Plant & Animal Genome IX Conference

Poster: Large Insert Libraries, Gene Isolation, Etc.
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MAP-BASED CLONING OF RESISTANCE GENE HOMOLOGUES IN THE VF-REGION OF THE APPLE (MALUS SP.)

¹ Swiss Federal Inst. of Technology Zuerich - Inst. of Plant Sciences - Plant Pathology group, Universitaetst. 2, Zuerich, CH-8092, Switzerland

² University of Bologna - Dipartimento di Colture Arboree, Via Filippo Re 6, Bologna, ,I-40126, Italy

A map-based cloning project was started to isolate Vf, a single dominant gene derived from Malus floribunda 821, that confers resistance against apple scab (V. inaequalis). Recent efforts have concentrated on the construction of a BAC contig spanning the genomic region between the molecular markers M18 and AM19 bracketing the Vf gene. The inserts of the five BAC clones of the contig that compose the minimum 'tiling path' spanning the Vf-region were used as probe to screen a cDNA library made from leaves of the apple variety 'Florina' (heterozygous for the Vf gene) inoculated with a conidial suspension of V. inaequalis. This allowed us to identifya cluster of receptor-like genes with high homology to members of the Cf resistance gene family of tomato. The predicted amino acid sequence contains an extra-cellular leucine-rich repeat domain and a putative trans-membrane domain. These genes have been named HcrVf (Homologues of Cladosporium fulvum resistance genes of the Vf-region). The gene cluster is present on the chromosome in coupling with resistance as well as on the other one in repulsion. The cluster in cis with the Vf gene is composed of a minimum of 5 to a maximum of 14 HcrVf genes. Three of the genes were sequenced completely. RT-PCR experiments have shown that two of them are constitutively expressed in leaves while the third one is not expressed.