Abstract
BackgroundXanthomonads are plant-associated bacteria responsible for diseases on economically important crops. Xanthomonas fuscans subsp. fuscans (Xff) is one of the causal agents of common bacterial blight of bean. In this study, the complete genome sequence of strain Xff 4834-R was determined and compared to other Xanthomonas genome sequences.ResultsComparative genomics analyses revealed core characteristics shared between Xff 4834-R and other xanthomonads including chemotaxis elements, two-component systems, TonB-dependent transporters, secretion systems (from T1SS to T6SS) and multiple effectors. For instance a repertoire of 29 Type 3 Effectors (T3Es) with two Transcription Activator-Like Effectors was predicted. Mobile elements were associated with major modifications in the genome structure and gene content in comparison to other Xanthomonas genomes. Notably, a deletion of 33 kbp affects flagellum biosynthesis in Xff 4834-R. The presence of a complete flagellar cluster was assessed in a collection of more than 300 strains representing different species and pathovars of Xanthomonas. Five percent of the tested strains presented a deletion in the flagellar cluster and were non-motile. Moreover, half of the Xff strains isolated from the same epidemic than 4834-R was non-motile and this ratio was conserved in the strains colonizing the next bean seed generations.ConclusionsThis work describes the first genome of a Xanthomonas strain pathogenic on bean and reports the existence of non-motile xanthomonads belonging to different species and pathovars. Isolation of such Xff variants from a natural epidemic may suggest that flagellar motility is not a key function for in planta fitness.
Highlights
Xanthomonads are plant-associated bacteria responsible for diseases on economically important crops
Genomic comparisons and Xanthomonas fuscans subsp. fuscans (Xff) 4834-R genome annotation enlighten features involved in plant pathogenicity and adaptation to different ecological niches
We identified 29 Type 3 Effectors (T3Es), including TALEs, depolymerizing carbohydrate enzymes, sensors of Two-Component Regulatory System (TCRS) and chemotaxis, TonB-dependent transporters (TBDT) and many proteins of unknown functions that could be involved in bean adaptation, colonization of xylem and other niches, the role of which remains to be explored
Summary
Xanthomonads are plant-associated bacteria responsible for diseases on economically important crops. The large host range of the genus strikingly contrasts with the typically narrow host range of individual strains that is restricted to one or several species of a botanical family [3]. Besides their very homogeneous phenotype, xanthomonads differ mainly by their host specificity. This is illustrated in the pathovar infrasubspecific division, which clusters bacterial strains causing similar symptoms on a same host range [4]
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