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Journal of Bacteriology, January 2005, p. 185-192, Vol. 187, No. 1
0021-9193/05/$08.00+0     doi:10.1128/JB.187.1.185-192.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

luxR Homolog avhR in Agrobacterium vitis Affects the Development of a Grape-Specific Necrosis and a Tobacco Hypersensitive Response

Guixia Hao,¹ Hongsheng Zhang,² Desen Zheng,¹ and Thomas J. Burr^1*

Department of Plant Pathology, New York State Agricultural Experiment Station, Cornell University, Geneva, New York,¹ Department of Agronomy, Nanjing Agricultural University, Nanjing, China²

Received 30 January 2004/ Accepted 16 September 2004

The luxR homolog aviR in Agrobacterium vitis strain F2/5 was recently shown to be associated with induction of a hypersensitive response (HR) on tobacco and necrosis on grape plants, indicating that the responses are regulated by quorum sensing. We now report a second luxR homolog, avhR, whose disruption (mutant M1320) results in HR-negative and reduced grape necrosis phenotypes. The deduced AvhR protein has characteristic autoinducer binding and DNA binding domains and is unique among reported functional LuxR homologs in having substitutions at highly conserved Asp70, Trp57, and Trp85 residues, which are predicted to play important roles in autoinducer binding in TraR. M1320 was fully complemented with cloned avhR. The same array of N-acylhomoserine lactones (AHL) from F2/5, M1320, and complemented M1320 were observed; however, the signal strength from extracts of 6-day-old M1320 cultures was stronger than that of F2/5. Cultures of F2/5 amended with AHL extracts from overnight and 6-day cultures of F2/5 and M1320 were not affected in ability to cause HR or necrosis. A region of about 14 kb flanking avhR was sequenced and compared with homologous regions of A. tumefaciens C58 and Sinorhizobium meliloti Rm1021 genomes. Gene order and homology are conserved between the species. A site-directed mutation in a putative gene that resides downstream of avhR and that has homology to genes belonging to the ATP-binding cassette transporter family did not affect HR or necrosis phenotypes. It was determined that avhR and aviR are expressed independently and that neither regulates the expression of a clpA homolog in F2/5.

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* Corresponding author. Mailing address: Department of Plant Pathology, NYSAES, Cornell University, Geneva, NY 14456. Phone: (315) 787-2312. Fax: (315) 787-2389. E-mail: tjb1{at}cornell.edu.

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Journal of Bacteriology, January 2005, p. 185-192, Vol. 187, No. 1
0021-9193/05/$08.00+0     doi:10.1128/JB.187.1.185-192.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

This article has been cited by other articles:

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