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
||Pseudomonas syringae pv. tomato and the
closely related pathovar P. s. pv. maculicola have been the
focus of intensive research in recent years, not only because of the
diseases they cause on tomato and crucifers, but because strains such as P.
s. pv. tomato DC3000 and P. s. pv. maculicola
ES4326 are pathogens of the model plant Arabidopsis thaliana.
Consequently, both P. s. pv. tomato and P. s. pv. maculicola
have been widely used to study the molecular mechanisms of host responses
to infection. Analyses of the molecular basis of pathogenesis in P. s.
pv. tomato reveal a complex and intimate interaction between
bacteria and plant cells that depends on the coordinated expres-sion of
multiple pathogenicity and virulence factors. These include toxins,
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 factors to parasitism and disease
development varies significantly between strains. Application of
functional genomics and cell biology to both pathogen and host within the P.
s. pv. tomato/ A. thaliana pathosystem provides a unique
opportunity to unravel the molecular interactions underlying plant
||Bacteria; Proteobacteria; gamma subdivision; Pseudomonadaceae/Moraxellaceae
group; Pseudomonadaceae family; Pseudomonas genus; Pseudomonas
syringae species; tomato pathovar.
||Gram-negative, aerobic, motile, rod-shaped, polar flagella,
oxidase negative, arginine dihydrolase negative, DNA 58-60 mol% GC,
elicits the hypersensitive response on tobacco.
||Primarily studied as the causal agent of bacterial speck of
tomato and as a model pathogen of A. thaliana, although it has been
isolated from a wide range of crop and weed species.
||Tomato ( Lycopersicon esculentum): Brown-black leaf
spots sometimes surrounded by chlorotic margin; dark superficial specks on
green fruit; specks on ripe fruit may become sunken, and are surrounded by
a zone of delayed ripening. Stunting and yield loss, particularly if young
plants are infected. Reduced market value of speckled fruit. A.
thaliana: Water-soaked, spreading lesions, sometimes surrounded by
||Seed borne. Survives as a saprophyte in plant debris, soil
and on leaf surfaces. Dispersed by aerosols and rain splash. Development
of disease symptoms favoured by leaf wetness and cool temperatures (55-77
°F/ 13-25 °C).
||Pathogen-free seed and transplants. Resistant and tolerant
cultivars. Sanitation, rotation, and drip irrigation to reduce leaf
wetness. Some measure of control with bactericides (copper, streptomycin).
Symptoms caused by P. s. pv. tomato DC3000 on tomato (L.
esculentum cv. Moneymaker) (left) and A. thaliana ecotype
Columbia (right) 7 days after spray inoculation.
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