Submitted to: Walnut Research Conference
Publication Type: Proceedings
Publication Acceptance Date: January 1, 2008
Publication Date: January 1, 2008
Citation: Mcclean, A.E., Kluepfel, D.A. 2008. Biology of Brenneria Rubrifaciens: Screening for genes involved in pathogenesis . Walnut Research Conference. Technical Abstract: Deep bark canker of walnut trees is caused by the bacterium, Brenneria rubrifaciens. The disease is characterized by a chronic and debilitating decrease in yield and tree vigor. Symptoms of deep bark canker more often appear in trees at least 10 years old. The symptoms include the development of deep longitudinal cracks in trunks, scaffolds, and larger branches which exude a dark colored mixture of bacteria laden sap. Previous research suggests that B. rubrifaciens may reside in the vascular tissue of trees where it can lay dormant until a change in environmental conditions, such as water stress occurs resulting in the emergence of virulent bacteria and development of disease. A collection of B. rubrifaciens transposon mutants, was subjected to two biological screens in a bid to identify genes required for pathogenicity. Eighty-four mutants were screened in a tobacco leaf bioassay to evaluate hypersensitive response (HR) elicitation. Only 3 of the 84 mutants failed to elicit a HR in tobacco leaves. Genetic analysis revealed these three mutants had insertions in two genetic loci, open reading frames (ORFs) encoding an autoinducer synthetase homolog (mutants Br-212 and Br-512) and rpoN-like '54 factor for RNA II polymerase (mutant Br-415). Twelve mutants were screened for a response on tissue cultured Hartley walnut plants. Two of the twelve mutants tested were reduced in their ablility to cause necrosis on tissue cultured walnut plants (mutants Br-212 and Br-415). These findings indicate that two mechanisms: '54 dependent transcription and quorum sensing, a method of communication among bacterial cells, are involved in conferring pathogenesis on walnuts plants and a HR in tobacco.