The helicase domain of the TMV replicase proteins induces the N-mediated defence response in tobacco

Authors

  • F. Les Erickson,

    1. Plant Gene Expression Center, University of California, Berkeley and United States Department of Agriculture, Agriculture Research Service, Albany, California 94710, USA,
    2. Department of Plant and Microbial Biology, University of California, Berkeley, California 94720, USA
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  • Steve Holzberg,

    1. Department of Environmental Science, Policy, and Management, University of California, Berkeley, California 94720, USA, and
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  • Alejandro Calderon-Urrea,

    1. Plant Gene Expression Center, University of California, Berkeley and United States Department of Agriculture, Agriculture Research Service, Albany, California 94710, USA,
    2. Department of Plant and Microbial Biology, University of California, Berkeley, California 94720, USA
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    • Present address: Department of Biology, California State University, Fresno, California 93740, USA.

  • Vanessa Handley,

    1. Plant Gene Expression Center, University of California, Berkeley and United States Department of Agriculture, Agriculture Research Service, Albany, California 94710, USA,
    2. Department of Plant and Microbial Biology, University of California, Berkeley, California 94720, USA
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  • Michael Axtell,

    1. Department of Plant and Microbial Biology, University of California, Berkeley, California 94720, USA
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  • Catherine Corr,

    1. Plant Gene Expression Center, University of California, Berkeley and United States Department of Agriculture, Agriculture Research Service, Albany, California 94710, USA,
    2. Department of Plant and Microbial Biology, University of California, Berkeley, California 94720, USA
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  • Barbara Baker

    1. Plant Gene Expression Center, University of California, Berkeley and United States Department of Agriculture, Agriculture Research Service, Albany, California 94710, USA,
    2. Department of Plant and Microbial Biology, University of California, Berkeley, California 94720, USA
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*For correspondence (fax +510 559 5678;
e-mail bbaker@socrates.berkeley.edu).

Summary

Tobacco mosaic virus (TMV) induces the hypersensitive response (HR) in tobacco plants containing the N gene. This defence response is characterized by cell death at the site of virus infection and inhibition of viral replication and movement. A previous study indicated that a portion of the TMV replicase containing a putative helicase domain is involved in HR induction. Here, this observation is confirmed and extended by showing that non-viral expression of a 50 kDa TMV helicase fragment (p50) is sufficient to induce the N-mediated HR in tobacco. Like the HR elicited by TMV infection, transgenic expression of p50 induces a temperature-sensitive defence response. We demonstrate that recombinant p50 protein has ATPase activity, as suggested by the presence of conserved sequence motifs found in ATPase/helicase enzymes. A point mutation that alters one of these motifs abolishes ATPase activity in vitro but does not affect HR induction. These results suggest that features of the TMV helicase domain, independent of its enzymatic activity, are recognized by N-containing tobacco to induce TMV resistance.

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