The Cell-Cell Communication System of Agrobacterium Tumefaciens
The Ti plasmids of Agrobacterium tumefaciens carry almost all of the genes required for the formation of crown gall tumors and for the utilization of opines that are produced by these tumors. These plasmids also encode a cell-cell signalling (quorum sensing) system that is homologous to the LuxR-LuxI system of Vibrio fischeri. The LuxI orthologue TraI synthesizes a specific N-acylhomoserine lactone (AHL). This AHL is a diffusible signalling molecule and, when it accumulates to a sufficiently high concentration, it interacts with the LuxR-type transcription activator TraR. The traR gene is induced by particular opines, causing quorum sensing in this bacterium to occur only in the presence of these compounds. TraR activates genes required for conjugal transfer and vegetative replication of the Ti plasmid. In this chapter, we discuss the quorum sensing system of A. tumefaciens from a molecular perspective, and speculate on the possible roles this system may have in virulence and plant colonization.
KeywordsAgrobacterium Tumefaciens Quorum Sensing Conjugal Transfer Crown Gall Tumor Fatty Acid Tail
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