Abstract
The aerobic plant pathogenic bacterium Xanthomonas campestris pv. vesicatoria (Xcv) colonizes the intercellular spaces of pepper and tomato. One enzyme that might contribute to the successful proliferation of Xcv in the host is the iron-sulfur protein aconitase, which catalyzes the conversion of citrate to isocitrate in the tricarboxylic acid (TCA) cycle and might also sense reactive oxygen species (ROS) and changes in cellular iron levels. Xcv contains three putative aconitases, two of which, acnA and acnB, are encoded by a single chromosomal locus. The focus of this study is aconitase B (AcnB). acnB is co-transcribed with two genes, XCV1925 and XCV1926, encoding putative nucleic acid-binding proteins. In vitro growth of acnB mutants was like wild type, whereas in planta growth and symptom formation in pepper plants were impaired. While acnA, XCV1925 or XCV1926 mutants showed a wild-type phenotype with respect to bacterial growth and in planta symptom formation, proliferation of the acnB mutant in susceptible pepper plants was significantly impaired. Furthermore, the deletion of acnB led to reduced HR induction in resistant pepper plants and an increased susceptibility to the superoxide-generating compound menadione. As AcnB complemented the growth deficiency of an Escherichia coli aconitase mutant, it is likely to be an active aconitase. We therefore propose that optimal growth and survival of Xcv in pepper plants depends on AcnB, which might be required for the utilization of citrate as carbon source and could also help protect the bacterium against oxidative stress.
Highlights
Pathogenic bacteria of the genus Xanthomonas infect both monoand dicotyledonous plants and they are responsible worldwide for considerable losses in plant productivity [1,2,3]
A similar gene organisation is observed in the plant pathogenic bacterium Xylella fastidiosa and in Stenotrophomonas maltophilia, both of which belong to the family Xanthomonadaceae
This gene order is not conserved in other gammaproteobacteria such as Escherichia coli (Fig. 1)
Summary
Pathogenic bacteria of the genus Xanthomonas infect both monoand dicotyledonous plants and they are responsible worldwide for considerable losses in plant productivity [1,2,3]. Vesicatoria (Xcv) causes bacterial spot disease on pepper and tomato plants and is a model bacterium for the study of bacterial pathogenesis [1]. It enters the plant through openings such as wounds or through stomata and colonizes the intercellular spaces between plant cells. To establish effective colonization of the host the bacterium has to acquire growth substrates successfully but presumably has to deal with a number of defense responses initiated by the host in response to infection. Iron-restriction and an induced oxidative stress response are likely to be important [6,7]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
