Identification of Mi-1 homologs in various Solanum species

Abstract

In Ecuador, several solanaceous crops, including naranjilla (Solanum quitoense), are attacked by the nematode Meloidogyne sp. Resistant cultivars are not available and there is a need to identify potential sources of resistance that can be incorporated into breeding programs. The Mi-1 gene from S. peruvianum is known to confer resistance to Meloidogyne in tomato (S. lycopersicum).
 In this study, 42 plant accessions of wild and cultivated Solanum species were screened to identify the presence of this gene, its diversification, expression, and evidence of gene recombination. The Mi-1 gene (exon 3) was identified in 34 accessions. Sixteen alleles were identified, that encode 15 different amino acid sequences, all of which encode NBS-LRR proteins and share 72-96 % homology with the tomato Mi-1 protein. The Mi-1 locus was highly polymorphic; most polymorphisms tend to accumulate in the NBS rather than in the LRR region. Genetic recombination was detected among the tomato and potato relate d sequences, but it was absent in the naranjilla group. Homologs identified expressed in both non-infected roots and leaves of some accessions, suggesting the constitutive expression of the gene.