Abstract
The genus Agrobacterium contains a group of plant-pathogenic bacteria that have been developed into an important tool for genetic transformation of eukaryotes. To further improve this biotechnology application, a better understanding of the natural genetic variation is critical. During the process of isolation and characterization of wild-type strains, we found a novel strain (i.e., NCHU2750) that resembles Agrobacterium phenotypically but exhibits high sequence divergence in several marker genes. For more comprehensive characterization of this strain, we determined its complete genome sequence for comparative analysis and performed pathogenicity assays on plants. The results demonstrated that this strain is closely related to Neorhizobium in chromosomal organization, gene content, and molecular phylogeny. However, unlike the characterized species within Neorhizobium, which all form root nodules with legume hosts and are potentially nitrogen-fixing mutualists, NCHU2750 is a gall-forming pathogen capable of infecting plant hosts across multiple families. Intriguingly, this pathogenicity phenotype could be attributed to the presence of an Agrobacterium-type tumor-inducing plasmid in the genome of NCHU2750. These findings suggest that these different lineages within the family Rhizobiaceae are capable of transitioning between ecological niches by having novel combinations of replicons. In summary, this work expanded the genomic resources available within Rhizobiaceae and provided a strong foundation for future studies of this novel lineage. With an infectivity profile that is different from several representative Agrobacterium strains, this strain may be useful for comparative analysis to better investigate the genetic determinants of host range among these bacteria.
Highlights
Agrobacterium tumefaciens is a soil-dwelling bacterium often associated with plants (Nester 2015)
The genus Agrobacterium contains a group of plant-pathogenic bacteria that have been developed into an important tool for genetic transformation of eukaryotes
With an infectivity profile that is different from several representative Agrobacterium strains, this strain may be useful for comparative analysis to better investigate the genetic determinants of host range among these bacteria
Summary
Agrobacterium tumefaciens is a soil-dwelling bacterium often associated with plants (Nester 2015). One important feature of the Agrobacterium-mediated DNA transfer is that none of the genes encoded on the TDNA is required for transformation. This allows for the replacement of wild-type T-DNA with other genes of interest. One limitation is that many plant species and cultivars have remained difficult to be transformed by the commonly used strains of A. tumefaciens To overcome this limitation, overexpression of the virulence (vir) genes or other modifications have been shown to be effective in some cases (Hellens et al 2000; Gelvin 2003; Banta and Montenegro 2008; Hiei et al 2014; Wu et al 2014; Hwang et al 2015). To better understand this strain, we determined its complete genome sequence and conducted comparative analysis
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