Decreased abundance of type III secretion system-inducing signals in Arabidopsis mkp1 enhances resistance against Pseudomonas syringae

• Published in: Proceedings of the National Academy of Sciences - PNAS 2014-05, Vol.111 (18), p.6846-6851
• Main Authors: Anderson, Jeffrey C., Wan, Ying, Kim, Young-Mo, Pasa-Tolic, Ljiljana, Metz, Thomas O., Peck, Scott C.
• Format: Article
• Language: English
• Subjects: Arabidopsis; Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis - microbiology; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Bacteria; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Biological activity; Biological Sciences; Drug resistance; Gene expression regulation; Genes, Plant; Genotype & phenotype; Gram-negative bacteria; Host-Pathogen Interactions - genetics; Host-Pathogen Interactions - physiology; Infections; Lycopersicon esculentum; Metabolites; Metabolomics; Mitogen-Activated Protein Kinases - genetics; Mitogen-Activated Protein Kinases - metabolism; Mutation; Pathogens; Plant Diseases - microbiology; Plants; Protein Tyrosine Phosphatases; Pseudomonas syringae; Pseudomonas syringae - genetics; Pseudomonas syringae - metabolism; Pseudomonas syringae - pathogenicity; Receptors, Pattern Recognition - metabolism; Secretion; Signal transduction; Virulence; Virulence - genetics; Virulence - physiology
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1403248111

Genes encoding the virulence-promoting type III secretion system (T3SS) in phytopathogenic bacteria are induced at the start of infection, indicating that recognition of signals from the host plant initiates this response. However, the precise nature of these signals and whether their concentrations can be altered to affect the biological outcome of host–pathogen interactions remain speculative. Here we use a metabolomic comparison of resistant and susceptible genotypes to identify plant-derived metabolites that induce T3SS genes in Pseudomonas syringae pv tomato DC3000 and report that mapk phosphatase 1 (mkp1), an Arabidopsis mutant that is more resistant to bacterial infection, produces decreased levels of these bioactive compounds. Consistent with these observations, T3SS effector expression and delivery by DC3000 was impaired when infecting the mkp1 mutant. The addition of bioactive metabolites fully restored T3SS effector delivery and suppressed the enhanced resistance in the mkp1 mutant. Pretreatment of plants with pathogen-associated molecular patterns (PAMPs) to induce PAMP-triggered immunity (PTI) also restricts T3SS effector delivery and enhances resistance by unknown mechanisms, and the addition of the bioactive metabolites similarly suppressed both aspects of PTI. Together, these results demonstrate that DC3000 perceives multiple signals derived from plants to initiate its T3SS and that the level of these host-derived signals impacts bacterial pathogenesis.