Allele and isozyme patterns of UDP-glucose pyrophosphorylase as a marker for cold-sweetening resistance in potatoes

Uridine-5-'diphosphoglucose pyrophosphorylase (UTP alpha -D-glucose-1-phosphate uridylyltransferase, E.C. 2.7.7.9) (UGPase) was cloned from 16 potato cultivars (Solanum tuberosum L.) that differed in their ability to accumulate reducing sugars in cold storage (3 C) using RT-PCR. Two UGPase-alleles designated as UgpA (minus a BamH1 site) and UgpB (containing one BamH1 site), were present in most cultivars. Cultivars that were cold-resistant (CR) to sweetening demonstrated an UgpA:UgpB ratio favoring the UgpA allele (4:0 or 3:1), while cultivars that were cold-sensitive CCS) exhibited a predominance for the UgpB allele (1:3 or 0:4). Following cold-storage at 3 C for two months, the CR and CS clones accumulated 10.3 +/- 2.1 and 31.2 +/- 2.2 mu mol glucose/g Fm: respectively. The glucose content and chip color between the CR and CS clones were significantly different at the 99% level of confidence. Staining for UGPase activity in nondenaturing polyacrylamide gels of proteins extracted hom CS potatoes revealed up to three acidic isozymes of UGPase (i.e., UGP1, UGP2, UGP3) with UGP3 being the most abundant. Activity staining using CR cultivars demonstrated two additional isozymes of UGPase with greater electrophoretic mobility (more basic in charge) which mere designated UGP4 and UGP5. The potential for using UGPase allelic ratios and/or UGPase isozymic patterns as a selective tool to screen segregating progeny in a potato breeding program for cold-sweetening-resistant germplasm is discussed.