Young-Su Seo *, Maria R. Rojas *, Jung-Youn Lee
, Sang-Won Lee *, Jong-Seong Jeon *, Pamela Ronald *, William J. Lucas
, and Robert L. Gilbertson *¶
*Department of Plant Pathology and Section of Plant Biology, University of California,
Davis, CA 95616
Communicated by George Bruening, University of California, Davis,
CA, June 19, 2006 (received for review March 1, 2006)
Genes involved in a viral resistance response in common bean
(Phaseolus vulgaris cv. Othello) were identified by
inoculating a geminivirus reporter (Bean dwarf mosaic virus
expressing the green fluorescent protein), extracting RNA from tissue
undergoing the defense response, and amplifying sequences with
degenerate R gene primers. One such gene (a TIR-NBS-LRR gene,
RT4-4) was selected for functional analysis in which
transgenic Nicotiana benthamiana were generated and screened
for resistance to a range of viruses. This analysis revealed that
RT4-4 did not confer resistance to the reporter geminivirus;
however, it did activate a resistance-related response (systemic
necrosis) to seven strains of Cucumber mosaic virus (CMV) from
pepper or tomato, but not to a CMV strain from common bean. Of these
eight CMV strains, only the strain from common bean systemically
infected common bean cv. Othello. Additional evidence that
RT4-4 is a CMV R gene came from the detection of resistance
response markers in CMV-challenged leaves of RT4-4 transgenic plants,
and the identification of the CMV 2a gene product as the elicitor of
the necrosis response. These findings indicate that RT4-4 functions
across two plant families and is up-regulated in a non-virus-specific
manner. This experimental approach holds promise for providing
insights into the mechanisms by which plants activate resistance
responses against pathogens.
Author contributions: Y.-S.S., M.R.R., J.-Y.L., and R.L.G. designed research;
Y.-S.S. and S.-W.L. performed research; Y.-S.S., J.-Y.L., and J.-S.J.
contributed new reagents/analytic tools; Y.-S.S., M.R.R., P.R., W.J.L., and
R.L.G. analyzed data; and Y.-S.S., M.R.R., W.J.L., and R.L.G. wrote the
Conflict of interest statement: No conflicts declared.
Present address: Plant
and Soil Sciences, Delaware Biotechnology Institute, University of Delaware,
Newark, DE 19711.
Present address: Graduate
School of Biotechnology and Plant Metabolism Research Center, Kyung Hee
University, 1 Seochun, Gihung, Yongin, Kyungi 449-701, Republic of Korea.
¶To whom correspondence should be addressed.