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PLANTS INTERACTING WITH OTHER ORGANISMS

Tomato Transcriptional Changes in Response to Clavibacter michiganensis subsp. michiganensis Reveal a Role for Ethylene in Disease Development^1,[W]

Department of Plant Sciences, Tel Aviv University, Tel Aviv 69978, Israel (V.B., M.M., O.S., I.B., G.S.); Department of Pediatric Hemato-Oncology, Safra Children's Hospital and Cancer Research Center, Sheba Medical Center, Tel Hashomer 52621, Israel (J.J.-H., G.R.); Department of Genetechnology/Microbiology, University of Bielefeld, D–33615 Bielefeld, Germany (R.E.); United Nations Educational, Scientific and Cultural Organization Biotechnology Center, Bethlehem University, Bethlehem, Palestinian Authority (N.I.); Department of Plant Pathology and Weed Research, Agricultural Research Organization, Volcani Center, Bet Dagan 50250, Israel (S.M.-S.)

Clavibacter michiganensis subsp. michiganensis (Cmm) is a gram-positive actinomycete, causing bacterial wilt and canker disease in tomato (Solanum lycopersicum). Host responses to gram-positive bacteria and molecular mechanisms associated with the development of disease symptoms caused by Cmm in tomato are largely unexplored. To investigate plant responses activated during this compatible interaction, we used microarray analysis to monitor changes in host gene expression during disease development. This analysis was performed at 4 d postinoculation, when bacteria were actively multiplying and no wilt symptoms were yet visible; and at 8 d postinoculation, when bacterial growth approached saturation and typical wilt symptoms were observed. Of the 9,254 tomato genes represented on the array, 122 were differentially expressed in Cmm-infected plants, compared with mock-inoculated plants. Functional classification of Cmm-responsive genes revealed that Cmm activated typical basal defense responses in the host, including induction of defense-related genes, production and scavenging of free oxygen radicals, enhanced protein turnover, and hormone synthesis. Cmm infection also induced a subset of host genes involved in ethylene biosynthesis and response. After inoculation with Cmm, Never ripe (Nr) mutant plants, impaired in ethylene perception, and transgenic plants with reduced ethylene synthesis showed significant delay in the appearance of wilt symptoms, compared with wild-type plants. The retarded wilting in Nr plants was a specific effect of ethylene insensitivity, and was not due to altered expression of defense-related genes, reduced bacterial populations, or decreased ethylene synthesis. Taken together, our results indicate that host-derived ethylene plays an important role in regulation of the tomato susceptible response to Cmm.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Guido Sessa (guidos{at}post.tau.ac.il).

^[W] The online version of this article contains Web-only data.

www.plantphysiol.org/cgi/doi/10.1104/pp.107.115188

^* Corresponding author; e-mail guidos{at}post.tau.ac.il.

Received December 23, 2007; accepted January 24, 2008; published February 1, 2008.