81 research outputs found
Panicle sterility and grain discolouration : new and emerging bacterial diseases of rice in Italy
No full textIn Italy, panicle sterility and grain discolouration have emerged as serious problems throughout the rice growing areas. Surveys showed that the incidence of panicle sterility was highly variable, varying from low, barely observable in some fields, to more than 50% in other ones. In the Lombardy region the estimated average crop loss due to sterility was 1.1% and 0.1% in 2003 and 2004, respectively. Grain discolouration reduces rice quality. At harvest, susceptible cultivars can have more than 30% discoloured grains. The etiology for both diseases is uncertain and early diagnosis difficult because diseased plants are symptomless. We have demonstrated for the first time that both diseases have a bacterial etiology. Bacterial colonies typical of Acidovorax avenae subsp. avenae were purified from sterile panicles and discoloured rice samples. All recovered strains were confirmed as Aaa by classical PCR using Aaa-specific primers. Isolation of Aaa on a semi-selective agar medium did not always work well. However, an improved BIO-PCR assay was used to test 113 sterile panicle samples and 74% were positive for the presence of Aaa, but negative for Burkholderia glumae (Bg). The bacteria associated with discoloured grains were mostly composed of Pseudomonas and Pantoea species. Based on the 16S rDNA sequences, 85% of the pseudomonads population was classified as P. straminea, P. fulva, P. putida, P. psychrotolerans, P. stutzeri and P. fluorescens. Aaa and Pseudomonas strains were tested for pathogenicity on seedlings in the greenhouse and on plants at the booting stage in the field. Strains of Aaa caused soft rotting of seedlings, panicle sterility and grain discolouration and they showed significant intraspecific variation for virulence. Although most Pseudomonas spp. were not pathogenic, strains of P. stutzeri and strains presumptively identified as P. fulva induced grain discolouration incidence significantly higher than the control. In addition, we have found, for the first time, P. ananatis on rice in Italy
Gene Ontology (GO) for Microbe–Host Interactions and Its Use in Ongoing Annotation of Three Pseudomonas syringae Genomes via the Pseudomonas–Plant Interaction (PPI) Web Site
No full textPeter Collmer, Verwaltete Vielfalt. Die königlichen Tafelgüter in Polen-Litauen, 1697–1763
No full textSyringolin A: action on plants, regulation of biosynthesis, and phylogenetic occurrence of structurally related compounds
No full textSyringolin A, the product of a mixed non-ribosomal peptide/polyketide synthetase, is secreted by Pseudomonas syringae pv. syringae under in planta conditions and is one of the molecular determinants recognized by nonhost plant species. Spray application of syringolin A onto powdery mildew-infected wheat and Arabidopsis has the remarkable effect of reprogramming epidermal cells that are colonized by the powdery mildew fungi Blumeria graminis f. sp. tritici and Erysiphe cichoracearum, respectively, in a compatible interaction to undergo hypersensitive cell death. No hypersensitive cell death is observed if the compound is applied onto uninfected plants. Transcriptome analyses in wheat and Arabidopsis with regard to powdery mildew inoculation and/or syringolin A spraying lead to a hypothesis about how syringolin A may accomplish to induce the hypersensitive reaction (HR) in colonized cells. The model is supported by transcriptome analyis of an Arabidopsis mutant in which HR is not induced upon syringolin A spraying of powdery mildew-infected plants. Cloning of the syringolin A synthetase genes has allowed us to build a detailed model of syringolin A synthesis based on the gene structure. This model in turn enabled us to clone the genes responsible for the synthesis of glidobactins (syn. cepafungins), antibiotics with a structure related to syringolin A that were reported to have antitumor activity, from an unknown species belonging to the order Burkholderiales. Comparisons to the approximately 700 complete eubacterial genomic sequences known resulted in the identification of a small but very intriguing group of pathogenic bacteria postulated to produce glidobacting-like molecules
The Irish potato famine pathogen Phytophthora infestans translocates the CRN8 kinase into host plant cells
No full textPhytopathogenic oomycetes, such as Phytophthora infestans, secrete an arsenal of effector proteins that modulate plant innate immunity to enable infection. We describe CRN8, a host-translocated effector of P. infestans that has kinase activity in planta. CRN8 is a modular protein of the CRN effector family. The C-terminus of CRN8 localizes to the host nucleus and triggers cell death when the protein is expressed in planta. Cell death induction by CRN8 is dependent on its localization to the plant nucleus, which requires a functional nuclear localization signal (NLS). The C-terminal sequence of CRN8 has similarity to a serine/threonine RD kinase domain. We demonstrated that CRN8 is a functional RD kinase and that its auto-phosphorylation is dependent on an intact catalytic site. Co-immunoprecipitation experiments revealed that CRN8 forms a dimer or multimer. Heterologous expression of CRN8 in planta resulted in enhanced virulence by P. infestans. In contrast, in planta expression of the dominant-negative CRN8R469A;D470A resulted in reduced P. infestans infection, further implicating CRN8 in virulence. Overall, our results indicate that similar to animal parasites, plant pathogens also translocate biochemically active kinase effectors inside host cells
The molecular basis of host specialization in bean pathovars of Pseudomonas syringae
No full textBiotrophic phytopathogens are typically limited to their
adapted host range. In recent decades, investigations have
teased apart the general molecular basis of intraspecific
variation for innate immunity of plants, typically involving
receptor proteins that enable perception of pathogen-associated
molecular patterns or avirulence elicitors from the
pathogen as triggers for defense induction. However, general
consensus concerning evolutionary and molecular factors
that alter host range across closely related phytopathogen
isolates has been more elusive. Here, through genome
comparisons and genetic manipulations, we investigate the
underlying mechanisms that structure host range across
closely related strains of Pseudomonas syringae isolated
from different legume hosts. Although type III secretionindependent
virulence factors are conserved across these
three strains, we find that the presence of two genes encoding
type III effectors (hopC1 and hopM1) and the absence
of another (avrB2) potentially contribute to host range differences
between pathovars glycinea and phaseolicola.
These findings reinforce the idea that a complex genetic
basis underlies host range evolution in plant pathogens.
This complexity is present even in host–microbe interactions
featuring relatively little divergence among both hosts
and their adapted pathogens
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Comparative genome analysis provides insights into the evolution and adaptation of Pseudomonas syringae pv. aesculi on Aesculus hippocastanum.
No full textA recently emerging bleeding canker disease, caused by Pseudomonas syringae pathovar aesculi (Pae), is threatening
European horse chestnut in northwest Europe. Very little is known about the origin and biology of this new disease. We
used the nucleotide sequences of seven commonly used marker genes to investigate the phylogeny of three strains isolated
recently from bleeding stem cankers on European horse chestnut in Britain (E-Pae). On the basis of these sequences alone, the E-Pae strains were identical to the Pae type-strain (I-Pae), isolated from leaf spots on Indian horse chestnut in India in 1969. The phylogenetic analyses also showed that Pae belongs to a distinct clade of P. syringae pathovars adapted to woody hosts. We generated genome-wide Illumina sequence data from the three E-Pae strains and one strain of I-Pae. Comparative genomic analyses revealed pathovar-specific genomic regions in Pae potentially implicated in virulence on a tree host,
including genes for the catabolism of plant-derived aromatic compounds and enterobactin synthesis. Several gene clusters displayed intra-pathovar variation, including those encoding type IV secretion, a novel fatty acid biosynthesis pathway and a sucrose uptake pathway. Rates of single nucleotide polymorphisms in the four Pae genomes indicate that the three E-Pae strains diverged from each other much more recently than they diverged from I-Pae. The very low genetic diversity among the three geographically distinct E-Pae strains suggests that they originate from a single, recent introduction into Britain, thus highlighting the serious environmental risks posed by the spread of an exotic plant pathogenic bacterium to a new geographic location. The genomic regions in Pae that are absent from other P. syringae pathovars that infect herbaceous hosts may represent candidate genetic adaptations to infection of the woody parts of the tree
Chemical and biological characterisation of tolaasins A-E: new lipodepsipeptides produced by Pseudomonas tolaasii.
No full textPseudomonas tolaasii, the causal agent of brown blotch disease of Agaricus bisporusand of the yellowing of Pleurotus ostreatus, produces in culture an extracellular toxin, called tolaasin I, which has been shown to have an important role in the development of disease symptoms. The toxin, previously characterized as a lipodepsipeptide with a long and hydrophobic peptide chain, was isolated from the culture filtrates together with tolaasin II, a minor component structurally related to tolaasin I. This paper reports the preliminary structural elucidation data (based on NMR studies and MS spectra) and biological activity of four minor analogues, named tolaasins A, B, D and E, as well as the complete characterization of the tolaasin C
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