Pyrophosphorylases in potato. V. Allelic polymorphism of UDP-glucose pyrophosphorylase in potato cultivars and its association with tuber resistance to sweetening in the cold.

UDP-glucose pyrophosphorylase (UGPase) was cloned from six American and nine European potato (Solanum tuberosum L.) cultivars. Restriction mapping of the different UGPase-cDNAs with BamHI, HindIII, and EcoRI revealed that at least two mRNA populations were present in most cultivars. Staining for UGPase activity in nondenaturing gels of proteins extracted from developing potato tubers yielded two major isozymes that were highly active and appeared to be dimeric in nature. Following sodium dodecyl sulfate-polyacrylamide gel electrophoresis, all isozymes were disassociated into a single subunit with a molecular mass of 53 kD. Since UGPase has been demonstrated to be a single-copy gene in the haploid genome of potato (A.Y. Borovkov, P.E. McClean, J.R. Sowokinos, S.H. Ruud, G.A. Secor [1995] J Plant Physiol 147: 644-652), there must be allelic differences at the UGPase locus (chromosome 11). The two alleles, designated ugpA and ugpB, were identified by the absence and presence of a BamHI site, respectively. The relative band intensities of the two cDNA populations following polymerase chain reaction amplification and agarose gel electrophoresis were related to a potato cultivar's ability to resist sweetening when exposed to cold temperatures.