Plant & Animal Genome IX Conference

Poster: Large Insert Libraries, Gene Isolation, Etc.
P02_17.html

MOLECULAR ANALYSIS OF PARALOGS OF A RESISTANCE GENE CLUSTER IN TWO REPRESENTATIVE GENOTYPES OF THE MAJOR GENE POOLS OF Phaseolus vulgaris

¹ Laboratoire de Phytopathologie Moléculaire, Institut de Biotechnologie des Plantes, Bât 630, Université Paris-Sud, 91 405 Orsay, France.

² Dept. of Agronomy and Range Science, University of California, One Shields Ave., Davis, CA 95616-8515 USA

The interaction between Phaseolus vulgaris and the fungus Colletotrichum lindemuthianum constitutes a model system for the study of the molecular mechanisms underlying the evolution of resistance genes for three main reasons: i) existence of divergent and well-characterized gene pools, ii) occurrence of many specific resistance genes, and iii) evidence of co-evolution between the fungus and its host. A cluster of anthracnose resistance (R) genes, comprising both Andean and Mesoamerican specificities, was identified using a population from a cross between parents chosen to represent the two major P. vulgaris gene pools: BAT93 (Mesoamerican) and JaloEEP558 (Andean). The co-localization of Andean and Mesoamerican resistance specificities suggests that this locus existed prior to the separation of the two P. vulgaris gene pools. Four expressed genes (two from BAT93; two from JaloEEP558) were identified in the region containing this cluster of R-genes. These genes encode proteins containing nucleotide-binding site (NBS) and leucine-rich repeat (LRR) domains. A sequence comparison of these four R-like genes leads to two major observations. First, no features associating the R-like genes to either gene pool could be identified. However, the sequences could be organized into two subfamilies based on their genetic position in the R cluster. Second, Ka/Ks calculations revealed that the solvent-exposed residues of the C-terminal region of the LRR domain are subject to diversifying selection. In order to confirm these conclusions we are in the process of analyzing 15 additional sequences from either BAT93 or JaloEEP558 that are located at different genetic positions in the cluster.