Abstract
In Agrobacterium tumefaciens, horizontal transfer and vegetative replication of oncogenic Ti plasmids involve a cell-to-cell communication process called quorum-sensing (QS). The determinants of the QS-system belong to the LuxR/LuxI class. The LuxI-like protein TraI synthesizes N-acyl-homoserine lactone molecules which act as diffusible QS-signals. Beyond a threshold concentration, these molecules bind and activate the LuxR-like transcriptional regulator TraR, thereby initiating the QS-regulatory pathway. For the last 20 years, A. tumefaciens has stood as a prominent model in the understanding of the LuxR/LuxI type of QS systems. A number of studies also unveiled features which are unique to A. tumefaciens QS, some of them being directly related to the phytopathogenic lifestyle of the bacteria. In this review, we will present the current knowledge of QS in A. tumefaciens at both the genetic and molecular levels. We will also describe how interactions with plant host modulate the QS pathway of A. tumefaciens, and discuss what could be the advantages for the agrobacteria to use such a tightly regulated QS-system to disseminate the Ti plasmids.
Highlights
In its canonical definition, quorum-sensing (QS) refers to a process through which a bacterial population is able to monitor its cell density and to mount coordinate responses (Fuqua et al, 1994)
OC8HSL-ASSOCIATED PLANT RESPONSES The interactions between A. tumefaciens and plant hosts are mediated by several factors, from the phenolic compounds accumulated at wound sites that induce the expression of the Ti plasmid vir genes, to the opines produced in the tumor niche that control horizontal transfer of bacterial plasmids
In this review, we described the A. tumefaciens TraI/TraR QS system and showed how it exquisitely regulated the dissemination of Ti plasmids
Summary
Institut des Sciences du Végétal, UPR2355, Centre National de la Recherche Scientifique, Gif-sur-Yvette, France. Reviewed by: Clay Fuqua, Indiana University, USA Franz Narberhaus, Ruhr University Bochum, Germany. The determinants of the QS-system belong to the LuxR/LuxI class. The LuxI-like protein TraI synthesizes N-acyl-homoserine lactone molecules which act as diffusible QS-signals. These molecules bind and activate the LuxR-like transcriptional regulator TraR, thereby initiating the QS-regulatory pathway. For the last 20 years, A. tumefaciens has stood as a prominent model in the understanding of the LuxR/LuxI type of QS systems. We will present the current knowledge of QS in A. tumefaciens at both the genetic and molecular levels. We will describe how interactions with plant host modulate the QS pathway of A. tumefaciens, and discuss what could be the advantages for the agrobacteria to use such a tightly regulated QS-system to disseminate the Ti plasmids
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