Molecular heterogeneity of small subunit ADPglucose pyrophosphorylase cDNAs isolated from tuberous roots of sweet potatoes

Abstract

Four cDNAs (sT1, sT2, sT3 and sT4) encoding the small subunit of ADPglucose pyrophosphorylase (AGPase) were isolated from sweet potato tuberous roots. These cDNAs showed heterogeneity in nucleotide and amino acid sequences. In the protein coding sequences they showed a very high identity (>99%). But the sequences diverged in the 3′-UTRs of sT1 and sT2. The size of 3′UTRs were various in sT1, sT3 and sT4. The comparison of sT1 with a previously identified small subunit AGPase cDNA of sweet potatoes (SAPS) showed 91% identity at the nucleotide level and 96% identity at the amino acid level. Genomic southern analysis repealed that the small subunit AGPase polypeptide was encoded by multi-copy genes, suggesting the possibility that four isoforms originate from a different locus of sweet potato genome. With the level of nucleotide sequence conservation, the possible roles of various isoforms are discussed. The possible subgroups of isoforms are also discussed in terms of the level of nucleotide sequence conservation.