Linear Plasmids and Phytopathogenicity

Isolde Francis1'2 • Dirk Gevers1'3 • Mansour Karimi1'2 • Marcelle Holsters1'2'4 (K) • Danny Vereecke1'2

1 Department of Plant Systems Biology VIB; Technologiepark 927; 9052 Ghent' Belgium 2Department of Molecular Genetics' Ghent University 9052 Ghent' Belgium

3 Laboratory of Microbiology Ghent University K.L. Ledeganckstraat 35' 9000 Ghent' Belgium [email protected] 4To whom correspondence should be addressed: Department of Plant Systems Biology

VIB, Universiteit Ghent, Technologiepark 927, 9052 Ghent, Belgium

1 Introduction 100

2 Rhodococcus, a Metabolically Diverse Genus of the Actinomycetes 101

3 The Linear Plasmid pFiD188 of R. fascians Strain D188

is Closely Related to Linear Plasmids of Other Rhodococcus Strains 103

4 Virulence Determinants on the Linear Plasmid pFiD188 105

5 Cross Talk Between the Linear Plasmid pFiD188 and the Chromosome . . 108

6 An Overview of the Infection Process: Putting the Players in Place 109 References 111

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 pFiD 188 are involved in specific aspects of the interaction.

Abbreviations att Attenuated fas Fasciation

HGT Horizontal gene transfer hyp Hypervirulent iaa Indole-3-acetic acid nrp Nonribosomal peptide

NRPS Nonribosomal peptide synthetase

ORF Open reading frame

PAI Pathogenicity island stk Serine threonine kinase

TIR Terminal inverted repeat vic Virulence on the chromosome

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