PAG-IV Plant Genome IV Conference

Town & Country Conference Center, San Diego, CA, January, 1995.

P4
Structure of the Pto/Prf Resistance Locus in Tomato

DANIEL LAVELLE(1), Giles Oldroyd(2), Doug Dahlbeck(2), Jeff Chang(1), John Salmeron(3), Steve Scofield(1), Brian Staskawicz(1,2) and RICHARD MICHELMORE(1,4)
1. NSF Center for Engineering Plants for Resistance Against Pathogens, University of California, Davis, CA 95616, USA
2. Dept. of Plant Biology, University of California, Berkeley, CA, USA
3. CIBA-Geigy, Research Triangle, NC, USA
4. Dept. of Vegetable Crops, University of California, Davis, CA 95616, USA

Disease resistance genes are often clustered in the genome. We are sequencing the Pto/Prf locus of tomato cv. Rio Grande 76R which is a line of L. esculentum with the Pto/Prf locus introgressed from L. pimpinellifolium. Mutational analysis has identified two genes, Pto and Prf, that are required for resistance to strains of Pseudomonas syringae pv tomato expressing avrPto. The product of Pto is a serine/threonine kinase; the inferred product of Prf contains a leucine rich repeat (LRR) and P-loop domain. Prf as well as at least four Pto homologs reside within a 50 Kb region in 76R. One Pto homolog, Fen, confers sensitivity to fenthion, the active agent in some obsolete insecticides. The Pto homologs share great sequence similarity; therefore, they may constitute a family of duplicated genes which have evolved to possess different specificities. A contig of cosmids was made from a Yeast Artificial Chromosome clone containing the Pto/Prf locus. The cosmids were ordered using restriction fragment analysis and AFLP fingerprinting. Random and ordered subclones were generated from the cosmids and are currently being sequenced on a Licor 4000L automated DNA sequencer. We have so far sequenced over 35 Kb of the region. Preliminary sequence analysis identified an additional expressed member of the Pto gene family. We are studying the sequence divergence and similarity of the homologs. We are comparing the sequence of the region to itself using DNA matrix algorithms to look for patterns of duplication. Preliminary analysis indicates that there is little duplication outside of the open reading frames for the Pto homologs. We are also interested in the transcriptional complexity of this disease resistance locus. We have so far found only two other long open reading frames. One has similarity to a retrotransposon; the other has no significant similarity to protein sequences in the database.

Return to Previous Page or Intl-PAG Homepage