The leafy gall syndrome induced by Rhodococcus fascians

Authors

  • Elisabeth Stes,

    1. Department of Plant Biotechnology and Bioinformatics, Ghent University, Gent, Belgium
    Current affiliation:
    1. Department of Medical Protein Research, VIB and Department of Biochemistry, Ghent University, Gent, Belgium
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  • Isolde Francis,

    1. Department of Plant Biotechnology and Bioinformatics, Ghent University, Gent, Belgium
    Current affiliation:
    1. Department of Plant Pathology, University of Florida, Gainesville, FL, USA
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  • Ine Pertry,

    1. Department of Plant Biotechnology and Bioinformatics, Ghent University, Gent, Belgium
    Current affiliation:
    1. Institute of Plant Biotechnology Outreach, Ghent University, Gent, Belgium
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  • Alicja Dolzblasz,

    1. Institute of Experimental Biology, Department of Plant Developmental Biology, Wrocław University, Wrocław, Poland
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  • Stephen Depuydt,

    1. Department of Plant Biotechnology and Bioinformatics, Ghent University, Gent, Belgium
    2. Department of Plant Systems Biology, VIB, Gent, Belgium
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  • Danny Vereecke

    Corresponding author
    1. Department of Plant Production, University College Ghent, Ghent University, Gent, Belgium
    • Department of Plant Biotechnology and Bioinformatics, Ghent University, Gent, Belgium
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Correspondence: Danny Vereecke, Laboratory of Plant Biotechnology, Department of Plant Production, University College Ghent, Gebouw C – room C4.52, Valentin Vaerwyckweg 1, 9000 Gent, Belgium. Tel.: +32 9 248 88 59;

fax: +32 9 242 42 79;

e-mail: danny.vereecke@hogent.be

Abstract

The Actinomycete Rhodococcus fascians causes the leafy gall syndrome, an infectious plant disease that affects a wide range of plants, primarily dicotyledonous herbs. The syndrome is associated with delayed senescence, loss of apical dominance, activation of dormant axillary meristems, and formation of multiple inflorescences, leading to a stunted and bushy plant appearance. A major breakthrough in the elucidation of the virulence strategy of this pathogen was the discovery of a linear virulence plasmid, pFiD188 for R. fascians strain D188. Upon perception of a compatible host plant, an autoregulatory mechanism mediated by the att operon directs a switch in the bacterial life style from a harmless epiphyte into a pathogenic endophyte and, concomitantly, activates gene expression of the fas operon that encodes a cytokinin biosynthesis pathway. A mixture of five cytokinins determines the cytokinin activity of R. fascians that directly affects plant responses and development. Moreover, the bacterial cytokinins stimulate the host to produce auxins and polyamines, that function as accessory signals to aid in symptom development. The plant reacts against the developmental hijacking by R. fascians by activating a set of counteracting measures that ultimately results in a delicate balance, allowing a long-lasting biotrophic interaction.

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