Phaseolotoxin: Environmental Conditions and Regulatory Mechanisms Involved in Its Synthesis.

Phaseolotoxin is an antimetabolite toxin produced by diverse pathovars of Pseudomonas syringae which affects various plants, causing diseases of economic importance. Phaseolotoxin contributes to the systemic dissemination of the pathogen in the plant, therefore it is recognized as a major virulence factor. Genetic traits such as the Pht cluster, appear defining to the toxigenic strains phaseolotoxin producers. Extensive research has contributed to our knowledge concerning the regulation of phaseolotoxin revealing a complex regulatory network that involves processes at the transcriptional and posttranscriptional levels, in which specific and global regulators participate. Even more, significant advances in understanding how specific signals, including host metabolites, nutrient sources, and physical parameters such as the temperature, can affect phaseolotoxin production have been made. A general overview of the phaseolotoxin regulation, focusing on the chemical and physical cues, and regulatory pathways involved in the expression of this major virulence factor will be given in the present work.

Nitric Oxide Mitigates the Deleterious Effects Caused by Infection of Pseudomonas syringae pv. syringae and Modulates the Carbon Assimilation Process in Sweet Cherry under Water Stress.

Bacterial canker is an important disease of sweet cherry plants mainly caused by Pseudomonas syringae pv. syringae (Pss). Water deficit profoundly impairs the yield of this crop. Nitric oxide (NO) is a molecule that plays an important role in the plant defense mechanisms. To evaluate the protection exerted by NO against Pss infection under normal or water-restricted conditions, sodium nitroprusside (SNP), a NO donor, was applied to sweet cherry plants cv. Lapins, before they were exposed to Pss infection under normal or water-restricted conditions throughout two seasons. Well-watered plants treated with exogenous NO presented a lower susceptibility to Pss. A lower susceptibility to Pss was also induced in plants by water stress and this effect was increased when water stress was accompanied by exogenous NO. The lower susceptibility to Pss induced either by exogenous NO or water stress was accompanied by a decrease in the internal bacterial population. In well-watered plants, exogenous NO increased the stomatal conductance and the net CO2 assimilation. In water-stressed plants, NO induced an increase in the leaf membranes stability and proline content, but not an increase in the CO2 assimilation or the stomatal conductance.

Molecular Characterization and Genome Mechanical Features of Two Newly Isolated Polyvalent Bacteriophages Infecting Pseudomonas syringae pv. garcae.

Coffee plants have been targeted by a devastating bacterial disease, a condition known as bacterial blight, caused by the phytopathogen Pseudomonas syringae pv. garcae (Psg). Conventional treatments of coffee plantations affected by the disease involve frequent spraying with copper- and kasugamycin-derived compounds, but they are both highly toxic to the environment and stimulate the appearance of bacterial resistance. Herein, we report the molecular characterization and mechanical features of the genome of two newly isolated (putative polyvalent) lytic phages for Psg. The isolated phages belong to class Caudoviricetes and present a myovirus-like morphotype belonging to the genuses Tequatrovirus (PsgM02F) and Phapecoctavirus (PsgM04F) of the subfamilies Straboviridae (PsgM02F) and Stephanstirmvirinae (PsgM04F), according to recent bacterial viruses' taxonomy, based on their complete genome sequences. The 165,282 bp (PsgM02F) and 151,205 bp (PsgM04F) genomes do not feature any lysogenic-related (integrase) genes and, hence, can safely be assumed to follow a lytic lifestyle. While phage PsgM02F produced a morphogenesis yield of 124 virions per host cell, phage PsgM04F produced only 12 virions per host cell, indicating that they replicate well in Psg with a 50 min latency period. Genome mechanical analyses established a relationship between genome bendability and virion morphogenesis yield within infected host cells.

Genetic and phenotypical diversity of Pseudomonas syringae population in the Russian Federation / Diversidade genética e fenotípica da população de Pseudomonas syringae na Federação Russa

Proteobacteria comprising species of Pseudomonas syringae group cause diseases of many plants around the world. The phytopathogen has a complex taxonomic structure, which is constantly being revised due to the emergence of new molecular and biochemical diagnostic methods. Here for the first time, we describe the genetic and phenotypic diversity of 57 strains of Pseudomonas syringae isolated from affected soybeans, cereals, sunflowers, and other plants in the Russian Federation from 1950 to 2019. Genetic diversity was assessed by Multi Locus Sequence Analysis (MLSA) using fragments of the genes of glyceraldehyde-3-phosphate dehydrogenase (gapdh), the DNA-directed RNA polymerase subunit D (rpoD), gyrase (topoisomerase) B subunit (gyrB), and citrate synthase I (gltA). The synthesis of syringomycin and coronatine by bacteria was assessed by the reaction of susceptible yeast culture, seedlings of barley, tomato, and sunflower, and by presence of toxin genes confirmed by PCR test. The pathogenicity of the strains was confirmed on seedlings of dicotyledonous and monocotyledonous plants of peas, soybean, sunflowers, barley and wheat, as the most affected crops. The sensitivity of bacteria to 10 antibiotics of the main mechanisms of activity and two bactericidal commercial products was tested by standard disc method. The obtained results showed a high genetic homogeneity of the Russian population of P. syringae, which infects various agricultural crops, and an increase in the proportion of antibiotic-resistant strains over the years.

Proteobactérias compreendendo espécies do grupo Pseudomonas syringae causam doenças de muitas plantas ao redor do mundo. O fitopatógeno possui uma estrutura taxonômica complexa, que está em constante revisão devido ao surgimento de novos métodos de diagnóstico molecular e bioquímico. Aqui, pela primeira vez, descrevemos a diversidade genética e fenotípica de 57 cepas de Pseudomonas syringae isoladas de soja, cereais, girassol e outras plantas afetadas na Federação Russa de 1950 a 2019. A diversidade genética foi avaliada por análise de sequência multilocus (MLSA) usando fragmentos dos genes da gliceraldeído-3-fosfato desidrogenase (gapdh), a subunidade D da RNA polimerase dirigida por DNA (rpoD), a subunidade B da girase (topoisomerase) (gyrB) e a citrato sintase I (gltA). A síntese de siringomicina e coronatina por bactérias foi avaliada pela reação de cultura de leveduras suscetíveis, plântulas de cevada, tomate e girassol, e pela presença de genes de toxina confirmados pelo teste de PCR. A patogenicidade das cepas foi confirmada em mudas de plantas dicotiledôneas e monocotiledôneas de ervilha, soja, girassol, cevada e trigo, como as culturas mais afetadas. A sensibilidade das bactérias a 10 antibióticos dos principais mecanismos de atividade e dois produtos bactericidas comerciais foi testada pelo método de disco padrão. Os resultados obtidos mostraram uma alta homogeneidade genética da população russa de P. syringae, que infecta várias culturas agrícolas, e um aumento na proporção de cepas resistentes a antibióticos ao longo dos anos.

Development of a Genome-Informed Protocol for Detection of Pseudomonas amygdali pv. morsprunorum Using LAMP and PCR.

One of the causal agents of bacterial canker is Pseudomonas amygdali pv. morsprunorum-Pam (formerly Pseudomonas syringae pv. morsprunorum). Recently detected in Chile, Pam is known to cause lesions in the aerial parts of the plant, followed by more severe symptoms such as cankers and gummosis in the later stages of the disease. This study presents the design of PCR and LAMP detection methods for the specific and sensitive identification of Pseudomonas amygdali pv. morsprunorum (Pam) from cherry trees. Twelve Pseudomonas isolates were collected, sequenced, and later characterized by Multi-locus Sequence Analysis (MLSA) and Average Nucleotide Identity by blast (ANIb). Three of them (11116B2, S1 Pam, and S2 Pam) were identified as Pseudomonas amygdali pv. morsprunorum and were used to find specific genes through RAST server, by comparing their genome with that of other Pseudomonas, including isolates from other Pam strains. The effector gene HopAU1 was selected for the design of primers to be used for both techniques, evaluating sensitivity and specificity, and the ability to detect Pam directly from plant tissues. While the PCR detection limit was 100 pg of purified bacterial DNA per reaction, the LAMP assays were able to detect up to 1 fg of purified DNA per reaction. Similar results were observed using plant tissues, LAMP being more sensitive than PCR, including when using DNA extracted from infected plant tissues. Both detection methods were tested in the presence of 30 other bacterial genera, with LAMP being more sensitive than PCR.

Newly isolated phages preying on Pseudomonas syringae pv. garcae: In vitro and ex vivo inactivation studies in coffee plant leafs.

Coffee canker, or bacterial halo blight (BHB) of coffee, is a disease caused by the phytopathogenic bacterium Pseudomonas syringae pv. garcae (Psg), having been found for the first time in 1955, in the Garça region (State of São Paulo), and which has stood out in the Brazilian coffee plantations in recent years, leading to severe economic losses that seriously affect coffee trade. The treatments available are still scarce, involving frequent spraying of coffee plantations with either copper derivatives or the antibiotic kasugamycin. However, these compounds should be avoided due to environmental toxicity and the development of bacterial resistances. Herein we report the isolation and physical/biological characterisation of two novel lytic phages and their efficacy in the control of Psg. Phages ph002F and ph004F were isolated from coffee plant leaves in Brazil (Sorocaba/SP and Itu/SP cities), using Psg IBSBF-158 as the host. According to the transmission electron microscopy analyses, both phages belong to the class Caudoviricetes and present myovirus-like morphotypes. Phages ph002F and ph004F showed eclipse times of 5 min and 20 min, respectively, and a burst size of 123 PFU/host cell and 12 PFU/host cell, respectively, allowing to conclude they replicate well in Psg IBSBF-158 with latency periods of 50 min. Phage ph002F (reduction of 4.59 log CFU/mL, compared to uninfected culture) was more effective in inactivating Psg than phage ph004F (reduction of 3.85 log CFU/mL) after 10 h of incubation at a MOI of 10. As a cocktail, the two phages were highly effective in reducing the bacterial load (reduction of 5.26 log CFU/mL at a MOI of 0.1 or reduction of 5.03 log CFU/mL at a MOI of 10, relative to untreated culture), after 12 h of treatment. This study provides evidence that the isolated phages are promising candidates against the causative agent of BHB in coffee plants.

Expression of EPL1 from Trichoderma atroviride in Arabidopsis Confers Resistance to Bacterial and Fungal Pathogens.

During plant interaction with beneficial microorganisms, fungi secrete a battery of elicitors that trigger plant defenses against pathogenic microorganisms. Among the elicitor molecules secreted by Trichoderma are cerato-platanin proteins, such as EPL1, from Trichoderma atroviride. In this study, Arabidopsis thaliana plants that express the TaEPL1 gene were challenged with phytopathogens to evaluate whether expression of EPL1 confers increased resistance to the bacterial pathogen Pseudomonas syringae and the necrotrophic fungus Botrytis cinerea. Infection assays showed that Arabidopsis EPL1-2, EPL1-3, EPL1-4 expressing lines were more resistant to both pathogens in comparison to WT plants. After Pseudomonas syringae infection, there were reduced disease symptoms (e.g., small chlorotic spots) and low bacterial titers in the three 35S::TaEPL1 expression lines. Similarly; 35S::TaEPL1 expression lines were more resistant to Botrytis cinerea infection, showing smaller lesion size in comparison to WT. Interestingly, an increase in ROS levels was detected in 35S::TaEPL1 expression lines when compared to WT. A higher expression of SA- and JA-response genes occurred in the 35S::TaEPL1 lines, which could explain the resistance of these EPL1 expression lines to both pathogens. We propose that EPL1 is an excellent elicitor, which can be used to generate crops with improved resistance to broad-spectrum diseases.

Loss-of-function mutations in WRKY22 and WRKY25 impair stomatal-mediated immunity and PTI and ETI responses against Pseudomonas syringae pv. tomato.

Plants defend themselves against pathogens using a two-layered immune system. The first response, pattern-triggered immunity (PTI), is activated upon recognition of microbe-associated molecular patterns (MAMPs). Virulent bacteria such as Pseudomonas syringae pv. tomato (Pst), deliver effector proteins into the plant cell to promote susceptibility. However, some plants possess resistance (R) proteins that recognize specific effectors leading to the activation of the second response, effector-triggered immunity (ETI). Resistant tomatoes such as Río Grande-PtoR recognize two Pst effectors (AvrPto and AvrPtoB) through the host Pto/Prf complex and activate ETI. We previously showed that the transcription factors (TF) WRKY22 and WRKY25 are positive regulators of plant immunity against bacterial and potentially non-bacterial pathogens in Nicotiana benthamiana. Here, the CRISPR-Cas9 technique was used to develop three knockout tomato lines for either one or both TFs. The single and double mutants were all compromised in Pto/Prf-mediated ETI and had a weaker PTI response. The stomata apertures in all of the mutant lines did not respond to darkness or challenge with Pst DC3000. The WRKY22 and WRKY25 proteins both localize in the nucleus, but we found no evidence of a physical interaction between them. The WRKY22 TF was found to be involved in the transcriptional regulation of WRKY25, supporting the idea that they are not functionally redundant. Together, our results indicate that both WRKY TFs play a role in modulating stomata and are positive regulators of plant immunity in tomato.

Rootstock increases the physiological defence of tomato plants against Pseudomonas syringae pv. tomato infection.

Climate change has intensified the infection of tomato plants by pathogens such as Pseudomonas syringae pv. tomato (Pst). Rootstocks may increase plant tolerance to leaf phytopathogens. The aim of this study was to evaluate the effects of the tolerant Poncho Negro (R) tomato rootstock on physiological defence and the role of hydrogen sulfide (H2S) in susceptible Limachino (L) tomato plant responses to Pst attack. Ungrafted (L), self-grafted (L/L), and grafted (L/R) plants were infected with Pst. Rootstock increased the concentration of antioxidant compounds including ascorbate in the scion. Tolerant rootstock induced an increase of H2S in the scion, which correlated with enhanced expression of the SlAPX2 gene. A high accumulation of salicylic acid was observed in Pst-inoculated grafted L/L and L/R plants, but this was higher in L/R plants. The increase of H2S during Pst infection was associated with a reduction of ethylene in L/R plants. Our study indicates that the Poncho Negro rootstock reduced the symptoms of bacterial speck disease in the Limachino tomato plants, conferring tolerance to Pst infection. This study provides new knowledge about the impact of rootstock in the defence of tomato plants against leaf pathogens that could be used in sustainable management of tomato cultivation.

A Recipe for Success: Three Key Strategies Used by Aphids and Pseudomonas syringae to Colonize the Phyllosphere.

Aphids and Pseudomonas syringae are a permanent challenge for agriculture, causing severe losses to the crop industry worldwide. Despite the obvious phylogenetic distance between them, both have become predominant colonizers of the plant kingdom. In this study, we reviewed three key steps of spread and colonization that aphids and P. syringae have mastered to successfully colonize the phyllosphere. These steps involve (i) plant-to-plant movement for locating new nutritional sources, (ii) disruption and modification of the apoplast to facilitate nutrient acquisition, and (iii) suppression of host defenses through effector proteins. In addition, we will provide insights about the direct interaction between aphids and P. syringae and how this yet underrated phenomenon could bring new ecological implications for both organisms beyond their pathogenicity.

Xanthomonas natriuretic peptide is recognized by the Arabidopsis natriuretic peptide receptor 1 and through this interaction triggers similar plant responses to its plant counterpart.

Plant natriuretic peptides (PNPs) are hormone peptides that participate in the regulation of ions and water homeostasis in plants. Xanthomonas citri subsp. citri (Xcc) the causal agent of citrus canker disease also possesses a PNP-like peptide (XacPNP). This peptide, similarly to AtPNP-A, the most studied PNP from Arabidopsis thaliana, causes stomatal aperture and enhances photosynthetic efficiency in plant leaves. Thus, the function that has been attributed to XacPNP is to contribute to maintain photosynthetic efficiency and water homeostasis in plant tissue during the infection process, to create favorable conditions for biotrophic pathogens survival. A PNP receptor (AtPNP-R1) for AtPNP-A has been identified and the AtPNP-A activity in regulation of water homeostasis has been observed to depend on the presence of AtPNP-R1. Here, we demonstrated that both AtPNP-A and XacPNP require the presence of AtPNP-R1 to induce plant stomatal aperture. Also, less necrotic tissue was found in infections with pathogens expressing XacPNP and this was dependent on the presence of AtPNP-R1, suggesting that XacPNP interacts with this receptor to exert its function. Finally, we confirmed that AtPNP-A and XacPNP interact with AtPNP-R1 in planta, which support the idea that XacPNP triggers similar plant responses to its plant counterpart.

The TGA Transcription Factors from Clade II Negatively Regulate the Salicylic Acid Accumulation in Arabidopsis.

Salicylic acid (SA) is a hormone that modulates plant defenses by inducing changes in gene expression. The mechanisms that control SA accumulation are essential for understanding the defensive process. TGA transcription factors from clade II in Arabidopsis, which include the proteins TGA2, TGA5, and TGA6, are known to be key positive mediators for the transcription of genes such as PR-1 that are induced by SA application. However, unexpectedly, stress conditions that induce SA accumulation, such as infection with the avirulent pathogen P. syringae DC3000/AvrRPM1 and UV-C irradiation, result in enhanced PR-1 induction in plants lacking the clade II TGAs (tga256 plants). Increased PR-1 induction was accompanied by enhanced isochorismate synthase-dependent SA production as well as the upregulation of several genes involved in the hormone's accumulation. In response to avirulent P. syringae, PR-1 was previously shown to be controlled by both SA-dependent and -independent pathways. Therefore, the enhanced induction of PR-1 (and other defense genes) and accumulation of SA in the tga256 mutant plants is consistent with the clade II TGA factors providing negative feedback regulation of the SA-dependent and/or -independent pathways. Together, our results indicate that the TGA transcription factors from clade II negatively control SA accumulation under stress conditions that induce the hormone production. Our study describes a mechanism involving old actors playing new roles in regulating SA homeostasis under stress.

Inferring the Significance of the Polyamine Metabolism in the Phytopathogenic Bacteria Pseudomonas syringae: A Meta-Analysis Approach.

To succeed in plant invasion, phytopathogenic bacteria rely on virulence mechanisms to subvert plant immunity and create favorable conditions for growth. This process requires a precise regulation in the production of important proteins and metabolites. Among them, the family of compounds known as polyamines have attracted considerable attention as they are involved in important cellular processes, but it is not known yet how phytopathogenic bacteria regulate polyamine homeostasis in the plant environment. In the present study, we performed a meta-analysis of publicly available transcriptomic data from experiments conducted on bacteria to begin delving into this topic and better understand the regulation of polyamine metabolism and its links to pathogenicity. We focused our research on Pseudomonas syringae, an important phytopathogen that causes disease in many economically valuable plant species. Our analysis discovered that polyamine synthesis, as well as general gene expression activation and energy production are induced in the early stages of the disease. On the contrary, synthesis of these compounds is inhibited whereas its transport is upregulated later in the process, which correlates with the induction of virulence genes and the metabolism of nitrogen and carboxylic acids. We also found that activation of plant defense mechanisms affects bacterial polyamine synthesis to some extent, which could reduce bacterial cell fitness in the plant environment. Furthermore, data suggest that a proper bacterial response to oxidative conditions requires a decrease in polyamine production. The implications of these findings are discussed.

Molecular and Genomic Characterization of the Pseudomonas syringae Phylogroup 4: An Emerging Pathogen of Arabidopsis thaliana and Nicotiana benthamiana.

Environmental fluctuations such as increased temperature, water availability, and air CO2 concentration triggered by climate change influence plant disease dynamics by affecting hosts, pathogens, and their interactions. Here, we describe a newly discovered Pseudomonas syringae strain found in a natural population of Arabidopsis thaliana collected from the southwest of France. This strain, called Psy RAYR-BL, is highly virulent on natural Arabidopsis accessions, Arabidopsis model accession Columbia 0, and tobacco plants. Despite the severe disease phenotype caused by the Psy RAYR-BL strain, we identified a reduced repertoire of putative Type III virulence effectors by genomic sequencing compared to P. syringae pv tomato (Pst) DC3000. Furthermore, hopBJ1Psy is found exclusively on the Psy RAYR-BL genome but not in the Pst DC3000 genome. The plant expression of HopBJ1Psy induces ROS accumulation and cell death. In addition, HopBJ1Psy participates as a virulence factor in this plant-pathogen interaction, likely explaining the severity of the disease symptoms. This research describes the characterization of a newly discovered plant pathogen strain and possible virulence mechanisms underlying the infection process shaped by natural and changing environmental conditions.

Copper formulations in bacterial blight control and toxic effects on coffee seedlings

Bacterial blight of coffee (Pseudomonas syringae pv. garcae) is an important coffee disease and can be controlled using antibiotics and copper-based compounds. However, copper-based compounds raise doubts among coffee growers regarding bacterial blight control efficiency and phytotoxic potential. In this work, coffee plants were sprayed with different copper molecules in order to study their efficiency on bacterial blight control and the phytotoxic potential. Seven copper formulations, cuprous oxide, copper oxychloride, copper nitrate, copper hydroxide 1 (water-dispersible granules) and 2 (concentrated suspension), copper sulfate 1 (complexed with gluconic acid) and 2 (Bordeaux mixture) were studied. The copper formulations efficiency was compared with the antibiotic kasugamycin, saline solution, and control. In controlled environmental conditions of temperature, relative humidity, and photoperiod, coffee seedlings were sprayed with the treatments and after 24 hours they were inoculated with Pseudomonas syringae pv. garcae suspension. Disease incidence and severity assessments were performed in a 2-day interval during a 16-day period. Phytotoxicity incidence and severity, mapping, and quantification of copper on the leaf tissue surface, dried leaves weight, and total copper leaf content were assessed 16 days after pathogen inoculation. Data were submitted to the Scott-Knott test (p < 0.05). Cuprous oxide and copper sulfate 2 proved most efficient to bacterial blight control, causing lower phytotoxicity effect, best covering, and persistence on leaf tissues. Copper nitrate and copper sulfate complexed with gluconic acid were more phytotoxicity compared to other copper formulations.

First Report of bacterial speck caused by Pseudomonas syringae pv. tomato Race 1 affecting tomato in different Regions of Chile.

In Chile, tomato is one of the most widely cultivated vegetables, with around 5,000 ha for fresh market and 8,000 ha for processing industry. During recent years, symptoms of bacterial speck caused by Pseudomonas syringae pv. tomato, have been observed more frequently in tomato plants in different regions of Chile. This pathogen was first identified in Chile in 1987 (Latorre & Lolas, 1988) and the presence of an apparent new variant was reported in 2004 (Besoain et al. 2004). To characterize the pathogen that was affecting this crop, samples of diseased tomato plants were taken in three regions of Chile. The samples were collected in 2016 in Northern Chile in Lluta Valley from the Arica y Parinacota Region, and in Central Chile, in 2014 in Limache from Valparaíso Region and in 2015 in Pichidegua from O´Higgins Region. Affected tomato plants exhibited dark brown to black lesions surrounded by yellow halos in the leaves, and dark brown to black lesions in the stems, pedicels, and peduncles. Plants tissues were macerated, and the suspension was spread on King's B medium, resulting in fluorescent colonies visualized under 366 nm UV light. LOPAT tests results of three selected isolates from different Regions, were: levan production (+), oxidase reaction (-), potato soft rot (-), arginine dihydrolase production (-), and tobacco hypersensitivity (+) (Lelliot et al. 1966). Molecular identification was carried out by amplification and sequence analysis of housekeeping genes cts, encoding citrate synthase, gyrB, encoding DNA gyrase B, and rpoD, encoding sigma factor 70 (Hwang et al. 2005; Sarkar & Guttmann 2004) (GenBank Accessions No. OK001658-OK001666). BLAST analysis of cts and rpoD genes of the three isolates resulted in a match with a 100% identity (919 bp and 491 bp respectively) with Pseudomonas syringae pv. tomato strain B13-200 (GenBank: CP019871.1). BLAST analysis of gyrB gene of two isolates resulted in a match with a 100% identity (684 bp) and one isolate with 99.85% (683 bp) with Pseudomonas syringae pv. tomato strain B13-200. To identify the race 1, each strain was inoculated in five tomato plants cv. San Pedro, susceptible to both races of P. syringae pv. tomato, and cv. Rio Grande, resistant to race 0. The tomato plants were slightly wounded with a metal sponge and then sprayed with the bacterial suspension (108 CFU mL-1) of each isolate, including the reference strain DC3000 (race 0). Negative controls were sprayed with water. The plants inoculated with Chilean strains in both cv. San Pedro and cv. Rio Grande, showed symptoms of bacterial speck after 7 days. Plants inoculated with DC3000 strain showed symptoms only in cv. San Pedro, whereas control plants remained asymptomatic. Strains were re-isolated from symptomatic plants and identified by gene sequence analyses as Pseudomonas syryngae pv. tomato. This is the first report of Pseudomonas syryngae pv. tomato race 1 in Chile. Race 1 was previously reported in Canada (Lawton and MacNeill. 1986), in Italy (Buonaurio et al. 1996), in California (Arredondo and Davis 2000), in Portugal (Cruz et al. 2010), and in other states in the USA and countries in South America, Europe, Africa, and Australia, becoming the most commonly isolated race today (Cai et al 2011). These results will be the base for future studies of epidemiology, characterization, and virulence in order to explain the outbreak of this disease and the severity of symptoms observed.

Chemical Composition, Production of Secondary Metabolites and Antioxidant Activity in Coffee Cultivars Susceptible and Partially Resistant to Bacterial Halo Blight.

Coffee production is one of the main agricultural activities in Brazil, and several coffee cultivars with disease resistance have already been developed. The secondary metabolites produced by plants are closely associated with defense strategies, and the resistance of coffee cultivars to bacterial halo blight (BHB) can be related to these compounds. Therefore, this study aims to compare a partially resistant coffee cultivar (Iapar-59) and a susceptible cultivar (Mundo Novo 376/4) to BHB (Pseudomonas syringae pv. garcae) in relation to the chemical composition and antioxidant activity of the leaf extracts. In addition, this study determined the total phenolic and flavonoid contents and phenolic profiles of the Iapar-59 leaf extracts of plants inoculated with P. syringae pv. garcae. The Iapar-59 extract showed a higher content of phenolic compounds and flavonoids than the Mundo Novo 376/4 extract. Both cultivars contained gallic, chlorogenic and caffeic acids; however, the highest contents were quantified in the Iapar-59 cultivar. The leaf extracts from the Iapar-59 cultivar exhibited higher antioxidant activity. Higher concentrations of gallic, caffeic and chlorogenic acids and the presence of vanillin were detected in the extract of cultivar Iapar-59 inoculated with P. syringae pv. garcae.

The Pbo Cluster from Pseudomonas syringae pv. Phaseolicola NPS3121 Is Thermoregulated and Required for Phaseolotoxin Biosynthesis.

The bean (Phaseolus vulgaris) pathogen Pseudomonas syringae pv. phaseolicola NPS3121 synthesizes phaseolotoxin in a thermoregulated way, with optimum production at 18 °C. Gene PSPPH_4550 was previously shown to be thermoregulated and required for phaseolotoxin biosynthesis. Here, we established that PSPPH_4550 is part of a cluster of 16 genes, the Pbo cluster, included in a genomic island with a limited distribution in P. syringae and unrelated to the possession of the phaseolotoxin biosynthesis cluster. We identified typical non-ribosomal peptide synthetase, and polyketide synthetase domains in several of the pbo deduced products. RT-PCR and the analysis of polar mutants showed that the Pbo cluster is organized in four transcriptional units, including one monocistronic and three polycistronic. Operons pboA and pboO are both essential for phaseolotoxin biosynthesis, while pboK and pboJ only influence the amount of toxin produced. The three polycistronic units were transcribed at high levels at 18 °C but not at 28 °C, whereas gene pboJ was constitutively expressed. Together, our data suggest that the Pbo cluster synthesizes secondary metabolite(s), which could participate in the regulation of phaseolotoxin biosynthesis.

BiP-overexpressing soybean plants display accelerated hypersensitivity response (HR) affecting the SA-dependent sphingolipid and flavonoid pathways.

Biotic and abiotic environmental stresses have limited the increase in soybean productivity. Overexpression of the molecular chaperone BiP in transgenic plants has been associated with the response to osmotic stress and drought tolerance by maintaining cellular homeostasis and delaying hypersensitive cell death. Here, we evaluated the metabolic changes in response to the hypersensitivity response (HR) caused by the non-compatible bacteria Pseudomonas syringae pv. tomato in BiP-overexpressing plants. The HR-modified metabolic profiles in BiP-overexpressing plants were significantly distinct from the wild-type untransformed. The transgenic plants displayed a lower abundance of HR-responsive metabolites as amino acids, sugars, carboxylic acids and signal molecules, including p-aminobenzoic acid (PABA) and dihydrosphingosine (DHS), when compared to infected wild-type plants. In contrast, salicylic acid (SA) biosynthetic and signaling pathways were more stimulated in transgenic plants, and both pathogenesis-related genes (PRs) and transcriptional factors controlling the SA pathway were more induced in the BiP-overexpressing lines. Furthermore, the long-chain bases (LCBs) and ceramide biosynthetic pathways showed alterations in gene expression and metabolite abundance. Thus, as a protective pathway against pathogens, HR regulation by sphingolipids and SA may account at least in part by the enhanced resistance of transgenic plants. GmNAC32 transcriptional factor was more induced in the transgenic plants and it has also been reported to regulate flavonoid synthesis in response to SA. In fact, the BiP-overexpressing plants showed an increase in flavonoids, mainly prenylated isoflavones, as precursors for phytoalexins. Our results indicate that the BiP-mediated acceleration in the hypersensitive response may be a target for metabolic engineering of plant resistance against pathogens.