Linear Plasmids and Phytopathogenicity

Abstract

The occurrence of plasmids is typically correlated with the acquisition of specialized traits that can be very diverse. Production of secondary metabolites, achievement of complex catabolic reactions, and adaptation to particular habitats are just a few examples of functions that are often encoded by circular or linear extrachromosomal replicons. Although virulence is another classical characteristic that is frequently associated with the presence of plasmids, until now there is only one known case in which the phytopathogenic capacity is encoded by a linear plasmid. The actinomycete Rhodococcus fascians is a wide-spectrum plant pathogen that provokes shooty neoplastic outgrowths on its hosts. The key virulence determinants of this bacterium are located on a linear replicon of the invertron type. Even though the sequence determination of the linear plasmid of R. fascians strain D188 (pFiD188) is not completed, a first comparative analysis shows that is has probably a common origin with catabolic linear plasmids of other Rhodococcus strains. Whereas the colinear regions encode plasmid maintenance functions, the three unique regions of pFiD188 are involved in specific aspects of the interaction.