Molecular diversity at the <em>Vat/Pm-W</em> resistance locus in melon
2008
Dogimont, Catherine | Chovelon, Veronique | Tual, Sarah | Boissot, Nathalie | Rittener-Ruff, Vincent | Giovinazzo, Nathalie | Bendahmane, Abdelhafid,
The resistance Vat gene of melon was isolated by map-based cloning. It encodes a protein with a coiled coil domain (CC), a nucleotide binding site (NBS) and leucine–rich repeats (LRR). Whereas most resistance genes confer resistance to a single pathogen, two alleles with different resistance specificities were identified at the locus. The Vat allele confers resistance to plant colonization by the aphid Aphis gossypii and to transmission of unrelated viruses by this vector specifically; the Pm-W allele confers resistance to the powdery mildew Podosphaera xanthii. Here we identified Vat-analogs in several melon genotypes using Long Range PCR, cloning and sequencing of full-length fragments. Several sources of variability were identified: (i) a different number of analogs were identified, suggesting a variable complexity of the gene cluster depending on the genotype, (ii) the number of repeats of a conserved motif of 65 amino acids within the LRR domain varied from two to five; this variation may be involved in the specific recognition of aphids or powdery mildew, (iii) finally, while the Vat allele seems to be shared by several aphid resistant accessions from various geographical origins, other alleles (genes) may be responsible for aphid resistance in some accessions; thus, a new putative allele was identified in the Indian accession 90625, which exhibits a resistance phenotype slightly distinct from that mediated by the Vat allele.
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