A potato molecular-function map for carbohydrate metabolism and transport

Molecular-linkage maps based on functional gene markers (molecular-function maps) are the prerequisite for a candidate-gene approach to identify genes responsible for quantitative traits at the molecular level. Genetic linkag e between a quantitative trait locus (QTL) and a candidate-gene locus is ob served when there is a causal relationship between alleles of the candidate gene and the QTL effect. Functional gene markers can also be used for mark er-assisted selection and as anchors for structural and functional comparis ons between distantly related plant species sharing the same metabolic path ways. A first molecular-function map with 85 loci was constructed in potato based on 69 genes. Priority was given to genes operating in carbohydrate m etabolism and transport. Public databases were searched for genes of intere st from potato, tomato, or other plant species. DNA sequence information wa s used to develop PCR-based marker assays that allowed the localization of corresponding potato genes on existing RFLP linkage maps. Comparing the mol ecular-function map for genes operating in carbohydrate metabolism and tran sport with a QTL map for tuber starch content indicates a number of putativ e candidate genes for this important agronomic trait.