Raiders of the lost hrc: The search for the elusive Pantoea agglomerans Type III Secretion System
Type III Secretion Systems (T3SS) are complex extracellular nanomachines used by Gram-negative bacteria to inject virulence factors directly into their hosts. The T3SS, often referred to as a hrc cluster, is made up of 20 – 27 genes referred to as hypersensitivity response and conserved proteins (hrp/hrc). The T3SS is essential to the pathogenic abilities of these bacteria as it allows for the injection of virulence proteins, or Type III Secretion Effectors (T3SE) into eukaryotic cells. These T3SEs manipulate host defence mechanisms and signal transduction pathways to facilitate pathogenesis. The dual animal-plant pathogen P. agglomerans was recently identified to have both an animal T3SS and a plant T3SS, however initial attempts to determine the structural organization of the system indicated that its organization is unique and unrelated to that of its closest relatives Pantoea stewartii and Erwinia amylovora. Furthermore, only three T3SEs have been isolated and characterized in P. agglomerans. The purpose of this work is to sequence the T3SS in P. agglomerans in order to gain a better understanding of its function in pathogenesis and provide insight into the evolution of the T3SS across plant and animal pathogens. Additionally, a novel cloning vector is currently being constructed which will allow for a high throughput genetic screen to identify novel T3SEs in P. agglomerans. The identification of novel T3SEs and structural organization of the T3SS will provide a better understanding of both the mechanisms of plant pathogenic capabilities of P. agglomerans and the organization of the T3SS and its regulation.