Allele variability of amylase inhibitor gene AI in potato varieties and lines

The economic efficiency of potato varieties includes not only yield characteristics, but also taste preservation during storage. Storing potato tubers at low temperatures leads to the degradation of starch and the accumulation of reducing sugars; the latter during heat treatment contribute to the deterioration of taste and participate in acrylamide synthesis. Starch degradation to simpler compounds is achieved in two pathways: hydrolytic and phosphorolytic. In the hydrolytic pathway, hydrolases, including a- and b-amylase, are responsible for cleavage of starch, and exhibit different activities depending on the tissue, organ type, cell localization, and plant species. Amylase activity is regulated at the post-translational level by an amylase inhibitor (AI), which binds amylase and blocks the active site of the enzyme, or changes its conformation, thereby reducing the catalytic activity. Although AI role in plant is very important, present data on the AI genes and encoded proteins in representatives of the genus Solanum are extremely limited. In this study, AI sequences were obtained and analyzed in 36 potato varieties and lines of domestic and foreign selection. Two types of AI coding sequence were identified, 621 and 630 bp, depending on presence of 9-bp insert GGTGCAWTT at the 3´-end of the cDNA. The analyzed gene was characterized by an extremely high polymorphism level: exonic sequences contained 134 SNPs (singe nucleotide polymorphisms) (21.3 %), which resulted in 69 amino acid substitutions (33.0 %) in the encoded proteins. Detected GAI/F202 insertion in the C-terminal region of some AI proteins resulted from the 9-bp 3´-gene insertion. Among the 69 amino acid substitutions identified, only 11 are radical and may lead to a change in the protein conformation. All of the analyzed potato accessions were heterozygous and possessed several allelic variants of the gene. In total, 70 allelic variants of the gene and 69 associated protein variants are identified. The largest number of single nucleotide polymorphisms is among the allelic variants of the gene in the varieties Lux (18 substitutions), Irbitskii (17 substitutions) and Gala (16 substitutions). The largest number of amino acid substitutions is in the AI proteins in the Gala (9 substitutions) and Gornyak (8 substitutions) varieties.