Plant & Animal Genome IX Conference

Poster: Large Insert Libraries, Gene Isolation, Etc.
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Physical map of the Citrus tristeza virus resistance (Ctv) gene locus

¹ Dept. of Plant Pathology and Microbiology, The Texas A&M University Agricultural Experiment Station, Weslaco, TX 78596

² Department of Botany and Plant Sciences, University of California at Riverside, Riverside, CA 92521

The Citrus tristeza virus resistance gene (Ctv) is a single dominant gene in Poncirus trifoliata, a sexually compatible relative of citrus. In order to clone this gene, a bacterial artificial chromosome (BAC) library has been constructed from an individual plant that was homozygous for Ctv. This library contains 45,696 clones with an average insert size of 80 kb, corresponding to 9.6 genome equivalents. Screening of the BAC library with five chloroplast DNA probes indicated that 0.58% of the BAC clones contained chloroplast derived inserts. The chromosome walk across the Ctv locus was initiated using three closely linked genetic markers: C19, AD8 and Z16. The walk has been completed and a contig of ca. 1.2 Mb was constructed. Based on new data, the genetic map in the Ctv region was revised with Ctv located between AD8/Z16 and C19 at distances of 1.2 and 0.6 cM, respectively. Utilizing DNA fragments isolated from the contig as RFLP markers, the Ctv locus was further delimited to a region of ca. 300 kb. This contig contains several putative disease resistance genes similar to the rice Xa21 gene, the tomato Cf-2 gene, and the Arabidopsis thaliana RPS2 gene. Further progress towards identification of Ctv will be presented.