The bacterial family Enterobacteriaceae is notable for its well studied human pathogens, including Salmonella, Yersinia, Shigella, and Escherichia spp. However, it also contains several plant pathogens. We report the genome sequence of a plant pathogenic enterobacterium, Erwinia carotovora subsp. atroseptica (Eca) strain SCRI1043, the causative agent of soft rot and blackleg potato diseases. Approximately 33% of Eca genes are not shared with sequenced enterobacterial human pathogens, including some predicted to facilitate unexpected metabolic traits, such as nitrogen fixation and opine catabolism. This proportion of genes also contains an overrepresentation of pathogenicity determinants, including possible horizontally acquired gene clusters for putative type IV secretion and polyketide phytotoxin synthesis. To investigate whether these gene clusters play a role in the disease process, an arrayed set of insertional mutants was generated, and mutations were identified. Plant bioassays showed that these mutants were significantly reduced in virulence, demonstrating both the presence of novel pathogenicity determinants in Eca, and the impact of functional genomics in expanding our understanding of phytopathogenicity in the Enterobacteriaceae.

SUMMARYThe soft rot erwiniae, Erwinia carotovora ssp. atroseptica ( Eca ) , E. carotovora ssp. carotovora ( Ecc ) and E. chrysanthemi ( Ech ) are major bacterial pathogens of potato and other crops world-wide. We currently understand much about how these bacteria attack plants and protect themselves against plant defences. However, the processes underlying the establishment of infection, differences in host range and their ability to survive when not causing disease, largely remain a mystery. This review will focus on our current knowledge of pathogenesis in these organisms and discuss how modern genomic approaches, including complete genome sequencing of Eca and Ech , may open the door to a new understanding of the potential subtlety and complexity of soft rot erwiniae and their interactions with plants.Taxonomy : The soft rot erwiniae are members of the Enterobacteriaceae , along with other plant pathogens such as Erwinia amylovora and human pathogens such as Escherichia coli , Salmonella spp. and Yersinia spp. Although the genus name Erwinia is most often used to describe the group, an alternative genus name Pectobacterium was recently proposed for the soft rot species.Host Range: Ech mainly affects crops and other plants in tropical and subtropical regions and has a wide host range that includes potato and the important model host African violet ( Saintpaulia ionantha ). Ecc affects crops and other plants in subtropical and temperate regions and has probably the widest host range, which also includes potato. Eca , on the other hand, has a host range limited almost exclusively to potato in temperate regions only.Disease Symptoms: Soft rot erwiniae cause general tissue maceration, termed soft rot disease, through the production of plant cell wall degrading enzymes. Environmental factors such as temperature, low oxygen concentration and free water play an essential role in disease development. On potato, and possibly other plants, disease symptoms may differ, e.g. blackleg disease is associated more with Eca and Ech than with Ecc.Useful Websites: http://www.scri.sari.ac.uk/TiPP/Erwinia.htm, http://www.ahabs.wisc.edu:16080/ ∼ pernalab/erwinia/index.htm, http://www.tigr.org/tdb/mdb/mdbinprogress.html, http://www.sanger.ac.uk/Projects/E_carotovora/. INTRODUCTIONThe soft rot erwiniae are pathogens of many plant species, affecting crops in temperate to tropical regions world-wide. Eca has a narrow host range restricted almost exclusively to potato in temperate regions. Ech is more frequent in subtropical and tropical climates and has a host range that includes carnation, leopold lily, maize, pineapple, potato and African violet ( Saintpaulia ionantha ), the latter of which has been used extensively as a model system for research. Ech also causes disease on certain crops and other plants in temperate regions, e.g. dahlia and potato. Ecc mainly affects crops in subtropical and temperate regions and has probably the widest host range, including Brussels sprout, carrot, celery, cucumber, capsicum, turnip, chicory and po...

SummaryA diverse range of plant proteases are implicated in pathogen perception and in subsequent signalling and execution of disease resistance. We demonstrate, using protease inhibitors and virus-induced gene silencing (VIGS), that the plant papain cysteine protease cathepsin B is required for the disease resistance hypersensitive response (HR). VIGS of cathepsin B prevented programmed cell death (PCD) and compromised disease resistance induced by two distinct non-host bacterial pathogens. It also suppressed the HR triggered by transient co-expression of potato R3a and Phytophthora infestans Avr3a genes. However, VIGS of cathepsin B did not compromise HR following recognition of Cladosporium fulvum AVR4 by tomato Cf-4, indicating that plant PCD can be independent of cathepsin B. The non-host HR to Erwinia amylovora was accompanied by a transient increase in cathepsin B transcript level and enzymatic activity and induction of the HR marker gene Hsr203. VIGS of cathepsin B significantly reduced the induction of Hsr203 following E. amylovora challenge, further demonstrating a role for this protease in PCD. Whereas cathepsin B is often relocalized from the lysosome to the cytosol during animal PCD, plant cathepsin B is secreted into the apoplast, and is activated upon secretion in the absence of pathogen challenge.

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Dickeya dadantii is a plant-pathogenic enterobacterium responsible for the soft rot disease of many plants of economic importance. We present here the sequence of strain 3937, a strain widely used as a model system for research on the molecular biology and pathogenicity of this group of bacteria. Dickeya dadantii, formerly Erwinia chrysanthemi (11), is the causative agent of soft rot disease in a wide range of plant species, including many economically important crops (10). Soft rot results from the maceration of plant tissues following degradation of pectin, the major component of primary cell walls (7). D. dadantii is a devastating opportunistic pathogen in storage organs and fleshy tissues, particularly when compromised by bruising, excess water, low oxygen levels, or high temperatures. D. dadantii is also associated with systemic infections, vascular disorders, foliar necroses, and latent infections in growing plants. We sequenced and annotated the complete genome of Dickeya dadantii strain 3937, a strain widely used as a model system for research on the molecular biology and pathogenicity of this group of bacteria. Two whole-genome shotgun libraries were prepared with plasmid pHOS2 with target insert sizes of 2 to 3 kb and 10 to 12 kb. We collected approximately 67,000 dual-end sequences, 67% from small-insert clones and 33% from the larger insert library. Sequences were assembled into contigs using the Celera assembler (9), and this assembly was transferred to SeqMan II (Lasergene) for finishing. Primer walking was employed to close gaps covered by clones available from the shotgun libraries. The remaining gaps were closed by sequencing PCR products generated using primers designed from the ends of assembled and ordered contigs. PCR products spanning each rRNA operon were sequenced separately to resolve sequence differences between copies. We used Glimmer 2.0 (3) for initial prediction of protein coding regions. We added, deleted, and revised endpoints of genes based on comparisons to other genomes, genes, and proteins in the NCBI databases. tRNA sequences were identified using tRNAscan-SE (8) with additional examination to identify specific tRNAs not distinguishable by their anticodons alone. rRNA genes were identified by comparison to other enterobacterial sequences using