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Phenotypic and Molecular-Phylogenetic Analyses Reveal Distinct Features of Crown Gall-Associated Xanthomonas Strains

Abstract : In summer 2019, widespread occurrence of crown gall disease caused by Agrobacterium spp. was observed on commercially grown ornamental plants in south- ern Iran. Beside agrobacteria, pale yellow-pigmented Gram-negative strains resembling the members of Xanthomonas were also associated with crown gall tissues on weep- ing fig (Ficus benjamina) and Amaranthus sp. plants. The purpose of the present study was to characterize the crown gall-associated Xanthomonas strains using plant inocula- tion assays, molecular-phylogenetic analyses, and comparative genomics approaches. Pathogenicity tests showed that the Xanthomonas strains did not induce disease symptoms on their host of isolation. However, the strains induced hypersensitive reac- tion on tobacco, geranium, melon, squash, and tomato leaves via leaf infiltration. Multilocus sequence analysis suggested that the strains belong to clade IA of Xanthomonas, phylogenetically close to Xanthomonas translucens, X. theicola, and X. hyacinthi. Average nucleotide identity and digital DNA-DNA hybridization values between the whole-genome sequences of the strains isolated in this study and refer- ence Xanthomonas strains are far below the accepted thresholds for the definition of prokaryotic species, signifying that these strains could be defined as two new species within clade IA of Xanthomonas. Comparative genomics showed that the strains iso- lated from crown gall tissues are genetically distinct from X. translucens, as almost all the type III secretion system genes and type III effectors are lacking in the former group. The data obtained in this study provide novel insight into the breadth of genetic diversity of crown gall-associated bacteria and pave the way for research on gall-associated Xanthomonas-plant interactions.
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Submitted on : Friday, June 10, 2022 - 8:52:41 AM
Last modification on : Thursday, September 22, 2022 - 4:25:59 PM
Long-term archiving on: : Sunday, September 11, 2022 - 6:14:53 PM

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Hamzeh Mafakheri, S. Mohsen Taghavi, Sadegh Zarei, Touraj Rahimi, Mohammad Sadegh Hasannezhad, et al.. Phenotypic and Molecular-Phylogenetic Analyses Reveal Distinct Features of Crown Gall-Associated Xanthomonas Strains. Microbiology Spectrum, American Society for Microbiology, 2022, 10 (1), 18 p. ⟨10.1128/spectrum.00577-21⟩. ⟨hal-03576592⟩

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