Blackwell Science, Ltd PATHOGEN ... - …

1 MOLECULAR PLANT PATHOLOGY (2000) 1 (5), 263 275 2000 Blackwell SCIENCE LTD 263 Blackwell Science, Ltd PATHOGEN PROFILE pseudomonas syringae pv. tomato : the right PATHOGEN , of the right plant, at the right time GAIL M. PRESTON Department of Plant Sciences, University of Oxford, South Parks Road, Oxford, OX1 3RB, UK SUMMARY pseudomonas syringae pv. tomato and the closely relatedpathovar P. s. pv. maculicola have been the focus of intensiveresearch in recent years, not only because of the diseases theycause on tomato and crucifers, but because strains such as P.

2 S. pv. tomato DC3000 and P. s. pv. maculicola ES4326 are pathogensof the model plant Arabidopsis thaliana . Consequently, both P. s. pv. tomato and P. s. pv. maculicola have been widely usedto study the molecular mechanisms of host responses to of the molecular basis of pathogenesis in P. s. pv. tomato reveal a complex and intimate interaction betweenbacteria and plant cells that depends on the coordinated expres-sion of multiple pathogenicity and virulence factors.

3 These includetoxins, extracellular proteins and polysaccharides, and the trans-location of proteins into plant cells by the type III (Hrp)secretion system. The contribution of individual virulence factorsto parasitism and disease development varies significantlybetween strains. Application of functional genomics and cellbiology to both PATHOGEN and host within the P. s. pv. tomato / A. thaliana pathosystem provides a unique opportunity to unravelthe molecular interactions underlying plant pathogenesis.

4 Taxonomic relationship: Bacteria; Proteobacteria; gammasubdivision; Pseudomonadaceae/Moraxellaceae group; Pseu - domonadaceae family; pseudomonas genus; Pseudomonassyringae species; tomato pathovar. Microbiological properties: Gram-negative, aerobic, motile,rod-shaped, polar flagella, oxidase negative, arginine dihydrolasenegative, DNA 58 60 mol% GC, elicits the hypersensitive responseon tobacco. Host range: Primarily studied as the causal agent of bacterialspeck of tomato and as a model PATHOGEN of A.

5 Thaliana , althoughit has been isolated from a wide range of crop and weed species. Disease symptoms: Tomato ( Lycopersicon esculentum ): Brown-black leaf spots sometimes surrounded by chlorotic margin; darksuperficial specks on green fruit; specks on ripe fruit may becomesunken, and are surrounded by a zone of delayed and yield loss, particularly if young plants are market value of speckled fruit. A. thaliana : Water-soaked,spreading lesions, sometimes surrounded by chlorotic margin. Epidemiology: Seed borne.

6 Survives as a saprophyte in plantdebris, soil and on leaf surfaces. Dispersed by aerosols and rainsplash. Development of disease symptoms favoured by leaf wetnessand cool temperatures (55 77 F / 13 25 C). Disease control: PATHOGEN -free seed and transplants. Resistantand tolerant cultivars. Sanitation, rotation, and drip irrigation toreduce leaf wetness. Some measure of control with bactericides (copper, streptomycin). INTRODUCTION pseudomonas syringae pv. tomato is the causal agent of bacterialspeck of tomato.

7 Like many syringae pathovars it is found growingepiphytically on a wide range of plants, although field popula-tions decline in the absence of a susceptible host. Serious diseaseoutbreaks are relatively infrequent, and are favoured by highleaf wetness, cool temperatures and cultural practices that allowbacteria to be disseminated between host plants. There arethree main reasons for the high level of scientific interest in thispathogen. Firstly, as an easily cultured Gram-negative bacterialpathogen it is amenable to a wide range of molecular geneticand cell biology techniques, facilitating the experimentalidentification and manipulation of putative pathogenicity andvirulence factors.

8 Second, tomato ( Lycopersicon esculentum )is similarly amenable to transformation and genetic analysis,facilitating the isolation and characterization of plant genesinvolved in host responses. But third, and perhaps most signific-antly, many strains of P. s. pv. tomato and the closely relatedpathogen P. s. pv. maculicola are pathogenic on the model plant * Correspondence : Dr Gail M. Preston, Department of Plant Sciences, University ofOxford, South Parks Road, Oxford, OX1 3RB, UK.

9 E-mail: Page 263 Wednesday, November 1, 2000 5:04 PM 264 G. M. PRESTON MOLECULAR PLANT PATHOLOGY (2000) 1 (5), 263 275 2000 Blackwell SCIENCE LTD Arabidopsis thaliana , and certain strains exhibit race-cultivarspecificity on this host, thus providing a model pathosystemfor studying both compatible and incompatible host A. thaliana and P. s. pv. tomato are currently the subjectsof comprehensive genomic and functional genomic analyses thatcould greatly increase our understanding of bacterial pathogenesisand plant responses to bacterial infection.

10 It is time to reviewthe biology of P. s. pv. tomato and to consider how current advancesin genomics, proteomics and cell biology can be most profitablyapplied to advance our understanding of this model PATHOGEN . P. S. PV. TOMATO AND P. S. PV. MACULICOLA ARE MEMBERS OF P. SYRINAGE GENOSPECIES III AND CAUSE DISEASES OF TOMATOES AND CRUCIFERS P. s. pvs. tomato and maculicola have been shown by DNA pairinganalyses to belong to the same genomic species P. syringae genospecies III.