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Published online on August 15, 2007, 10.1073/pnas.0703203104 OPEN ACCESS ARTICLE


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Plant Biology
An inhibitor of viral RNA replication is encoded by a plant resistance gene

( Tm-1 | Tomato mosaic virus | inhibitory interaction )

Kazuhiro Ishibashi *{dagger}, Kiyoshi Masuda {dagger}, Satoshi Naito {ddagger}, Tetsuo Meshi *{sect}, and Masayuki Ishikawa *{sect}

*Division of Plant Sciences, National Institute of Agrobiological Sciences, Tsukuba 305-8602, Japan; {dagger}Graduate School of Agriculture and {ddagger}Graduate School of Life Science, Hokkaido University, Sapporo 060-8589, Japan; and {sect}CREST, Japan Science and Technology Agency, Kawaguchi 322-0012, Japan

Edited by David Baulcombe, The Sainsbury Laboratory, Norwich, United Kingdom, and approved July 3, 2007 (received for review April 6, 2007)

The tomato Tm-1 gene confers resistance to tomato mosaic virus (ToMV). Here, we report that the extracts of Tm-1 tomato cells (GCR237) have properties that inhibit the in vitro RNA replication of WT ToMV more strongly than that of the Tm-1-resistance-breaking mutant of ToMV, LT1. We purified this inhibitory activity and identified a polypeptide of {approx}80 kDa (p80GCR237) using LC–tandem MS. The amino acid sequence of p80GCR237 had no similarity to any characterized proteins. The p80GCR237 gene cosegregated with Tm-1; transgenic expression of p80GCR237 conferred resistance to ToMV within tomato plants; and the knockdown of p80GCR237 sensitized Tm-1 tomato plants to ToMV, indicating that Tm-1 encodes p80GCR237 itself. We further show that in vitro-synthesized Tm-1 (p80GCR237) protein binds to the replication proteins of WT ToMV and inhibits their function at a step before, but not after, the viral replication complex is formed on the membrane surfaces. Such binding was not observed for the replication proteins of LT1. These results suggest that Tm-1 (p80GCR237) inhibits the replication of WT ToMV RNA through binding to the replication proteins.

Author contributions: K.I. and M.I. designed research; K.I. performed research; K.M. contributed new reagents/analytic tools; K.I., S.N., T.M., and M.I. analyzed data; and K.I. and M.I. wrote the paper.

The authors declare no conflict of interest.

Freely available online through the PNAS open access option.

To whom correspondence should be addressed.

Masayuki Ishikawa, E-mail: ishika32{at}affrc.go.jp

www.pnas.org/cgi/doi/10.1073/pnas.0703203104
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