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Title: Genetic control of quorum-sensing signal turnover in Agrobacterium tumefaciens
Authors: Zhang, H.-B.
Wang, L.-H. 
Zhang, L.-H. 
Issue Date: 2-Apr-2002
Citation: Zhang, H.-B., Wang, L.-H., Zhang, L.-H. (2002-04-02). Genetic control of quorum-sensing signal turnover in Agrobacterium tumefaciens. Proceedings of the National Academy of Sciences of the United States of America 99 (7) : 4638-4643. ScholarBank@NUS Repository.
Abstract: A signal turnover system is an essential component of many genetic regulatory mechanisms. The best-known example is the ubiquitin-dependent protein degradation system that exists in many organisms. We found that Agrobacterium tumefaciens adopts a unique signal turnover system to control exiting from a quorum-sensing mode. A. tumefaciens regulates Ti plasmid conjugal transfer by a quorum-sensing signal, N-3-oxo-octanoyl homoserine lactone (3OC8HSL), also known as Agrobacterium autoinducer. By using Tn5 mutagenesis and a functional cloning approach, we identified two genes that are involved in switching from a conjugal quorum-sensing mode to a nonconjugal mode at the onset of stationary phase. First, we located attJ, which codes for an IcIR-type suppressor that regulates the second gene attM. The latter encodes a homologue of N-acylhomoserine lactone (AHL)-lactonase. Mass spectrometry analysis shows that the enzyme encoded by attM is an AHL-lactonase that hydrolyzes the lactone ring of 3OC8HSL. In wild-type A. tumefaciens, attM expression is initially suppressed by AttJ but significantly elevated at the stationary phase accompanied a sharp decline in 3OC8HSL. DNA gel retardation analysis shows that AttJ specifically binds to the promoter that controls AHL-lactonase expression. Mutation of attJ resulted in constitutive production of AHL-lactonase that abolishes 3OC8HSL accumulation and Ti plasmid transfer. These data suggest that A. tumefaciens has a sophisticated multicomponent quorum-sensing signal turnover system, allowing the cell to sense a change in growth and adjust cellular activities accordingly.
Source Title: Proceedings of the National Academy of Sciences of the United States of America
ISSN: 00278424
DOI: 10.1073/pnas.022056699
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