An isoform of sucrose synthase involved in sink strength of potato (Solanum tuberosum L.): Molecular cloning, sequence analyses, 3-D structure, crucial motifs and expression

Abstract

Sucrose synthase (SuSy, EC 2.4.1.13) refers to a glycosyltranferase (GT) that plays a crucial role in sugar metabolism mainly in the sink tissues of plants. Using uridine diphosphate (UDP) or adenosine diphosphate (ADP), SuSy catalyzes the reversible cleavage of sucrose into fructose, and UDP-glucose (UDP-Glc) or ADP-glucose (ADP-Glc), respectively. In plants, SuSy is encoded by relatively small gene families. It exists in multiple forms distributed differentially in the plant tissues suggesting their functional specializations. SuSy activity is regulated by a hierarchy of mechanisms including transcriptional control. Here, we report isolation and characterization of a 2,668-bp cDNA encoding a distinct full-length SuSy4 form, corresponding to SUS I group gene family, from a commercially important Indian potato (Solanum tuberosum L.) cultivar, Kufri Chipsona-1 by RT-PCR using tuber total RNA. The predicted protein consisted of 805 amino acids (designated KC-SuSy). All of the available potato SuSy proteins could be categorized into 3 groups i.e., SUS I−III as reported earlier in other plants. Phylogenetic analysis was carried out using the SuSy sequences from the potato, tomato and Arabidopsis. Multiple sequence alignments revealed segment-wise identity and divergence between the SuSy forms. Using KC-SuSy sequence, secondary structures, crucial domains/motifs and amino acids, and a three-dimensional (3-D) structure were predicted. KC-SuSy was found to be predominantly expressed in tuber. The early stages of tuber development were associated with high levels of SuSy activity. This report would be particularly useful for further studies on the SuSy proteins in potato and other Solanaceae family members.