October
2014
, Volume
27
, Number
10
Pages
1,035
-
1,047
Authors
Alon Savidor,1,2
Laura Chalupowicz,3
Doron Teper,1
Karl-Heinz Gartemann,1,4
Rudolf Eichenlaub,4
Shulamit Manulis-Sasson,3
Isaac Barash,1 and
Guido Sessa1
Affiliations
1Department of Molecular Biology and Ecology of Plants, Tel Aviv University, Tel Aviv 69978, Israel; 2The Nancy & Stephen Grand Israel National Center for Personalized Medicine, Weizmann Institute of Science, Rehovot 7610001, Israel; 3Department of Plant Pathology and Weed Research, ARO, the Volcani Center, Bet Dagan 50250, Israel; 4Department of Genetechnology/Microbiology, Faculty of Biology, University of Bielefeld, 33501 Bielefeld, Germany
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Accepted 9 June 2014.
Abstract
The plant pathogen Clavibacter michiganensis subsp. michiganensis is a gram-positive bacterium responsible for wilt and canker disease of tomato. Although disease development is well characterized and diagnosed, molecular mechanisms of C. michiganensis subsp. michiganensis virulence are poorly understood. Here, we identified and characterized two C. michiganensis subsp. michiganensis transcriptional regulators, Vatr1 and Vatr2, that are involved in pathogenicity of C. michiganensis subsp. michiganensis. Vatr1 and Vatr2 belong to TetR and MocR families of transcriptional regulators, respectively. Mutations in their corresponding genes caused attenuated virulence, with the Δvatr2 mutant showing a more dramatic effect than Δvatr1. Although both mutants grew well in vitro and reached a high titer in planta, they caused reduced wilting and canker development in infected plants compared with the wild-type bacterium. They also led to a reduced expression of the ethylene-synthesizing tomato enzyme ACC-oxidase compared with wild-type C. michiganensis subsp. michiganensis and to reduced ethylene production in the plant. Transcriptomic analysis of wild-type C. michiganensis subsp. michiganensis and the two mutants under infection-mimicking conditions revealed that Vatr1 and Vatr2 regulate expression of virulence factors, membrane and secreted proteins, and signal-transducing proteins. A 70% overlap between the sets of genes positively regulated by Vatr1 and Vatr2 suggests that these transcriptional regulators are on the same molecular pathway responsible for C. michiganensis subsp. michiganensis virulence.
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