absence of the Rcr3 pathogenicity target. The characterization of a Cf0/rcr3 mutant will reveal whether Rcr3 is necessary for full pathogenicity of C. fulvum.

The Guard hypothesis predicts that for each R protein there is both a corresponding pathogen Avr product and a host target. Such a model would explain the dual recognition capacity of some NB-LRR proteins such as RPM1 and Mi-1 if they “guard” the same host component targeted by unrelated Avr products. Evolutionary mechanisms sustaining R gene diversity are essential for the plant to be able to detect distinct pathogen (a)virulence products that target R protein-“guarded ” host components.

All members of the Jones lab are thanked for useful discussion. We thank Sara Perkins, Margaret Shailer, and Justine Campling for their excellent horticultural service. This work was supported in part by the United Kingdom Biotechnology and Biological Sciences Research Council (M.S.D.) and by a Gatsby Ph.D. studentship (C.G.). The Sainsbury Laboratory is supported by the Gatsby Charitable Foundation.

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Front Matter (R1-R5)

Pathogens and Host: The Dance is the Same, the Couples are Different (1-2)

Striking a Balance: Modulation of the Actin Cytoskeleton by Salmonella (3-10)

Structure and Function of Pectic Enzymes: Virulence Factors of Plant Pathogens (11-18)

Pseudomonas syringae Hrp Type III Secretion System and Effector Proteins (19-26)

Molecular and Cell Biology Aspects of Plague (27-32)

A Framework for Interpreting the Leucine-rich Repeats of the Listeria Internalins (33-37)

Acyl-homoserine Lactone Quorum Sensing in Gram-negative Bacteria: A Signaling Mechanism Involved in Associations with Higher Organisms (38-42)

Phenotypic Variation and Intracellular Parasitism by Histoplasma capsulatum (43-47)

Exploitation of Host Cells by Enteropathogenic Escherichia coli (48-55)

Genetic Complexity of Pathogen Perception by Plants: The Example of Rcr3, a Tomato Gene Required Specifically by Cf-2 (56-63)

Plants and Animals Share Functionally Common Bacterial Virulence Factors (64-70)

Role of the Cystic Fibrosis Transmembrane Conductance Regulator in Innate Immunity to Pseudomonas aeruginosa Infections (71-77)

Bad Bugs and Beleaguered Bladders: Interplay Between Uropathogenic Escherichia coli and Innate Host Defenses (78-84)

AvrPto-dependent Pto-interacting Proteins and AvrPto-interacting Proteins in Tomato (85-89)

Reactive Oxygen and Nitrogen Intermediates in the Relationship Between Mammalian Hosts and Microbial Pathogens (90-97)

Nitric Oxide and Salicylic Acid Signaling in Plant Defense (98-104)

The Role of Antimicrobial Peptides in Animal Defenses (105-110)

Suramin Inhibits Initiation of Defense Signaling by Systemin, Chitosan, and a ß-glucan Elicitor in Suspension-cultured Lycopersicon Peruvianum Cells (111-116)