Establishment of esterase and peroxidase isozymes as genetic markers for a genetic linkage map of tuber-bearing Solanum

Genetic research on tuber-bearing Solanum (potato) has been limited by the scarcity of molecular markers and the lack of a genetic linkage map. Blocks of linked genes may be conserved during evolution of closely related species. Tomato (Lycopersicon) is a genera closely related to potato with a well-marked chromosome map. The hypothesis tested was that the chromosomes of tomato and potato contain conserved linkage groups for esterase and peroxidase isozyme genes. The following objectives were defined: (1) characterize and determine the homology of esterase and peroxidase isozymes for Solanum and Lycopersicon; (2) construct and test genetic models for inheritance of esterase and peroxidase isozymes and (3) localize esterase and peroxidase genes to a chromosome and/or establish linkages. The data from these objectives then established whether the genes controlling esterase and peroxidase isozymes are useful as genetic markers in diploid tuber-bearing Solanum.;Eight of the fourteen esterase and peroxidase loci in Lycopersicon had homology to isozyme loci in Solanum. One locus, Est2, was expressed in leaf tissue of both genera but no allelic variation was observed in the Solanum genotypes. The tuber-specific dimeric esterases of Solanum did not have complete homology with the dimeric esterases of other tissues from Lycopersicon. However, studies involving substrate specificity, isozyme inducibility and immunological assays provided evidence for possible homology between the dimeric esterase genes of the two genera. Based on these data, a genetic model was constructed for potato which consists of four tightly linked Est genes with multiple alleles. Three peroxidase loci, Prx1, Prx2 and Prx3, appeared to be homologous in the two genera and all encoded monomeric isozymes from multiple alleles. Alleles from two loci, Prx2 and Prx3, segregated concomitantly and are believed to be linked, but are independent of Prx1 and the tight linkage group of four Est loci. Thus, the two blocks of tightly linked genes have remained conserved between both genera.