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Developmental Control of Promoter Activity Is Not Responsible for Mature Onset of Cf-9B-Mediated Resistance to Leaf Mold in Tomato

November 2002 , Volume 15 , Number  11
Pages  1,099 - 1,107

S. N. Panter , 1 K. E. Hammond-Kosack , 2 K. Harrison , 2 J. D. G. Jones , 2 and D. A. Jones 1

1Research School of Biological Sciences, Australian National University, Canberra ACT 0200 Australia; 2Sainsbury Laboratory, John Innes Centre, Colney Lane, Norwich NR4 7UH, Norfolk, U.K.

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Accepted 26 July 2002.

Cf-9 confers resistance to tomato seedlings and mature plants against Cladosporium fulvum races expressing the Avr9 elicitor. It is the central member of a cluster of five paralogous genes in an introgressed segment of chromosome 1 derived from Lycopersicon pimpinellifolium. The other four genes have been named Hcr9-9A, Hcr9-9B, Hcr9-9D, and Hcr9-9E. Hcr9-9B, here designated Cf-9B, encodes weaker resistance than Cf-9, recognizes a different elicitor, and protects only mature plants from infection. The onset of Cf-9B-mediated resistance and the molecular basis for its developmental control were investigated in this study. Fungal inoculation of tomato plants containing reciprocal Cf-9/Cf-9B promoter-coding region swaps, analysis of tomato plants containing promoter-gusA fusions, and a reverse transcriptase-polymerase chain reaction study of Cf-9 and Cf-9B transcripts in tomato plants suggested that transcriptional control of Cf-9B did not account for the late onset of Cf-9B-mediated resistance. Alternative explanations for the onset of Cf-9B-mediated resistance in mature plants are discussed.

Additional keywords: avirulence gene , guard hypothesis , Milky Way locus , resistance gene .

© 2002 The American Phytopathological Society