipids, amino acids, secondary metabolites and hormones. Although most pathways were associated with both the Δimp and ΔxanA treatments, the underlying genes were not the same.ConclusionOur study identified two novel host-induced virulence factors XanA and Imp in Xoo, and revealed their roles in global gene expression in susceptible rice. These results provide valuable insights into the molecular mechanisms of pathogen infection strategies and plant immunity.

Ginger Essential Oils-Loaded Nanoemulsions: Potential Strategy to Manage Bacterial Leaf Blight Disease and Enhanced Rice Yield.

The bacterial leaf blight (BLB) caused by Xanthomonas oryzae pv. oryzae (Xoo) is one of the most serious rice diseases, causing huge yield losses worldwide. Several technologies and approaches have been opted to reduce the damage; however, these have had limited success. Recently, scientists have been focusing their efforts on developing efficient and environmentally friendly nanobactericides for controlling bacterial diseases in rice fields. In the present study, a scanning electron microscope (SEM), transmission electron microscope (TEM), and a confocal laser scanning microscope (CLSM) were utilized to investigate the mode of actions of ginger EOs on the cell structure of Xoo. The ginger EOs caused the cells to grow abnormally, resulting in an irregular form with hollow layers, whereas the dimethylsulfoxide (DMSO) treatment showed a typical rod shape for the Xoo cell. Ginger EOs restricted the growth and production of biofilms by reducing the number of biofilms generated as indicated by CLSM. Due to the instability, poor solubility, and durability of ginger EOs, a nanoemulsions approach was used, and a glasshouse trial was performed to assess their efficacy on BLB disease control. The in vitro antibacterial activity of the developed nanobactericides was promising at different concentration (50–125 µL/mL) tested. The efficacy was concentration-dependent. There was significant antibacterial activity recorded at higher concentrations. A glasshouse trial revealed that developed nanobactericides managed to suppress BLB disease severity effectively. Treatment at a concentration of 125 μL/mL was the best based on the suppression of disease severity index, AUDPC value, disease reduction (DR), and protection index (PI). Furthermore, findings on plant growth, physiological features, and yield parameters were significantly enhanced compared to the positive control treatment. In conclusion, the results indicated that ginger essential oils loaded-nanoemulsions are a promising alternative to synthetic antibiotics in suppressing Xoo growth, regulating the BLB disease, and enhancing rice yield under a glasshouse trial.

Bioactive indole alkaloids from insect derived endophytic Aspergillus lentulus

As part of our program to discover new bioactive agents from endophytic fungi, three new indole alkaloids (1–2, 4) along with twelve known compounds were isolated from an inset derived endophytic strain Aspergillus lentulus. Their structures were determined by comprehensive spectroscopic analyses of 1D/2D NMR and HR-ESI-MS data. The absolute configurations were confirmed by ECD calculation using Time-dependent Density functional theory (TD-DFT) at the B3LYP/6–31 + g (d, p) level and Rh2(OCOCF3)4-induced ECD experiments. Compounds 2, 4, 5, 13 and 15 exhibited moderate cytotoxic effects on A549 cell line with IC50 in the range of 17.92–48.29 μM. Compounds 1, 2 and 13–15 displayed the anti-bacterial activity against Xanthomonas oryzae pv. oryzae and Xanthomonas oryzae pv. oryzicola with MIC values ranging from 25 to 100 μg/mL.

Antimicrobial activity of methanolic extracts of Vernonia cinerea against Xanthomonas oryzae and identification of their compounds using in silico techniques.

Bacterial Leaf Blight (BLB) disease is an extremely ruinous disease in rice, caused by Xanthomonas oryzae pv. oryzae (Xoo). Although various chemicals are available to manage BLB, they are toxic to the environment as well as humans. Hence there is a need to develop new pesticides as alternatives to hazardous chemicals. Therefore, a study was carried out to discover new potent natural pesticides against Xoo from different solvent extracts of Vernonia cinerea. Among all the fractions, the methanolic extract showed the highest inhibition zone. Further, to gain mechanistic insight of inhibitory action, 40 molecules of methanolic extracts were subjected for in silico study against two enzymes D-alanine—D-alanine ligase (Ddl) and Peptide deformylase (PDF). In silico study showed Rutin and Methanone, [1,4-dimethyl-7-(1- methylethyl)-2- azulenyl]phenyl have a good binding affinity with Ddl while Phenol, 2,4-bis(1-phenylethyl)- and 1,2-Benzenedicarboxylic acid, diisooctyl ester showed an excellent binding affinity to PDF. Finally, the system biology approach was applied to understand the agrochemical’s effect in the cell system of bacteria against both the enzymes. Conclusively, these four-hit compounds may have strong potential against Xoo and can be used as biopesticides in the future.

Flavonone 3-hydroxylase Relieves Bacterial Leaf Blight Stress in Rice via Overaccumulation of Antioxidant Flavonoids and Induction of Defense Genes and Hormones.

Efficient accumulation of flavonoids is important for increased tolerance to biotic stress. Although several plant defense mechanisms are known, the roles of many pathways, proteins, and secondary metabolites in stress tolerance are unknown. We generated a flavanone 3-hydroxylase (F3H) overexpressor rice line and inoculated Xanthomonas Oryzae pv. oryzae and compared the control and wildtype inoculated plants. In addition to promoting plant growth and developmental maintenance, the overexpression of F3H increased the accumulation of flavonoids and increased tolerance to bacterial leaf blight (BLB) stress. Moreover, leaf lesion length was higher in the infected wildtype plants compared with infected transgenics. Kaempferol and quercetin, which scavenge reactive oxygen species, overaccumulated in transgenic lines compared with wildtypes in response to pathogenic infection, detected by scanning electron microscopy and spectrophotometry. The induction of F3H altered the antioxidant system and reduced the levels of glutathione peroxidase activity and malondialdehyde (MDA) contents in the transgenic lines compared with the wildtypes. Downstream gene regulation analysis showed that the expression of F3H increased the regulation of flavonol synthase (FLS), dihydroflavonol 4-reductase (DFR), and slender rice mutant (SLR1) during BLB stress. The analysis of SA and JA signaling revealed an antagonistic interaction between both hormones and that F3H induction significantly promoted SA and inhibited JA accumulation in the transgenic lines. SA-dependent nonexpressor pathogenesis-related (NPR1) and Xa1 showed significant upregulation in the infected transgenic lines compared with the infected control and wildtype lines. Thus, the overexpression of F3H was essential for increasing BLB stress tolerance.

Rice Stomatal Mega-Papillae Restrict Water Loss and Pathogen Entry.

Rice (Oryza sativa) is a water-intensive crop, and like other plants uses stomata to balance CO2 uptake with water-loss. To identify agronomic traits related to rice stomatal complexes, an anatomical screen of 64 Thai and 100 global rice cultivars was undertaken. Epidermal outgrowths called papillae were identified on the stomatal subsidiary cells of all cultivars. These were also detected on eight other species of the Oryza genus but not on the stomata of any other plant species we surveyed. Our rice screen identified two cultivars that had “mega-papillae” that were so large or abundant that their stomatal pores were partially occluded; Kalubala Vee had extra-large papillae, and Dharia had approximately twice the normal number of papillae. These were most accentuated on the flag leaves, but mega-papillae were also detectable on earlier forming leaves. Energy dispersive X-Ray spectrometry revealed that silicon is the major component of stomatal papillae. We studied the potential function(s) of mega-papillae by assessing gas exchange and pathogen infection rates. Under saturating light conditions, mega-papillae bearing cultivars had reduced stomatal conductance and their stomata were slower to close and re-open, but photosynthetic assimilation was not significantly affected. Assessment of an F3 hybrid population treated with Xanthomonas oryzae pv. oryzicola indicated that subsidiary cell mega-papillae may aid in preventing bacterial leaf streak infection. Our results highlight stomatal mega-papillae as a novel rice trait that influences gas exchange, stomatal dynamics, and defense against stomatal pathogens which we propose could benefit the performance of future rice crops.