The genetic characterization of Pseudomonas syringae pv. tagetis based on the 16S–23S rDNA intergenic spacer regions

Pseudomonas syringae pv. tagetis, a plant pathogen being considered as a biological control agent of Canada thistle (Cirsium arvense), produces tagetitoxin, an inhibitor of RNA polymerase which results in chlorosis of developing shoot tissues. Although the bacterium is known to affect several plant species in the Asteraceae and has been reported in several countries, little is known of its genetic diversity. The genetic relatedness of 24 strains of P. syringae pv. tagetis with respect to each other and to other P. syringae and Pseudomonas savastanoi pathovars was examined using 16S–23S rDNA intergenic spacer (ITS) sequence analysis. The size of the 16S–23S rDNA ITS regions ranged from 508 to 548 bp in length for all 17 P. syringae and P. savastanoi pathovars examined. The size of the 16S–23S rDNA ITS regions for all the P. syringae pv. helianthi and all the P. syringae pv. tagetis strains examined were 526 bp in length. Furthermore, the 16S–23S rDNA ITS regions of both P. syringae pv. tagetis and P. syringae pv. helianthi had DNA signatures at specific nucleotides that distinguished them from the 15 other P. syringae and P. savastanoi pathovars examined. These results provide strong evidence that P. syringae pv. helianthi is a nontoxigenic form of P. syringae pv. tagetis. The results also demonstrated that there is little genetic diversity among the known strains of P. syringae pv. tagetis. The genetic differences that do exist were not correlated with differences in host plant, geographical origin, or the ability to produce toxin.     

Cloning of genes required for hypersensitivity and pathogenicity inPseudomonas syringae pv.aptata

A genomic library ofPseudomonas syringae pv.aptata strain NCPPB 2664, which causes bacterial blight of sugar beet, lettuce and other plants, was constructed in the cosmid vector pCPP31. The 13.4 kbEcoRI fragment of the cosmid pHIR11, containing thehrp (hypersensitiveresponse andpathogenicity) gene cluster of the closely related bacteriumPseudomonas syringae pv.syringae strain 61, was used as a probe to identify a homologoushrp gene cluster inP. syringae pv.aptata. Thirty of 2500 cosmid clones, screened by colony hybridization, gave a strong hybridization signal with the probe, but none of these conferred to the non-pathogenic bacterium,Pseudomonas fluorescens, the ability to elicit the hypersensitive response (HR) in tobacco. Southern blot analysis ofEcoRI-digested genomic DNA ofP. syringae pv.aptata showed hybridizing bands of 12 kb and 4.4 kb. Only a 12 kb fragment hybridized in digests of the cosmids. Cosmid clone pCPP1069 was mutagenized with Tn10-minitet and marker-exchanged into the genome ofP. syringae pv.aptata. Three resulting prototrophic mutant strains failed to elicit the HR in tobacco and to cause disease in lettuce. The DNA flanking the Tn10-minitet insertions from mutated derivatives of pCPP1069 hybridized with the 10.6 kbBglII fragment of pHIR11. These results indicate thatP. syringae pv.aptata harbourshrp genes that are similar to, but arranged differently from, homologoushrp genes ofP. syringae pv.syringae.Abbreviations HR hypersensitive response - Hrp mutant unable to induce HR and pathogenicity - Psa Pseudomonas syringae pv.aptata - Pss Pseudomonas syringae pv.syringae - Ea Erwinia amylovora     

Construction of a Bacterial Artificial Chromosome Library and Characterization of hrp/hrc Gene Cluster of Pseudomonas Syringae Pathovar tagetis LMG5090

Pseudomonas syringae pv. tagetis causes apical chlorosis of several plant species in the Asteraceae, including marigold. As a means to facilitate the isolation of pathogenicity genes and to characterize the genome of this bacterium, we have constructed a bacterial artificial chromosome library of P. syringae pv. tagetis strain LMG5090. The library consists of 1,536 clones with insert size ranging from 30 to 160 kb and an average size of 86 kb. Based upon colony hybridization, the BAC clone 420E23 containing the hrp/hrc gene cluster encoding the type III secretion system was identified from this library and subsequently shotgun sequenced. The hrp/hrc gene cluster of P. syringae pv. tagetis has a 23 kb sequence which contains 27 open reading frames. Comparative analysis of the hrp/hrc gene cluster of P. syringae pv. tagetis LMG5090, P. syringae pv. tomato DC3000, P. syringae pv. syringae B728a, and P. syringae pv. phaseolicola 1448A revealed that the entire hrp/hrc gene cluster of P. syringae pv. tagetis is conserved and identically arranged in all four pathovars     

Comparative analysis of induction pattern of programmed cell death and defense-related responses during hypersensitive cell death and development of bacterial necrotic leaf spots in eggplant

Pseudomonas cichorii causes necrotic leaf spots (NLS), while Pseudomonas syringae pv. tabaci induces a hypersensitive response (HR) in eggplant. P. cichorii induced cell death at 9 h after inoculation (HAI), reaching a maximum of around 24–30 HAI. On the other hand, cell death was induced 6 HAI with P. syringae pv. tabaci, reaching a maximum of around 12–18 HAI. Superoxide generation was observed in eggplant inoculated with both bacteria. DNA fragmentation, cytochrome c release into the cytosol and expression of defense-related genes such as PR-1 and hsr203J was also induced by inoculation with both bacteria, but these plant reactions were more rapidly induced in eggplant inoculated with P. syringae pv. tabaci rather than those with P. cichorii. Lipid peroxidation and induction of lipoxygenase (LOX) was drastically induced in eggplant inoculated with P. syringae pv. tabaci compared to P. cichorii-inoculated eggplant. Pharmacological studies showed that induction of the cell death, and the NLS or the HR in response to both bacteria was commonly associated with de novo protein synthesis, reactive oxygen species and caspase III-like protease. Interestingly, involvement of lipid peroxidation, LOX, serine protease, and DNase differed between induction of NLS and HR. These results suggest that programmed cell death might be closely associated not only with the HR but also NLS. However, there may be differences not only in the induction kinetics and level of plant responses but also in the infection-related responses between HR and NLS.     

Gac two-component system in Pseudomonas syringae pv. tabaci is required for virulence but not for hypersensitive reaction

Pseudomonas syringae pv. tabaci 6605 causes wildfire disease on host tobacco plants. To investigate the regulatory mechanism of the expression of virulence, Gac two-component system-defective mutants, ΔgacA and ΔgacS, and a double mutant, ΔgacAΔgacS, were generated. These mutants produced smaller amounts of N-acyl homoserine lactones required for quorum sensing, had lost swarming motility, and had reduced expression of virulence-related hrp genes and the algT gene required for exopolysaccharide production. The ability of the mutants to cause disease symptoms in their host tobacco plant was remarkably reduced, while they retained the ability to induce hypersensitive reaction (HR) in the nonhost plants. These results indicated that the Gac two-component system of P. syringae pv. tabaci 6605 is indispensable for virulence on the host plant, but not for HR induction in the nonhost plants. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. The nucleotide sequence data reported in this paper have been submitted to the DDBJ/GenBank/EMBL databank with the accession numbers AB266103, AB266104, AB266105, AB266106, AB266107, AB266108.     

Identification and expression of the Pseudomonas syringae pv. aptata hrpZPsa gene which encodes an harpin elicitor

A sequence homologous to an internal fragment 0.75 kb BstXI of the Pseudomonas syringae pv. syringae hrpZ gene was identified in Pseudomonas syringae pv. aptata NCPPB 2664, the causal agent of bacterial blight in sugar beet, lettuce and other plants, and in E. coli DH10B (pCCP1069) containing the P. syringae pv. aptata hrp gene cluster. PCR with oligonucleotides, based on the hrpZ_Pss gene and used as primers with the total genomic DNA of P. syringae pv. aptata, amplified a 1 kb fragment that hybridized with the probe in highly stringent conditions. The amplicon was cloned into the pGEM-T® plasmid vector, amplified in E. coli DH5 and sequenced. The sequence showed 95%, 83% and 61% identity with those of hrpZ_Pss, hrpZ_Psg and hrpZ_Pst genes encoding the harpins of the P. syringae pv. syringae, glycinea and tomato, respectively. The amplicon was cloned into the pMAL® expression system. The expressed protein, fused with maltose-binding protein, was cleaved with a specific protease factor Xa, and purified using affinity chromatography. On the basis of the amino acid sequence and its ability to induce HR in tobacco leaves, it was identified as a P. syringae pv. aptata harpin.     

Early detection of bean infection by Pseudomonas syringae in asymptomatic leaf areas using chlorophyll fluorescence imaging

Chlorophyll fluorescence imaging has been used to analyse the response elicited in Phaseolus vulgaris after inoculation with Pseudomonas syringae pv. phaseolicola 1448A (compatible interaction) and P. syringae pv. tomato DC3000 (incompatible interaction). With the aim of modulating timing of symptom development, different cell densities were used to inoculate bean plants and the population dynamics of both bacterial strains was followed within the leaf tissue. Fluorescence quenching analysis was carried out and images of the different chlorophyll fluorescence parameters were obtained for infected as well as control plants at different timepoints post-infection. Among the different parameters analysed, we observed that non-photochemical quenching maximised the differences between the compatible and the incompatible interaction before the appearance of visual symptom. A decrease in non-photochemical quenching, evident in both infiltrated and non-infiltrated leaf areas, was observed in P. syringae pv. phaseolicola-infected plants as compared with corresponding values from controls and P. syringae pv. tomato-infected plants. No photoinhibitory damage was detected, as the maximum photosystem II quantum yield remained stable during the infection period analysed.     

A Phylogenomic Study of the OCTase Genes in Pseudomonas syringae Pathovars: The Horizontal Transfer of the argK–tox Cluster and the Evolutionary History of OCTase Genes on Their Genomes

Phytopathogenic Pseudomonas syringae is subdivided into about 50 pathovars due to their conspicuous differentiation with regard to pathogenicity. Based on the results of a phylogenetic analysis of four genes (gyrB, rpoD, hrpL, and hrpS), Sawada et al. (1999) showed that the ancestor of P. syringae had diverged into at least three monophyletic groups during its evolution. Physical maps of the genomes of representative strains of these three groups were constructed, which revealed that each strain had five rrn operons which existed on one circular genome. The fact that the structure and size of genomes vary greatly depending on the pathovar shows that P. syringae genomes are quite rich in plasticity and that they have undergone large-scale genomic rearrangements. Analyses of the codon usage and the GC content at the codon third position, in conjunction with phylogenomic analyses, showed that the gene cluster involved in phaseolotoxin synthesis (argK–tox cluster) expanded its distribution by conducting horizontal transfer onto the genomes of two P. syringae pathovars (pv. actinidiae and pv. phaseolicola) from bacterial species distantly related to P. syringae and that its acquisition was quite recent (i.e., after the ancestor of P. syringae diverged into the respective pathovars). Furthermore, the results of a detailed analysis of argK [an anabolic ornithine carbamoyltransferase (anabolic OCTase) gene], which is present within the argK–tox cluster, revealed the plausible process of generation of an unusual composition of the OCTase genes on the genomes of these two phaseolotoxin-producing pathovars: a catabolic OCTase gene (equivalent to the orthologue of arcB of P. aeruginosa) and an anabolic OCTase gene (argF), which must have been formed by gene duplication, have first been present on the genome of the ancestor of P. syringae; the catabolic OCTase gene has been deleted; the ancestor has diverged into the respective pathovars; the foreign-originated argK–tox cluster has horizontally transferred onto the genomes of pv. actinidiae and pv. phaseolicola; and hence two copies of only the anabolic OCTase genes (argK and argF) came to exist on the genomes of these two pathovars. Thus, the horizontal gene transfer and the genomic rearrangement were proven to have played an important role in the pathogenic differentiation and diversification of P. syringae. Received: 22 May 2001 / Accepted: 26 September 2001     

Distribution of some virulence related-properties of Vibrioalginolyticus strains isolated from Mediterranean seawater (Bay of Khenis, Tunisia): investigation of eight Vibriocholerae virulence genes

This study characterizes 28 Vibrio alginolyticus strains isolated from seawater from the Seacoast of Monastir (Khenis; Tunisia). V. alginolyticus were isolated using the TCBS modified agar plates and the biochemical activities were tested using RapID NF plus Strips. Proteases activities, hemolysis, antibiotics susceptibility, and adhesion to fish mucus and epithelial cell lines (Hep-2 and Caco-2) were also investigated. Eight Vibrio cholerae virulence genes (toxR, toxS, toxRS, toxT, ctxA, vpi, ace, zot) were investigated by PCR in genomes of V. alginolyticus strains. Most of the studied strains were β-haemolytic and produce many proteolytic enzymes. All isolates described here were resistant to several antibiotics tested. Six strains were able to adhere strongly to both Hep-2 and Caco-2 cell lines. The PCR investigation of V. cholerae genes showed a large distribution among the genomes of all V. alginolyticus strains. The toxR operon was found in 9 V. alginolyticus strains out of 28 studied. Only one strain was positive for the toxS and toxRS respectively. Five strains showed a positive amplification for the virulence pathogenic island (vpi), seven for the toxT, 3 for the ctxA and 9 for the Zonula occludens toxin (zot). The bay of Khenis harbors different genotypes of V. alginolyticus strains who inheritated several virulence genes from autochthones bacteria such as V. cholerae. These strains were able to produce several virulence enzymes and exhibit a high power to adhere to human epithelial cells and fish mucus.     

The Serological Heterogeneity of Pseudomonas syringae pv. atrofaciens Strains and Their Ecological Niches

The paper deals with a comparative analysis of the serological and ecological properties of Pseudomonas syringae pv. atrofaciens strains from the collections of microbial cultures at the Malkov Institute for Plant Genetic Resources and Zabolotny Institute of Microbiology and Virology. All of the strains from the Bulgarian collection, except for one, fall into five serogroups (II through VI) of the classification system of Pastushenko and Simonovich. The P. syringae pv. atrofaciens strains isolated from Bulgarian and Ukrainian wheats belong mainly to serogroups II and IV, respectively. The strains that were isolated from rye plants belong to serogroup I. The strains isolated from sorghum and Sudan grass belong to serogroups II, IV, and VI. Serogroup III includes the P. syringae pv. atrofaciens strains that were isolated from cereals in the United Kingdom but not in Ukraine.     

Phylogenetic Analysis of Pseudomonas syringae Pathovars Suggests the Horizontal Gene Transfer of argK and the Evolutionary Stability of hrp Gene Cluster

Pseudomonas syringae are differentiated into approximately 50 pathovars with different plant pathogenicities and host specificities. To understand its pathogenicity differentiation and the evolutionary mechanisms of pathogenicity-related genes, phylogenetic analyses were conducted using 56 strains belonging to 19 pathovars. gyrB and rpoD were adopted as the index genes to determine the course of bacterial genome evolution, and hrpL and hrpS were selected as the representatives of the pathogenicity-related genes located on the genome (chromosome). Based on these data, NJ, MP, and ML phylogenetic trees were constructed, and thus 3 trees for each gene and 12 gene trees in total were obtained, all of which showed three distinct monophyletic groups: Groups 1, 2 and 3. The observation that the same set of OTUs constitute each group in all four genes suggests that these genes had not experienced any intergroup horizontal gene transfer within P. syringae but have been stable on and evolved along with the P. syringae genome. These four index genes were then compared with another pathogenicity-related gene, argK (the phaseolotoxin-resistant ornithine carbamoyltransferase gene, which exists within the argK–tox gene cluster). All 13 strains of pv. phaseolicola and pv. actinidiae used had been confirmed to produce phaseolotoxin and to have argK, whose sequences were completely identical, without a single synonymous substitution among the strains used (Sawada et al. 1997a). On the other hand, argK were not present on the genomes of the other 43 strains used other than pv. actinidiae and pv. phaseolicola. Thus, the productivity of phaseolotoxin and the possession of the argK gene were shown at only two points on the phylogenetic tree: Group 1 (pv. actinidiae) and Group 3 (pv. phaseolicola). A t test between these two pathovars for the synonymous distances of argK and the tandemly combined sequence of the four index genes showed a high significance, suggesting that the argK gene (or argK–tox gene cluster) experienced horizontal gene transfer and expanded its distribution over two pathovars after the pathovars had separated, thus showing a base substitution pattern extremely different from that of the noncluster region of the genome. Received: 18 January 1999 / Accepted: 25 May 1999     

New disease resistance genes in soybean against Pseudomonas syringae pv glycinea: evidence that one of them interacts with a bacterial elicitor

Summary Soybean [Glycine max (L.) Merr.] cultivars Flambeau and Merit differed in their resistance to Pseudomonas syringae pv glycinea (Psg) race 4, carrying each of four different avirulence (avr) genes cloned from Psg or the related bacterium, Pseudomonas syringae pv tomato. Segregation data for F₂ and F₃ progeny of Flambeau x Merit crosses indicated that single dominant and nonallelic genes account for resistance to Psg race 4, carrying avirulence genes avrA, avrB, avrC, or avrD. Segregants were also recovered that carried all four or none of the disease resistance genes. One of the disease resistance genes (Rpg1, complementing bacterial avirulence gene B) had been described previously, but the other three genes — designated Rpg2, Rpg3, and Rpg4 — had not here to fore been defined. Rpg3 and Rpg4 are linked (40.5 ± 3.2 recombination units). Rpg4 complements avrD, cloned from Pseudomonas syringae pv tomato, but a functional copy of this avirulence gene has not thus far been observed in Pseudomonas syringae pv glycinea. Resistance gene Rpg4 therefore may account in part for the resistance of soybean to Pseudomonas syringae pv tomato and other pathogens harboring avrD.     

Phylogeography of the endemic St. Lucia whiptail lizard Cnemidophorus vanzoi: Conservation genetics at the species boundary

Vicariance and isolation leading to speciation of reptiles on islands is well exemplified in a number of taxa in the Caribbean. The St. Lucia whiptail (Cnemidophorus vanzoi), considered a single species, is found on two small islets (Maria Major and Maria Minor) off the main island of St. Lucia. From lizards collected from both localities, we gathered morphological measurements and analysed the genetic divergence between populations, using a molecular survey of ∼ ∼2800 mtDNA base pairs and 8 microsatellites. There are significant differences in body size and general form and fixed but small mtDNA differences between island populations. Microsatellites reveal low diversity within populations but very high differentiation between islands with non-overlapping allele size ranges at all except one microsatellite and two loci exhibiting single-base polymorphism, fixed between islands. Based on these results, we examine published criteria to determine whether the studied island forms could be considered true species. According to the phylogenetic species concept and Moritz’s evolutionary significant unit (ESU) criteria, the two lizard populations can be considered separate entities. Crandall et al.’s (2000, Trends Ecol. Evol., 15, 290–295) broader categorization of population distinctiveness, based on concepts of ecological and genetic exchangeability, produces conflicting results depending on the interpretation of the observed ecological data. Following Fraser and Bernatchez’s (2001, Mol. Ecol., 10, 2741–2752) framework for management decisions when ecological data are not sufficient we propose that the lizard populations on the Maria islands are on differing evolutionary trajectories and thus at the species boundary. The populations are of high priority to conservation, thus meriting separate management.     

Negative regulation of pathogenesis in <Emphasis Type="Italic">Pseudomonas syringae</Emphasis> pv. <Emphasis Type="Italic">tabaci</Emphasis> 11528 by ATP-dependent lon protease

Pseudomonas syringae pv. tabaci causes wildfire disease in tobacco plants. The hrp pathogenicity island (hrp PAI) of P. syringae pv. tabaci encodes a type III secretion system (TTSS) and its regulatory system, which are required for pathogenesis in plants. Three important regulatory proteins-HrpR, HrpS, and HrpL-have been identified to activate hrp PAI gene expression. The bacterial Lon protease regulates the expression of various genes. To investigate the regulatory mechanism of the Lon protease in P. syringae pv. tabaci 11528, we cloned the lon gene, and then a Δlon mutant was generated by allelic exchange. lon mutants showed increased UV sensitivity, which is a typical feature of such mutants. The Δlon mutant produced higher levels of tabtoxin than the wild-type. The lacZ gene was fused with hrpA promoter and activity of β-galactosidase was measured in hrp-repressing and hrp-inducing media. The Lon protease functioned as a negative regulator of hrp PAI under hrp-repressing conditions. We found that strains with lon disruption elicited the host defense system more rapidly and strongly than the wild-type strain, suggesting that the Lon protease is essential for systemic pathogenesis.     

Insight into Types I and II nonhost resistance using expression patterns of defense-related genes in tobacco

Plants protect themselves against pathogens using a range of response mechanisms. There are two categories of nonhost resistance: Type I, which does not result in visible cell death; and Type II, which entails localized programmed cell death (or hypersensitive response) in response to nonhost pathogens. The genes responsible for these two systems have not yet been intensively investigated at the molecular level. Using tobacco plants (Nicotiana tabacum), we compared expression of 12 defense-related genes between a Type I (Xanthomonas axonopodis pv. glycines 8ra) nonhost interaction, and two Type II (Pseudomonas syringae pv. syringae 61 and P. syringae pv. phaseolicola NPS3121) nonhost interactions, as well as those expressed during R gene-mediated resistance to Tobacco mosaic virus. In general, expression of most defense-related genes during R gene-mediated resistance was activated 48 h after challenge by TMV; the same genes were upregulated as early as 9 h after infiltration by nonhost pathogens. Surprisingly, X. axonopodis pv. glycines (Type I) elicited the same set of defense-related genes as did two pathovars of P. syringae, despite the absence of visible cell death. In two examples of Type II nonhost interactions, P. syringae pv. phaseolicola NPS3121 produced an expression profile more closely resembling that of X. axonopodis pv. glycines 8ra, than that of P. syringae pv. syringae 61. These results suggest that Type I nonhost resistance may act as a mechanism providing a more specific and active defense response against a broad range of potential pathogens.     

Accumulation of gentisic acid as associated with systemic infections but not with the hypersensitive response in plant-pathogen interactions

In the present work we have studied the accumulation of gentisic acid (2,5-dihydroxybenzoic acid, a metabolic derivative of salicylic acid, SA) in the plant-pathogen systems, Cucumis sativus and Gynura aurantiaca, infected with either prunus necrotic ringspot virus (PNRSV) or the exocortis viroid (CEVd), respectively. Both pathogens produced systemic infections and accumulated large amounts of the intermediary signal molecule gentisic acid as ascertained by electrospray ionization mass spectrometry (ESI-MS) coupled on line with high performance liquid chromatography (HPLC). The compound was found mostly in a conjugated (β-glucoside) form. Gentisic acid has also been found to accumulate (although at lower levels) in cucumber inoculated with low doses of Pseudomonas syringae pv. tomato, producing a nonnecrotic reaction. In contrast, when cucumber was inoculated with high doses of this pathogen, a hypersensitive reaction occurred, but no gentisic-acid signal was induced. This is consistent with our results supporting the idea that gentisic-acid signaling may be restricted to nonnecrotizing reactions of the host plant (Bellés et al. in Mol Plant-Microbe Interact 12:227–235, 1999). In cucumber and Gynura plants, the activity of gentisic acid as inducing signal was different to that of SA, thus confirming the data found for tomato. Exogenously supplied gentisic acid was able to induce peroxidase activity in both Gynura and cucumber plants in a similar way as SA or pathogens. However, gentisic-acid treatments strongly induced polyphenol oxidase activity in cucumber, whereas pathogen infection or SA treatment resulted in a lower induction of this enzyme. Nevertheless, gentisic acid did not induce other defensive proteins which are induced by SA in these plants. This indicates that gentisic acid could act as an additional signal to SA for the activation of plant defenses in cucumber and Gynura plants.     

Karyotype analysis and physical mapping of 45S rDNA in eight species of Sophora, Robinia , and Amorpha

The karyotype analysis and physical locations of 45S rDNA were carried out by means of fluorescence in situ hybridization in three species, and two forms of Sophora, two species of Robina, and one species of Amorpha. S. japonica L., S. japonica L. f. oligophylla Franch., S. japonica L. f. pendula Loud., and S. xanthantha C. Y. Ma. are all tetraploids with 2n = 28. There were four 45S rDNA sites in pericentromeric regions of two pairs of chromosomes in each of them. S. rubriflora Tsoong. is a triploid with 2n = 21, and three sites were located in each satellite of group 5 chromosomes. In R. pseudoacacia L. (2n = 2x = 22), we examined four intensive signals in telomeric regions of two pairs of satellite chromosomes. In R. hispida L. (2n = 2x = 30), there were four other signals in centromeric regions besides those like in R. pseudoacacia. Amorpha fruticosa L. has most chromosomes (2n = 40) among the eight materials, however, there were only six 45S rDNA loci and they laid in centromeric regions, and satellites of three pairs of chromosomes. 45S rDNA is a valuable chromosomal landmark in karyotype analysis. The distribution and genomic organization of rDNA in the three genera were also discussed. __________ Translated from Acta Botanica Yunnanica, 2005, 27(3): 261–268 [译自: 云南植物研究, 2005, 27(3): 261–268]     

Promoter activation of pepper class II basic chitinase gene, CAChi2, and enhanced bacterial disease resistance and osmotic stress tolerance in the CAChi2-overexpressing Arabidopsis

The activation of the CAChi2 promoter as the result of bacterial infection and osmotic stresses was examined using the Agrobacterium-mediated transient expression assay. Several stress-related cis-acting elements were revealed within the upstream genomic sequence of the CAChi2 gene. In tobacco leaf tissues transiently transformed with the CAChi2 promoter-β-glucuronidase (GUS) gene, the CAChi2 promoter was up-regulated by Pseudomonas syringae pv. tabaci infection. The CAChi2-GUS activation was closely related to osmotic stresses, including treatment with mannitol and NaCl. The −378 CAChi2 promoter was sufficient for the CAChi2 gene induction by salicylic acid treatment. CAChi2 overexpression in the transgenic Arabidopsis plants enhanced bacterial disease resistance against Pseudomonas syringae pv. tomato infection. CAChi2-overexpressing Arabidopsis plants also exhibited increased tolerance to NaCl-induced osmotic stresses during seed germination and seedling growth. CAChi2 overexpression induced the expression of the NaCl stress-responsive gene RD29A in the absence of NaCl stress. The CAChi2-overexpressing transgenic plants exhibited increased sensitivity to abscisic acid during seed germination. The nucleotide sequence data reported here has been deposited in the GenBank database under the accession number AY775335.     

Comment arising from a paper by Wittmer et al.: hypothesis testing for top-down and bottom-up effects in woodland caribou population dynamics

Conservation strategies for populations of woodland caribou Rangifer tarandus caribou frequently emphasize the importance of predator–prey relationships and the availability of lichen-rich late seral forests, yet the importance of summer diet and forage availability to woodland caribou survival is poorly understood. In a recent article, Wittmer et al. (Can J Zool 83:407–418, 2005b) concluded that woodland caribou in British Columbia were declining as a consequence of increased predation that was facilitated by habitat alteration. Their conclusion is consistent with the findings of other authors who have suggested that predation is the most important proximal factor limiting woodland caribou populations (Bergerud and Elliot in Can J Zool 64:1515–1529, 1986; Edmonds in Can J Zool 66:817–826, 1988; Rettie and Messier in Can J Zool 76:251–259, 1998; Hayes et al. in Wildl Monogr 152:1–35, 2003). Wittmer et al. (Can J Zool 83:407–418, 2005b) presented three alternative, contrasting hypotheses for caribou decline that differed in terms of predicted differences in instantaneous rates of increase, pregnancy rates, causes of mortality, and seasonal vulnerability to mortality (Table 1, p 258). These authors rejected the hypotheses that food or an interaction between food and predation was responsible for observed declines in caribou populations; however, the use of pregnancy rate, mortality season and cause of mortality to contrast the alternative hypotheses is problematic. We argue here that the data employed in their study were insufficient to properly evaluate a predation-sensitive foraging hypothesis for caribou decline. Empirical data on seasonal forage availability and quality and plane of nutrition of caribou would be required to test the competing hypotheses. We suggest that methodological limitations in studies of woodland caribou population dynamics prohibit proper evaluation of the mechanism of caribou population declines and fail to elucidate potential interactions between top-down and bottom-up effects on populations. An erratum to this article can be found at     

In vitro culture response of common bean explants to filtrate from Pseudomonas syringae pv. Phaseolicola and correlation with disease resistance

Summary The in vitro culture responses from different explants of a race-specific resistant cultivar (Red Mexican) and a racesusceptible cultivar (Palme?a) to halo-blight pathogen (Pseudomonas syringae pv. phaseolicola were studied. Two kinds of filtrate obtained from a phaseolotoxin producer wild type and a non-producer mutant of P. syringae pv. phaseolicola race-7 were used. Callus formation of Red Mexican was significantly reduced in the presence of phaseolotoxin. Bud-shoot growth was more sensitive than callus formation to other metabolites present in the pathogen filtrate, but the presence of phaseolotoxin in the media showed a positive correlation between resistance to halo blight race-7 pathogen and bud-shoot growth. Our results indicate that differential in vitro responses are influenced by the plant genotype and by the metabolite composition and concentration of the filtrate.