Amylase Inhibitor SbAI in Potato Species: Structure, Variability and Expression Pattern

Starch degradation in plants is mediated by amylases, the activity of which is post-translationally regulated by inhibitors. It is assumed that the SbAI amylase inhibitor activity is associated with potato cold stress resistance. The study of possible correlations of the SbAI variability with the cold resistance of potato species will improve the understanding of the starch metabolism regulation during plant development and stress response. In the present study, the genome sequences homologous to SbAI were identified in 12 potato species of section Petota. In total, 36 allelic variants of the gene and 31 variants of the protein were revealed. Comparison with data on S. tuberosum cultivars showed that the SbAI cultivar polymorphism is 1.4–1.7 times higher than the interspecific, but the species possess a larger number of allelic variants. Phylogenetic analysis revealed that, for S. demissum , S. acaule , and S. stoloniferum , each species SbAI allelic variants did not get into one clade. The SbAI gene expression pattern was determined in various organs of the species S. tuberosum (cv. Nadezhda), S. rybinii , S. chacoense , and S. kurtzianum . In leaves, S. chacoense SbAI expression level was 13, 50, and 250 times higher than in S. tuberosum , S. kurtzianum , and S. rybinii , respectively. Varied levels of SbAI expression in the species may be due to different initial contents of both synthesized starch and reducing sugars in the leaves. In tubers, S. tuberosum SbAI expression was 5.2, 8.6, and 430 times higher than in S. kurtzianum , S. chacoense , and S. rybinii . In roots, S. rybinii SbAI expression was 2.4 times higher than in S. chacoense and 42.3 times higher than in S. kurtzianum and S. tuberosum . The absence of correlation between the SbAI expression level and the species cold resistance was shown. The obtained expression data suggest that different potato species and cultivars may differently regulate tuber starch content.