Molecular studies on the starch granule bound protein R1 protein and genetic approaches for its inhibition in the potato tubers

Abstract

The potato (Solanum tuberosum L.) is one of the most important food crops capable of nourishing the world s vast population. Starch is the major component of the dry matter accounting for approximately 70% of the total solids. The other components include total sugars, proteins, fibres, lipids, riboflavin, niacin, vitamin A, vitamin C, minerals, ash and very small amount of glycoalkaloids. Potato plant is an important model crop both in terms of basic and applied research. Starch is synthesized in the amyloplasts of potato tubers. It comprises linear (amylose, approx. 25-30%) and branched (amylopectin, approx. 70-80%) glucose polymers arranged in to highly ordered, semicrystalline structures-the starch granule. Starch phosphorylation is an important aspect of starch metabolism. The level of starch phosphorylation usually varies between the starches from different plant species. Approximately 60-70% of the phosphate groups are linked to C-6 of the glucose residues, the rest to C-3 positions of glucosyl residues, and only 1% may be linked to C-2. In potato tuber starch, approx. 0.1-0.5% of the glucose moieties is found to be phosphorylated. It is commonly accepted that starch phosphorylation influences the overall secondary structures of the starch granule-a prerequisite for its degradation. There is a growing interest on the isolation and characterization of R1 protein i.e. and#61537;-glucan/glucan-like, water dikinase (GWD) from different plant species. Since GWD is known to catalyze starch phosphorylation both in leaves and different plant storage organs. In the present study, a 4789-bp full-length cDNA (submitted to the NCBI data base under GenBank Acc No EU599037) encoding a GWD isoform was isolated from a commercially important Indian potato cultivar, Kufri Chipsona-1 by RT-PCR approach using tuber RNA.