Abstract
The recent report of distinct Xanthomonas lineages of Xanthomonas arboricola pv. juglandis and Xanthomonas euroxanthea within the same walnut tree revealed that this consortium of walnut-associated Xanthomonas includes both pathogenic and nonpathogenic strains. As the implications of this co-colonization are still poorly understood, in order to unveil niche-specific adaptations, the genomes of three X. euroxanthea strains (CPBF 367, CPBF 424T, and CPBF 426) and of an X. arboricola pv. juglandis strain (CPBF 427) isolated from a single walnut tree in Loures (Portugal) were sequenced with two different technologies, Illumina and Nanopore, to provide consistent single scaffold chromosomal sequences. General genomic features showed that CPBF 427 has a genome similar to other X. arboricola pv. juglandis strains, regarding its size, number, and content of CDSs, while X. euroxanthea strains show a reduction regarding these features comparatively to X. arboricola pv. juglandis strains. Whole genome comparisons revealed remarkable genomic differences between X. arboricola pv. juglandis and X. euroxanthea strains, which translates into different pathogenicity and virulence features, namely regarding type 3 secretion system and its effectors and other secretory systems, chemotaxis-related proteins, and extracellular enzymes. Altogether, the distinct genomic repertoire of X. euroxanthea may be particularly useful to address pathogenicity emergence and evolution in walnut-associated Xanthomonas.
Highlights
Xanthomonas is a genus of gammaproteobacteria [1], which include numerous species acknowledged as important plant-associated bacteria with the capacity to cause disease in a wide range of plant species, including important agricultural crops [2,3]
When comparing the genome properties, while some features are similar between the four genomes, namely a G + C content around 65%, a number of coding genes proportional to genome size, and the number of rRNA operons and 5S tRNA genes, some other features are clearly distinct between the three X. euroxanthea strains (CPBF 367, CPBF 424T, and CPBF 426) and the
X. arboricola pv. juglandis strain CPBF 427. These differences are underlined by a higher genome size for the X. arboricola pv. juglandis strain CPBF 427 (5.23 Mb), in comparison with the slightly smaller genomes of X. euroxanthea strains CPBF 367, CPBF
Summary
Xanthomonas is a genus of gammaproteobacteria [1], which include numerous species acknowledged as important plant-associated bacteria with the capacity to cause disease in a wide range of plant species, including important agricultural crops [2,3]. The genus comprises 32 species (with validly published and correct names) [4], some of which are subdivided into distinct pathogenicity groups, known as pathovars, according to their high degree of host specificity, disease symptoms, and infection. Microorganisms 2021, 9, 624 mechanisms [5,6,7,8] Within this genus, Xanthomonas arboricola [9] is responsible for severe diseases in important stone fruits and nut trees [10]. It has been suggested that these genetic determinants of pathogenicity and virulence are under the control of tight transcriptional and post-transcriptional regulatory mechanisms that allow infective bacteria to adhere, invade the plant host tissues, and to multiply and overcome the plant defense mechanisms [21]
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