Bacteriophage OP1, lytic for Xanthomonas oryzae pv. oryzae, changes its host range by duplication and deletion of the small domain in the deduced tail fiber gene

The entire genome of bacteriophage OP₁, lytic for Xanthomonas oryzae pv. oryzae causing bacterial leaf blight of rice, and the partial genomes of related phages were sequenced and analyzed. The OP₁ genome comprises double-stranded, 4785-bp long DNA with 51.1% G + C content. Fifty-nine open reading frames (ORFs) were detected. ORF25 had similarity with the tail fiber gene of phages, whose product is related to host specificity. The ORF25 regions were amplified from four host-range mutants (OP_1h, OP_1hC, OP_1h2, and OP_1h2C) by polymerase chain reaction, and their deduced amino acid sequences were compared. Three mutants (OP_1hC, OP_1h2, OP_1h2C) had duplications of a small domain in the N-terminal portion, although there were slight differences in the position of the duplicated sequences. One mutant OP_1h had substituted amino acids in the duplication region. New mutants isolated in the laboratory (OP_1hC and OP_1h2C from OP₁ and OP_1h2) acquired the ability to lyse strain N5874 belonging to phagovar (lysotype) C. However, they rapidly lost this lytic ability when incubated with other phagovars. This loss was always accompanied by a loss of the characteristic repeats, suggesting that the host range of OP₁-related phages changed mainly through duplication and deletion of a small domain in ORF25. The nucleotide sequence data reported are available in the DDBJ/EMBL/GenBank databases under the accession numbers AP008979, AB214312 to AB214316     

The genetic structure of populations of <Emphasis Type="Italic">Turnip mosaic virus</Emphasis> in Kyushu and central Honshu,Japan

The genetic structure of the populations of Turnip mosaic virus in Kyushu and central Honshu, Japan was assessed. The host specificity of isolates was determined, and their gene sequences compared utilizing a population genetic approach. Phylogenetic analysis of partial sequences revealed that 32 of 49 Honshu isolates (65%) collected during 1997–2001 belonged to the basal-BR group as did 23 of 64 isolates from Kyushu. All these basal-BR isolates infected both Brassica and Raphanus plants. However, analyses of the positions of recombination sites in five regions of the genome (one third of the full sequence) showed that at least four intra-lineage recombinants were present in these populations. These analyses showed that Kyushu and Honshu shared none of these subpopulations, and genetically distinct basal-BR populations were present in the two districts. We conclude that different basal-BR subpopulations had expanded into those districts. The nucleotide sequences are deposited in the DDBJ/EMBL/GenBank databases under accession numbers AB267281-AB267376.     

N-terminal domain including conserved flg22 is required for flagellin-induced hypersensitive cell death in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

Flagellin in Pseudomonas syringae is a potent elicitor of defense responses including hypersensitive cell death in dicot plants. The oligopeptides flg22 consisting of 22 conserved amino acids near the N-terminus of flagellins is reported to induce plant defense responses. Because glycosylation of the central domain of flagellin affects its elicitor activity, we investigated whether any peptide sequence in addition to flg22 is required for flagellin-induced hypersensitive reaction. A study of recombinant flagellin polypeptides indicated that the N-terminal domain including the conserved flg22 is required for flagellin-induced hypersensitive cell death in Arabidopsis thaliana.     

Propanil and swep inhibit 4-coumarate:CoA ligase activity in vitro

4-Coumarate:CoA ligase (4CL, EC 6.2.1.12) in the phenylpropanoid pathway in plants has attracted interest as a novel target for developing effective plant growth inhibitors (PGIs). In a previous study in which the 4CL inhibitory activity of 28 existing herbicides was investigated using an optimized in vitro screening assay, 4CL activity was found to be strongly inhibited by propanil and swep at 100 microM. Here, further experimental evidence is provided to substantiate the previous result. Using 4-coumaric acid as substrate, tobacco 4CL activity was inhibited by propanil or swep in a concentration-dependent manner, with 50% inhibition concentrations (I(50)) of 39.6 and 6 microM respectively. These herbicides also exhibited uncompetitive inhibition towards 4-coumaric acid. Furthermore, 4CLs from several plant species were inhibited by the herbicides within a range from 1 to 50 microM. It is proposed that these herbicides have another site of action as a result of the inhibition of 4CL in the phenylpropanoid pathway, and this enzyme represents a new target site for the development of PGI.     

AlgU contributes to the virulence of <Emphasis Type="Italic">Pseudomonas syringae</Emphasis> pv. <Emphasis Type="Italic">tomato</Emphasis> DC3000 by regulating production of the phytotoxin coronatine

Pseudomonas syringae pv. tomato DC3000 (Pst DC3000), which causes bacterial speck disease of tomato, has been used as a model pathogen to investigate the molecular basis of plant–pathogen interactions. The function of many potential virulence factors encoded in the Pst DC3000 genome and their modes of action are not fully understood. P. syringae is known to produce the exopolysaccharide alginate. Although AlgU, a sigma factor, is known to regulate the expression of genes such as algD related to alginate biosynthesis, the molecular mechanisms of AlgU in the virulence of Pst DC3000 is still unclear. To investigate the function of AlgU and alginate in plant–bacterial pathogen interactions, we generated ΔalgU and ΔalgD mutants. After inoculation with ΔalgU but not ΔalgD, host plants of Pst DC3000 including tomato and Arabidopsis had milder disease symptoms and reduced bacterial populations. Expression profiles of Pst DC3000 genes revealed that AlgU can regulate not only the expression of genes encoding alginate biosynthesis, but also the expression of genes related to type III effectors and the phytotoxin coronatine (COR). We also demonstrated that the ΔalgU mutant showed full virulence in the Arabidopsis fls2 efr1 double mutant, which is compromised in the recognition of PAMPs. Further, the application of COR was able to restore the phenotype of the ΔalgU mutant in the stomatal response. These results suggest that AlgU has an important role in the virulence of Pst DC3000 by regulating COR production.     

Current classification of Ralstonia solanacearum and genetic diversity of the strains in Japan

Ralstonia solanacearum is the causal organism of bacterial wilt of more than 200 species representing 50 families of plants in tropical, subtropical, and warm temperate regions in the world. Traditionally classified into five races based on differences in host range, R. solanacearum has also been grouped into six biovars on the basis of biochemical properties. With recent developments in molecular biology, various DNA-based analyses have been introduced and used to confirm that this binary system does not completely represent the diversity within R. solanacearum strains. Therefore, a new hierarchical classification scheme has been suggested, which defines R. solanacearum as a species complex and reorganized the concept of the species as a monophyletic cluster according to a phylogenetic analysis based on genomic sequence data. Here we discuss the current bacterial wilt situation and genetic relationships based on the recent classification system of Japanese R. solanacearum strains as well as worldwide strains. We also review the genetic, biochemical, and pathological characteristics of R. solanacearum strains, in particular, those affecting potato and Zingiberaceae plants as distinctly important pathogens in relation to continuously problematic and recent emergent diseases in Japan.     

Pathogenic characters of Japanese potato strains of Ralstonia solanacearum

Ralstonia solanacearum (Rs) strains in phylotypes I and IV isolated from potato in Japan were investigated for pathogenicity on potato, tomato, eggplant, Solanum integrifolium, tobacco, groundnut, and pumpkin. The strains were divided into 17 types based on differences in their pathogenicity on the tested plants. Particularly, the pathogenicity of most phylotype I strains on eggplant was distinctly different from that of the phylotype IV strains. When nine potato varieties (included two breeding lines) were inoculated with several Rs strains, phylotype IV strains were highly virulent on the breeding lines that are regarded as resistant to phylotype I strains.     

Lymphocyte blastogenic responses to inciting food allergens in dogs with food hypersensitivity

Lymphocyte blastogenic responses against food allergens in dogs with food hypersensitivity were evaluated in this study. Eleven dogs with food hypersensitivity, based on food elimination and oral food provocation tests and allergic responses to food allergens, were examined by various tests such as intradermal testing, antigen-specific IgE testing, and lymphocyte blastogenic responses. The number and kinds of food allergens identified as positive by these tests were compared with the offending food allergens that were found in an oral food provocation test. In 9 (82%) of the 11 dogs with food hypersensitivity, there was close agreement for positive allergens between the results of lymphocyte blastogenic responses and oral food provocation test; however, there was little agreement for intradermal and IgE testing of the positive allergens with those of the oral food provocation test (11% and 31%, respectively). In the 9 dogs, the stimulation indices of lymphocyte blastogenic responses increased to 2.0-10.1 upon food provocation but decreased significantly to 0.7-1.4 upon feeding the elimination diet until clinical signs disappeared. These results indicate that lymphocyte blastogenic responses may fluctuate because of exposure to offending food allergens in dogs with food hypersensitivity. Lymphocytes reactive to food allergens may play an important role in the pathogenesis of food hypersensitivity in dogs.