Pseudomonas syringae: what it takes to be a pathogen

Pseudomonas syringaeuses a multitude of virulence factors to infect plants. In this Review, Xin and colleagues highlight key virulence strategies — immune suppression and water soaking — that allow this bacterium to become a successful pathogen under the right environmental conditions. Pseudomonas syringae is one of the best-studied plant pathogens and serves as a model for understanding host–microorganism interactions, bacterial virulence mechanisms and host adaptation of pathogens as well as microbial evolution, ecology and epidemiology. Comparative genomic studies have identified key genomic features that contribute to P. syringae virulence. P. syringae has evolved two main virulence strategies: suppression of host immunity and creation of an aqueous apoplast to form its niche in the phyllosphere. In addition, external environmental conditions such as humidity profoundly influence infection. P. syringae may serve as an excellent model to understand virulence and also of how pathogenic microorganisms integrate environmental conditions and plant microbiota to become ecologically robust and diverse pathogens of the plant kingdom.