Gene shuffling-generated and natural variants of the tomato resistance gene Cf-9 exhibit different auto-necrosis-inducing activities in Nicotiana species

Authors

  • Brande B.H. Wulff,

    1. The Sainsbury Laboratory, John Innes Centre, Norwich Research Park, Colney Lane, Norwich NR4 7UH, UK
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    • Present address: Instituto de Biología Molecular y Celular de Plantas, Universidad Politécnica de Valencia, Camino de Vera s/n, Valencia, Spain.

    • §The contribution of these authors should be considered equal.

  • Marco Kruijt,

    1. Laboratory of Phytopathology, Wageningen University, Binnenhaven 5, 6709 PD, Wageningen, The Netherlands
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    • §The contribution of these authors should be considered equal.

  • Peter L. Collins,

    1. The Sainsbury Laboratory, John Innes Centre, Norwich Research Park, Colney Lane, Norwich NR4 7UH, UK
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  • Colwyn M. Thomas,

    1. School of Biological Sciences, University of East Anglia, Norwich, NR4 7TJ, UK
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  • Andrea A. Ludwig,

    1. The Sainsbury Laboratory, John Innes Centre, Norwich Research Park, Colney Lane, Norwich NR4 7UH, UK
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    • Present address: Centre of Molecular Plant Biology, Eberhard-Karls University Tübingen, Auf der Morgenstelle 5, 72076 Tübingen, Germany.

  • Pierre J.G.M. De Wit,

    1. Laboratory of Phytopathology, Wageningen University, Binnenhaven 5, 6709 PD, Wageningen, The Netherlands
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  • Jonathan D.G. Jones

    Corresponding author
    1. The Sainsbury Laboratory, John Innes Centre, Norwich Research Park, Colney Lane, Norwich NR4 7UH, UK
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(fax: +44 1603 450011; e-mail jonathan.jones@sainsbury-laboratory.ac.uk).

Summary

Tomato Cf genes encode membrane-bound proteins with extracellular leucine-rich repeats, and confer resistance to the fungal tomato pathogen Cladosporium fulvum, and a hypersensitive response (HR) to C. fulvum-derived race-specific elicitors. Several Cf genes, including Cf-4 and Cf-9, are members of the highly homologous Hcr9 (homologues of C. fulvumresistance gene Cf-9) gene family. Hcr9s evolve mainly by sequence exchange between paralogues, by which novel Cf genes may be generated. To mimic this aspect of natural evolution, we generated chimeras between multiple Hcr9s in vitro by gene shuffling. The shufflants were tested for novel specificities by transient expression in Nicotiana benthamiana. Many shufflants induced an HR in the absence of fungal elicitors and were designated auto-activators. We also identified two natural Hcr9 auto-activators in the wild tomato species Lycopersicon peruvianum, which induced an HR upon expression in N. benthamiana. The Hcr9 auto-activators exhibit different auto-necrosis-inducing specificities in five selected species of the Nicotiana genus, and they were shown to function in the same signalling pathway as Cf-9. Auto-activating alleles of nucleotide binding site–leucine-rich repeat genes and the protein kinase Pto were previously described. The auto-activators described here, belonging to the Cf-like structural class of resistance genes, shed light on this important phenotype and may be used as tools to unravel the mechanisms by which this class of resistance proteins function.

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