Regulation of Long-Chain N -Acyl-Homoserine Lactones in Agrobacterium vitis

Abstract

Homologs of quorum-sensing luxR and luxI regulatory genes, avsR and avsI, were identified in Agrobacterium vitis strain F2/5. Compared to other LuxI proteins from related species, the deduced AvsI shows the greatest identity to SinI (71%) from Sinorhizobium meliloti Rm1021. AvsR possesses characteristic autoinducer binding and helix-turn-helix DNA binding domains and shares a high level of identity with SinR (38%) from Rm1021. Site-directed mutagenesis of avsR and avsI was performed, and both genes are essential for hypersensitive-like response (HR) and necrosis. Two hypothetical proteins (ORF1 and ORF2) that are positioned downstream of avsR-avsI are also essential for the phenotypes. Profiles of N-acyl-homoserine lactones (AHLs) isolated from the wild type and mutants revealed that disruption of avsI, ORF1, or ORF2 abolished the production of long-chain AHLs. Disruption of avsR reduces long-chain AHLs. Expression of a cloned avsI gene in A. tumefaciens strain NT1 resulted in synthesis of long-chain AHLs. The necrosis and HR phenotypes of the avsI and avsR mutants were fully complemented with cloned avsI. The addition of synthetic AHLs (C 16:1 and 3-O-C 16:1 ) complemented grape necrosis in the avsR, avsI, ORF1, and ORF2 mutants. It was determined by reverse transcriptase PCR that the expression level of avsI is regulated by avsR but not by aviR or avhR, two other luxR homologs which were previously shown to be associated with induction of a tobacco hypersensitive response and grape necrosis. We further verified that avsR regulates avsI by measuring the expression of an avsI::lacZ fusion construct.

Bioluminescence in Vibrio fischeri is controlled by the redox‐responsive regulator ArcA

“…Second, 3-oxo-C6-HSL is diffusible and transmitted between cells (Kaplan and Greenberg, 1985). Both this feedforward signal amplification and diffusibility are features common among other autoinducers (Seed et al, 1995;Hao and Burr, 2006). Moreover, it is becoming increasingly clear that autoinducer synthases are regulated in response to specific environmental cues (Kim et al, 2005;Schuster and Greenberg, 2006;Dunn and Stabb, 2007), much as luxI is regulated by ArcAB.…”

LuxR-family ‘solos’: bachelor sensors/regulators of signalling molecules

“…A. vitis strain F2/5 most likely possesses two complete QS systems: the AvsI/R system responsible for the production of long-chain AHLs and another system that directs the production of short-chain AHLs (Hao & Burr, 2006). Both AviR and AvhR solos are required for induction of necrosis in grapes and hypersensitive response on non-host tobacco plants.…”

The quorum-sensing system AvsR-AvsI regulates both long-chain and short-chain acyl-homoserine lactones in Agrobacterium vitis E26

“…The amino acid sequence deduced from avsR E26 shows the highest similarity to AvsR F2/5 from A. vitis F2/5, with 92% identity, which is involved in the regulation of long-chain AHLs and the induction of hypersensitive response on tobacco and grape necrosis (Hao and Burr 2006).…”

“…In Agrobacterium tumefaciens, a traR/traI QS system is employed to regulate conjugal transfer of the pathogenic Ti plasmids (Li and Farrand 2000;Piper et al 1993;Zhang et al 1993). QS systems in A. vitis F2/5, a biocontrol agent against grapevine crown gall caused by strains of pathogenic A. vitis, are associated with induction of hypersensitive response on tobacco and necrosis on grape plants (Zheng et al 2003;Hao et al 2005;Hao and Burr 2006).…”