Molecular cloning, sequence analyses, and expression studies of sucrose-phosphate synthase in potato (Solanum tuberosum L.) cultivars

Sucrose-phosphate synthase (SPS, EC 2.4.1.14) refers to a key enzyme in sucrose biosynthesis in both photosynthetic and nonphotosynthetic tissues of plants. It is encoded by different gene families. SPS exists in multiple forms which show differential distributions and functional specializations in the plant tissues. SPS activity is highly regulated by hierarchy of mechanisms including transcriptional control. Here, we report an isolation of a cDNA clone (3,591 bp) encoding full-length SPS A form consisting of 1,054 amino acids (designated KC-SPS1) from a commercially important Indian potato (Solanum tuberosum L.) cultivar, Kufri Chipsona-1 by RT-PCR approach from tuber total RNA. KC-SPS1 shared 99 % sequence identity with 1,053-amino acid SPS from potato cv. Desiree. Apart from some prominent amino acid substitutions, one extra Met residue at position 235 made KC-SPS1 a distinct member of SPS A family in potato. Full-length SPS sequences from taxonomically different plant species were used in making a phylogenetic tree which showed both evolutionary relatedness, and also their grouping into different SPS families. Hydropathy characters and secondary structures were predicted in various SPS forms. Sequence analyses and comparison of the SPS sequences from the Solanaceae family members revealed many distinct features within and between the SPS gene families which were not documented earlier. SPS A form-specific expression patterns were studied in the leaves and tubers of different potato cultivars based on semi-quantitative RT-PCR and protein blot analyses. SPS activities particularly in the cold-stored tubers were probably due to altered kinetic properties. This report would be useful for in-depth studies on various SPS isoforms in potato and other Solanaceae family members.