Chemosensory systems interact to shape relevant traits for bacterial plant pathogenesis.

Unlabelled: Chemosensory systems allow bacteria to respond and adapt to environmental conditions. Many bacteria contain more than one chemosensory system, but knowledge of their specific roles in regulating different functions remains scarce. Here, we address this issue by analyzing the function of the F6, F8, and alternative (non-motility) cellular functions (ACF) chemosensory systems of the model plant pathogen pv.

Functional and evolutionary significance of unknown genes from uncultivated taxa.

Many of the Earth's microbes remain uncultured and understudied, limiting our understanding of the functional and evolutionary aspects of their genetic material, which remain largely overlooked in most metagenomic studies. Here we analysed 149,842 environmental genomes from multiple habitats and compiled a curated catalogue of 404,085 functionally and evolutionarily significant novel (FESNov) gene families exclusive to uncultivated prokaryotic taxa. All FESNov families span multiple species, exhibit strong signals of purifying selection and qualify as new orthologous groups, thus nearly tripling the number of bacterial and archaeal gene families described to date.

A Nitrate-Sensing Domain-Containing Chemoreceptor Is Required for Successful Entry and Virulence of 3937 in Potato Plants.

Nitrate metabolism plays an important role in bacterial physiology. During the interaction of plant-pathogenic bacteria with their hosts, bacteria face variable conditions with respect to nitrate availability. Perception mechanisms through the chemosensory pathway drive the entry and control the colonization of the plant host in phytopathogenic bacteria.

Pseudomonas syringae pv. tomato infection of tomato plants is mediated by GABA and l-Pro chemoperception.

Foliar bacterial pathogens have to penetrate the plant tissue and access the interior of the apoplast in order to initiate the pathogenic phase. The entry process is driven by chemotaxis towards plant-derived compounds in order to locate plant openings. However, information on plant signals recognized by bacterial chemoreceptors is scarce.

Prevalence and Specificity of Chemoreceptor Profiles in Plant-Associated Bacteria.

Chemosensory pathways are among the most abundant prokaryotic signal transduction systems, allowing bacteria to sense and respond to environmental stimuli. Signaling is typically initiated by the binding of specific molecules to the igand inding omain (LBD) of hemoeceptor proteins (CRs). Although CRs play a central role in plant-microbiome interactions such as colonization and infection, little is known about their phylogenetic and ecological specificity.

Blue-light perception by epiphytic Pseudomonas syringae drives chemoreceptor expression, enabling efficient plant infection.

Adaptation and efficient colonization of the phyllosphere are essential processes for the switch to an epiphytic stage in foliar bacterial pathogens. Here, we explore the interplay among light perception and global transcriptomic alterations in epiphytic populations of the hemibiotrophic pathogen Pseudomonas syringae pv. tomato DC3000 (PsPto) following contact with tomato leaves.

Chemoperception of Specific Amino Acids Controls Phytopathogenicity in Pseudomonas syringae pv. tomato.

Chemotaxis has been associated with the pathogenicity of bacteria in plants and was found to facilitate bacterial entry through stomata and wounds. However, knowledge regarding the plant signals involved in this process is scarce. We have addressed this issue using pv.

The Pseudomonas syringae pv. tomato DC3000 PSPTO_0820 multidrug transporter is involved in resistance to plant antimicrobials and bacterial survival during tomato plant infection.

Multidrug resistance efflux pumps protect bacterial cells against a wide spectrum of antimicrobial compounds. PSPTO_0820 is a predicted multidrug transporter from the phytopathogenic bacterium Pseudomonas syringae pv. tomato DC3000.

Pseudomonas syringae pv. tomato exploits light signals to optimize virulence and colonization of leaves.

Light is pervasive in the leaf environment, creating opportunities for both plants and pathogens to cue into light as a signal to regulate plant-microbe interactions. Light enhances plant defences and regulates opening of stomata, an entry point for foliar bacterial pathogens such as Pseudomonas syringae pv. tomato DC3000 (PsPto).

Suppression of Plant Immune Responses by the pv. NCPPB 3335 Type III Effector Tyrosine Phosphatases HopAO1 and HopAO2.

The effector repertoire of the olive pathogen pv. NCPPB 3335 includes two members of the HopAO effector family, one of the most diverse T3E families of the complex. The study described here explores the phylogeny of these dissimilar members, HopAO1 and HopAO2, among the complex and reveals their activities as immune defense suppressors.

Prediction of bacterial associations with plants using a supervised machine-learning approach.

Recent scenarios of fresh produce contamination by human enteric pathogens have resulted in severe food-borne outbreaks, and a new paradigm has emerged stating that some human-associated bacteria can use plants as secondary hosts. As a consequence, there has been growing concern in the scientific community about these interactions that have not yet been elucidated. Since this is a relatively new area, there is a lack of strategies to address the problem of food-borne illnesses due to the ingestion of fruits and vegetables.

Differential modulation of plant immune responses by diverse members of the Pseudomonas savastanoi pv. savastanoi HopAF type III effector family.

The Pseudomonas savastanoi pv. savastanoi NCPPB 3335 type III secretion system (T3SS) effector repertoire includes 33 candidates, seven of which translocate into host cells and interfere with plant defences. The present study was performed to investigate the co-existence of both plasmid- and chromosomal-encoded members of the HopAF effector family, HopAF1-1 and HopAF1-2, respectively, in the genome of NCPPB 3335.

Temporal and Spatial Resolution of Activated Plant Defense Responses in Leaves of Nicotiana benthamiana Infected with Dickeya dadantii.

The necrotrophic bacteria Dickeya dadantii is the causal agent of soft-rot disease in a broad range of hosts. The model plant Nicotiana benthamiana, commonly used as experimental host for a very broad range of plant pathogens, is susceptible to infection by D. dadantii.

Role of Dickeya dadantii 3937 chemoreceptors in the entry to Arabidopsis leaves through wounds.

Chemotaxis enables bacteria to move towards an optimal environment in response to chemical signals. In the case of plant-pathogenic bacteria, chemotaxis allows pathogens to explore the plant surface for potential entry sites with the ultimate aim to prosper inside plant tissues and to cause disease. Chemoreceptors, which constitute the sensory core of the chemotaxis system, are usually transmembrane proteins which change their conformation when sensing chemicals in the periplasm and transduce the signal through a kinase pathway to the flagellar motor.

N2O and CH4 emissions from a fallow-wheat rotation with low N input in conservation and conventional tillage under a Mediterranean agroecosystem.

Conservation agriculture that includes no tillage (NT) or minimum tillage (MT) and crop rotation is an effective practice to increase soil organic matter in Mediterranean semiarid agrosystems. But the impact of these agricultural practices on greenhouse gases (GHGs), such as nitrous oxide (N2O) and methane (CH4), is variable depending mainly on soil structure and short/long-term tillage. The main objective of this study was to assess the long-term effect of three tillage systems (NT, MT and conventional tillage (CT)) and land-covers (fallow/wheat) on the emissions of N2O and CH4 in a low N input agricultural system during one year.

Exploring new roles for the rpoS gene in the survival and virulence of the fire blight pathogen Erwinia amylovora.

Erwinia amylovora causes fire blight in economically important plants of the family Rosaceae. This bacterial pathogen spends part of its life cycle coping with starvation and other fluctuating environmental conditions. In many Gram-negative bacteria, starvation and other stress responses are regulated by the sigma factor RpoS.

Translocation and functional analysis of Pseudomonas savastanoi pv. savastanoi NCPPB 3335 type III secretion system effectors reveals two novel effector families of the Pseudomonas syringae complex.

Pseudomonas savastanoi pv. savastanoi NCPPB 3335 causes olive knot disease and is a model pathogen for exploring bacterial infection of woody hosts. The type III secretion system (T3SS) effector repertoire of this strain includes 31 effector candidates plus two novel candidates identified in this study which have not been reported to translocate into plant cells.

Jasmonate-dependent modifications of the pectin matrix during potato development function as a defense mechanism targeted by Dickeya dadantii virulence factors.

The plant cell wall constitutes an essential protection barrier against pathogen attack. In addition, cell-wall disruption leads to accumulation of jasmonates (JAs), which are key signaling molecules for activation of plant inducible defense responses. However, whether JAs in return modulate the cell-wall composition to reinforce this defensive barrier remains unknown.

Light regulates motility, attachment and virulence in the plant pathogen Pseudomonas syringae pv tomato DC3000.

Pseudomonas syringae pv tomato DC3000 (Pto) is the causal agent of the bacterial speck of tomato, which leads to significant economic losses in this crop. Pto inhabits the tomato phyllosphere, where the pathogen is highly exposed to light, among other environmental factors. Light represents a stressful condition and acts as a source of information associated with different plant defence levels.

The role of secretion systems and small molecules in soft-rot Enterobacteriaceae pathogenicity.

Soft-rot Enterobacteriaceae (SRE), which belong to the genera Pectobacterium and Dickeya, consist mainly of broad host-range pathogens that cause wilt, rot, and blackleg diseases on a wide range of plants. They are found in plants, insects, soil, and water in agricultural regions worldwide. SRE encode all six known protein secretion systems present in gram-negative bacteria, and these systems are involved in attacking host plants and competing bacteria.

A bacterial cysteine protease effector protein interferes with photosynthesis to suppress plant innate immune responses.

The bacterial pathogen Pseudomonas syringae pv tomato DC3000 suppresses plant innate immunity with effector proteins injected by a type III secretion system (T3SS). The cysteine protease effector HopN1, which reduces the ability of DC3000 to elicit programmed cell death in non-host tobacco, was found to also suppress the production of defence-associated reactive oxygen species (ROS) and callose when delivered by Pseudomonas fluorescens heterologously expressing a P. syringae T3SS.

Genome-wide analysis of the response of Dickeya dadantii 3937 to plant antimicrobial peptides.

Antimicrobial peptides constitute an important factor in the defense of plants against pathogens, and bacterial resistance to these peptides have previously been shown to be an important virulence factor in Dickeya dadantii, the causal agent of soft-rot disease of vegetables. In order to understand the bacterial response to antimicrobial peptides, a transcriptional microarray analysis was performed upon treatment with sub-lethal concentration of thionins, a widespread plant peptide. In all, 36 genes were found to be overexpressed, and were classified according to their deduced function as i) transcriptional regulators, ii) transport, and iii) modification of the bacterial membrane.

Annotation and overview of the Pseudomonas savastanoi pv. savastanoi NCPPB 3335 draft genome reveals the virulence gene complement of a tumour-inducing pathogen of woody hosts.

Pseudomonas savastanoi pv. savastanoi is a tumour-inducing pathogen of Olea europaea L. causing olive knot disease.

The Tat pathway of plant pathogen Dickeya dadantii 3937 contributes to virulence and fitness.

Protein secretion plays a very important role in the virulence of the bacterium Dickeya dadantii, the causative agent of soft rot disease, in a wide range of plant species. We studied the contribution of the twin-arginine translocation (Tat) protein system to the adaptation of D. dadantii 3937 to different growth conditions and to the interaction with the plant host.