New Dry Edible Bean Resists Bacterial Disease
Agricultural Research, MD - Jun 29, 2007
Caused by the pathogen Xanthomonas campestris pv. phaseoli, bacterial blight is an endemic disease affecting bean crops east of the US Continental Divide. ...

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DinI and RecX modulate RecA-DNA structures in Escherichia coli K-12.

Mol Microbiol. 2007 Jan;63(1):103-15

Authors: Renzette N, Gumlaw N, Sandler SJ

RecA plays a central role in recombination, DNA repair and SOS induction through forming a RecA-DNA helical filament. Biochemical observations show that at low ratios to RecA, DinI and RecX stabilize and destabilize RecA-DNA filaments, respectively, and that the C-terminal 17 residues of RecA are important for RecX function. RecA-DNA filament formation was assayed in vivo using RecA-GFP foci formation in log-phase and UV-irradiated cells. In log-phase cells, dinI mutants have fewer foci than wild type and that recX mutants have more foci than wild type. A recADelta17::gfp mutant had more foci like a recX mutant. dinI recX double mutants have the same number of foci as dinI mutants alone, suggesting that dinI is epistatic to recX. After UV treatment, the dinI, recX and dinI recX mutants differed in their ability to form foci. All three mutants had fewer foci than wild type. The dinI mutant's foci persisted longer than wild-type foci. Roles of DinI and RecX after UV treatment differed from those during log-phase growth and may reflect the different DNA substrates, population of proteins or amounts during the SOS response. These experiments give new insight into the roles of these proteins.

PMID: 17163974 [PubMed - indexed for MEDLINE]

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Evolutionary pathways of an ancient gene recX.

Gene. 2007 Jan 31;387(1-2):15-20

Authors: Lin J, Chen ZZ, Tian B, Hua YJ

RecX is a regulator of RecA activity by interacting with RecA protein or RecA filaments. Genes encoding RecX were found in genomes of a wide diversity of bacteria and some plants (e.g., Arabidopsis thaliana and Oryza sativa). Our comparative genome analysis showed that although members of the RecX family are found in many bacterial species, they are not found in archaea and the only gene found in eukaryotes is likely derived from bacteria genomes. It is therefore proposed that RecX is of bacterial origin, and the gene had presented in the common ancestor of bacteria. Moreover, bacterial RecX and plant RecX domain are homologues, and RecX domain in plants may have derived from bacteria via unknown pathways. Plant RecX-like protein was formed by a gene fusion event between a unique N-terminal domain of unknown origin and RecX domain within plant cells. Finally, three possible evolutionary pathways from bacteria to plant were discussed.

PMID: 16996700 [PubMed - indexed for MEDLINE]

Argentina: canker in citrus worries growers
FreshPlaza, Netherlands - Jun 27, 2007
They are particularly worried about the so-called "cancrosis", highly contagious disease caused by "Xanthomonas campestris pathovar citri" bacteria. ...

Argentina: canker in citrus worries growers
FreshPlaza, Netherlands - Jun 27, 2007
They are particularly worried about the so-called "cancrosis", highly contagious disease caused by "Xanthomonas campestris pathovar citri" bacteria. ...

Argentina: canker in citrus worries growers
FreshPlaza, Netherlands - Jun 27, 2007
They are particularly worried about the so-called "cancrosis", highly contagious disease caused by "Xanthomonas campestris pathovar citri" bacteria. ...

Argentina: canker in citrus worries growers
FreshPlaza, Netherlands - Jun 27, 2007
They are particularly worried about the so-called "cancrosis", highly contagious disease caused by "Xanthomonas campestris pathovar citri" bacteria. ...

Argentina: canker in citrus worries growers
FreshPlaza, Netherlands - Jun 27, 2007
They are particularly worried about the so-called "cancrosis", highly contagious disease caused by "Xanthomonas campestris pathovar citri" bacteria. ...

Argentina: canker in citrus worries growers
FreshPlaza, Netherlands - Jun 27, 2007
They are particularly worried about the so-called "cancrosis", highly contagious disease caused by "Xanthomonas campestris pathovar citri" bacteria. ...

Argentina: canker in citrus worries growers
FreshPlaza, Netherlands - Jun 27, 2007
They are particularly worried about the so-called "cancrosis", highly contagious disease caused by "Xanthomonas campestris pathovar citri" bacteria. ...

Argentina: canker in citrus worries growers
FreshPlaza, Netherlands - Jun 27, 2007
They are particularly worried about the so-called "cancrosis", highly contagious disease caused by "Xanthomonas campestris pathovar citri" bacteria. ...

Argentina: canker in citrus worries growers
FreshPlaza, Netherlands - Jun 27, 2007
They are particularly worried about the so-called "cancrosis", highly contagious disease caused by "Xanthomonas campestris pathovar citri" bacteria. ...

Argentina: canker in citrus worries growers
FreshPlaza, Netherlands - Jun 27, 2007
They are particularly worried about the so-called "cancrosis", highly contagious disease caused by "Xanthomonas campestris pathovar citri" bacteria. ...

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Detection of Xanthomonas fragariae and presumptive detection of Xanthomonas arboricola pv. fragariae, from strawberry leaves, by real-time PCR.

J Microbiol Methods. 2007 May 31;

Authors: Weller SA, Beresford-Jones NJ, Hall J, Thwaites R, Parkinson N, Elphinstone JG

Real-time (TaqMan) PCR assays were developed to detect the strawberry angular leaf spot pathogen Xanthomonas fragariae (Xf) and the strawberry bacterial blight pathogen Xanthomonas arboricola pv. fragariae (Xaf). The Xf PCR (Xf gyrB) was designed within regions of the gyraseB gene, unique to Xf, after generating gyraseB DNA sequence data from Xf and other closely related strains. The Xaf PCR (Xaf pep) was designed within regions of the pep prolyl endopeptidase gene that were unique to Xaf, after generating pep DNA sequence data from Xf and Xaf strains. The Xf gyrB PCR detected only Xf strains amongst a panel of 20 Xanthomonas-related spp. and pathovars. The Xaf pep PCR assay detected all Xaf strains tested plus two other (of three tested) X. arboricola pathovars. An existing genomic DNA extraction protocol was modified to facilitate detection of both pathogens to 10(3) cells per strawberry leaf disc.

PMID: 17588695 [PubMed - as supplied by publisher]

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Capsicum annuum CCR4-associated factor CaCAF1 is necessary for plant development and defence response.

Plant J. 2007 Jul 21;

Authors: Sarowar S, Oh HW, Cho HS, Baek KH, Seong ES, Joung YH, Choi GJ, Lee S, Choi D

The CCR4-associated factor 1 (CAF1) protein belongs to the CCR4-NOT complex, which is an evolutionary conserved protein complex and plays an important role in the control of transcription and mRNA decay in yeast and mammals. To investigate the function of CAF1 in plants, we performed gain- and loss-of-function studies by overexpression of the pepper CAF1 (CaCAF1) in tomato and virus-induced gene silencing (VIGS) of the gene in pepper plants. Overexpression of CaCAF1 in tomato resulted in significant growth enhancement, with increasing leaf thickness, and enlarged cell size by more than twofold when compared with the control plants. A transmission electron microscopic analysis revealed that the CaCAF1-transgenic tomato plants had thicker cell walls and cuticle layers than the control plants. In addition to developmental changes, overexpression of CaCAF1 in tomato plants resulted in enhanced resistance against the oomycete pathogen Phytophthora infestans. Additionally, microarray, northern and real-time polymerase chain reaction analyses of CaCAF1-transgenic tomato plants revealed that multiple genes were constitutively upregulated, including genes involved in polyamine biosynthesis, defence reactions and cell-wall organogenesis. In contrast, VIGS of CaCAF1 in pepper plants caused significant growth retardation and enhanced susceptibility to the pepper bacterial spot pathogen Xanthomonas axonopodis pv. vesicatoria. Our results suggest roles for plant CAF1 in normal growth and development, as well as in defence against pathogens.

PMID: 17587232 [PubMed - as supplied by publisher]

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Transcriptional analysis of the tomato resistance response triggered by recognition of the Xanthomonas type III effector AvrXv3.

Funct Integr Genomics. 2007 Jun 21;

Authors: Balaji V, Gibly A, Debbie P, Sessa G

The type III effector AvrXv3 from Xanthomonas campestris pv. vesicatoria (Xcv) elicits a resistance response in the tomato line Hawaii 7981. To test whether similar genes participate in responses triggered by recognition of different avirulence proteins, we examined the effect of AvrXv3 expression on the plant transcriptome as compared to that of other avirulence proteins. By microarray analysis we monitored expression of approximately 8,600 tomato genes upon inoculation with isogenic Xcv strains differing only by the avrXv3 gene. Changes in transcript levels of 139 genes were observed within 8 h, and a massive shift in expression of 1,294 genes was detected at 12 h. Recognition of AvrXv3 modulated a large number of genes encoding transcription factors and signaling components. In addition, genes involved in defense and stress responses, lipid metabolism, protein degradation, and secondary metabolism were mainly up-regulated. Conversely, genes related to photosynthesis and protein synthesis were generally down-regulated. Many novel genes encoding proteins of unknown function were also identified. A comparison between AvrXv3-modulated genes and those differentially expressed in tomato plants recognizing other bacterial effectors revealed partial overlap and similar distribution in functional classes. The identification of tomato genes modulated by AvrXv3 expression paves the way for dissecting defense networks activated by recognition of this effector in resistant plants.

PMID: 17582538 [PubMed - as supplied by publisher]

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A proline iminopeptidase gene upregulated in planta by a LuxR homologue is essential for pathogenicity of Xanthomonas campestris pv. campestris.

Mol Microbiol. 2007 Jul;65(1):121-136

Authors: Zhang L, Jia Y, Wang L, Fang R

Expression of bacterial genes is often regulated by complex mechanisms, some of which involve host cues. Analysis of the Xanthomonas campestris pv. campestris (Xcc) genome sequence revealed the presence of an xccR/pip locus. The upstream gene xccR is a luxR homologue, while pip codes for a proline iminopeptidase. A lux box-like element, named luxXc box, locates in the pip promoter region. In this work, we show that disruption of either xccR or pip resulted in significantly attenuated virulence of Xcc. Under medium culture conditions, the pip expression was significantly enhanced by overexpression of XccR and the luxXc box is necessary for this enhancement. We further show that expression of a pip promoter-gusA fusion either inserted in the bacterial chromosome or resided in a plasmid was markedly induced when the bacteria grew in planta. Disruption of either xccR or the luxXc box abolished the in planta induction, while disruption of pip enhanced the induction. Taken together, these data demonstrate that pip is indispensable for Xcc virulence and suggest a model for Xcc-host interaction in which the pathogen senses some host factor(s) to activate XccR that subsequently interacts with the luxXc box to induce the expression of pip for facilitating Xcc infection.

PMID: 17581124 [PubMed - as supplied by publisher]

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A novel pathway for the biodegradation of gamma-hexachlorocyclohexane by a Xanthomonas sp. strain ICH12.

J Appl Microbiol. 2007 Jun;102(6):1468-78

Authors: Manickam N, Misra R, Mayilraj S

AIM: To isolate gamma-hexachlorocyclohexane (HCH)-degrading bacteria from contaminated soil and characterize the metabolites formed and the genes involved in the degradation pathway. METHODS AND RESULTS: A bacterial strain Xanthomonas sp. ICH12, capable of biodegrading gamma- HCH was isolated from HCH-contaminated soil. DNA-colony hybridization method was employed to detect bacterial populations containing specific gene sequences of the gamma-HCH degradation pathway. linA (dehydrodehalogenase), linB (hydrolytic dehalogenase) and linC (dehydrogenase) from a Sphingomonas paucimobilis UT26, reportedly possessing gamma-HCH degradation activity, were used as gene probes against isolated colonies. The isolate was found to grow and utilize gamma-HCH as the sole carbon and energy source. The 16S ribosomal RNA gene sequence of the isolate resulted in its identification as a Xanthomonas species, and we designated it as strain ICH12. During the degradation of gamma-HCH by ICH12, formation of two intermediates, gamma-2,3,4,5,6-pentachlorocyclohexene (gamma-PCCH), and 2,5-dichlorobenzoquinone (2,5-DCBQ), were identified by gas chromatography-mass spectrometric (GC-MS) analysis. While gamma-PCCH was reported previously, 2,5-dichlorohydroquinone was a novel metabolite from HCH degradation. CONCLUSIONS: A Xanthomonas sp. for gamma-HCH degradation from a contaminated soil was isolated. gamma-HCH was utilized as sole source of carbon and energy, and the degradation proceeds by successive dechlorination. Two degradation products gamma-PCCH and 2,5-DCBQ were characterized, and the latter metabolite was not known in contrasts with the previous studies. The present work, for the first time, demonstrates the potential of a Xanthomonas species to degrade a recalcitrant and widespread pollutant like gamma-HCH. SIGNIFICANCE AND IMPACT OF THE STUDY: This study demonstrates the isolation and characterization of a novel HCH-degrading bacterium. Further results provide an insight into the novel degradation pathway which may exist in diverse HCH-degrading bacteria in contaminated soils leading to bioremediation of gamma-HCH.

PMID: 17578411 [PubMed - in process]

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Epigenetic Inheritance in Rice Plants.

Ann Bot (Lond). 2007 Jun 18;

Authors: Akimoto K, Katakami H, Kim HJ, Ogawa E, Sano CM, Wada Y, Sano H

Background and Aims Epigenetics is defined as mechanisms that regulate gene expression without base sequence alteration. One molecular basis is considered to be DNA cytosine methylation, which reversibly modifies DNA or chromatin structures. Although its correlation with epigenetic inheritance over generations has been circumstantially shown, evidence at the gene level has been limited. The present study aims to find genes whose methylation status directly correlates with inheritance of phenotypic changes. Methods DNA methylation in vivo was artificially reduced by treating rice (Oryza sativa ssp. japonica) seeds with 5-azadeoxycytidine, and the progeny were cultivated in the field for >10 years. Genomic regions with changed methylation status were screened by the methylation-sensitive amplified polymorphysm (MSAP) method, and cytosine methylation was directly scanned by the bisulfite mapping method. Pathogen infection with Xanthomonas oryzae pv. oryzae, race PR2 was performed by the scissors-dip method on mature leaf blades. Key Results The majority of seedlings were lethal, but some survived to maturity. One line designated as Line-2 showed a clear marker phenotype of dwarfism, which was stably inherited by the progeny over nine generations. MSAP screening identified six fragments, among which two were further characterized by DNA blot hybridization and direct methylation mapping. One clone encoding a retrotransposon gag-pol polyprotein showed a complete erasure of 5-methylcytosines in Line-2, but neither translocation nor expression of this region was detectable. The other clone encoded an Xa21-like protein, Xa21G. In wild-type plants, all cytosines were methylated within the promoter region, whereas in Line-2, corresponding methylation was completely erased throughout generations. Expression of Xa21G was not detectable in wild type but was constitutive in Line-2. When infected with X. oryzae pv. oryzae, against which Xa21 confers resistance in a gene-for-gene manner, the progeny of Line-2 were apparently resistant while the wild type was highly susceptible without Xa21G expression. Conclusions These results indicated that demethylation was selective in Line-2, and that promoter demethylation abolished the constitutive silencing of Xa21G due to hypermethylation, resulting in acquisition of disease resistance. Both hypomethylation and resistant trait were stably inherited. This is a clear example of epigenetic inheritance, and supports the idea of Lamarckian inheritance which suggested acquired traits to be heritable.

PMID: 17576658 [PubMed - as supplied by publisher]

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Identification of Xanthomonas campestris pv. vesicatoria Genes Induced in its Interaction with Tomato.

J Bacteriol. 2007 Jun 15;

Authors: Tamir-Ariel D, Navon N, Burdman S

Xanthomonas campestris pv. vesicatoria (Xcv) is the causal agent of bacterial spot disease of tomato and pepper. The disease process is interactive and very intricate, and involves a plethora of genes in the pathogen and in the host. In the pathogen, different genes are activated in response to the changing environment to enable it to survive, adapt, evade host defenses, propagate, and damage the host. To understand the disease process it is imperative to broaden our understanding of the gene machinery that participates in it, and the most reliable way is to identify these genes in vivo. Here, we have adapted a Recombinase-based In Vivo Expression Technology (RIVET) to study the genes activated in Xcv during its interaction with one of its hosts, tomato. This is the first study that demonstrates the feasibility of this approach for identifying in vivo induced genes in a plant pathogen. RIVET revealed 61 unique Xcv genes that delineate a picture of the different processes involved in pathogen-host interaction. To further explore the role of some of these genes, we generated knockout mutants for 13 genes and characterized their ability to grow in planta and to cause disease symptoms. This analysis revealed several genes that may be important for the interaction of the pathogen with its host, including a citH homologue gene, encoding a citrate transporter, which was shown to be required for wild type levels of virulence.

PMID: 17573477 [PubMed - as supplied by publisher]