Expression of the а-amylase gene Stamy23 in photosynthetic and non-photosynthetic tissues of potato (Solanum tuberosum L.) cultivars

Potato ( Solanum tuberosum L.) is the fourth most important agricultural crop after cereals. Almost every tissue of a potato plant contains starch, the regulation of metabolism and the physiological role of which depends on the type of tissue, the stage of plant development and external factors. Starch hydrolysis is catalyzed by α- (AMY) and β- (BAM) amylases. By degradation of cytosolic phytoglycogen, StAmy23 amylase regulates tuber cold-induced sweetening and physiological dormancy. Few available studies on StAmy23 have focused on gene activity in potato tubers, including in response to cold stress. In this study, StAmy23 expression pattern in photosynthetic and non-photosynthetic tissues of potato plants of three cultivars, differing in starch content in tubers, was determined for the first time. Structural and phylogenetic analyses revealed that the closest homologs of StAmy23 are the α-amylases of various potato and tomato cultivars. Analysis of the carbohydrate content in freshly harvested tubers of the studied potato cultivars showed a similar high starch content for cv. Gala and cv. Saturna and almost 2 times lower for cv. Barin (6.3 vs. 11.34 mg/g of tissue). The largest amount of reducing sugars was found in tubers of cv. Saturna; cv. Gala tubers contained 4.5 and 24.5 times less of glucose/fructose than cv. Barin and cv. Saturna tubers, respectively (0.016/0.000 vs. 0.056/0.016 and 0.217/0.175 mg/g of tissue). For the first time, the expression profile of StAmy23 was determined not only in tubers, leaves and stems, but also in other organs and tissues of the potato plant. A high level of gene expression in stems and fruits was shown. In non-photosynthetic roots and stolons, StAmy23 transcription level either corresponded (cv. Saturna) or significantly exceeded (cv. Barin, cv. Gala) that in tubers. In stems, the highest and lowest StAmy23 transcription levels were observed in cv. Gala and cv. Saturna, respectively (0.58 and 0.13). Leaves and tuber peels showed similar, relatively low levels of StAmy23 expression. In fruits, the highest StAmy23 expression was found in cv. Barin (0.29), in the roots and tubers - in cv. Gala (0.55 and 0.17), and in the stolons - in cv. Barin and cv. Gala (0.31 and 0.33). A positive association was proposed between the level of StAmy23 transcription and the starch content (but not the content of reducing sugars) in tubers. The transcriptional activity of the StAmy23 gene in photosynthetic tissues of potato plants suggests the participation of encoded α-amylase in starch hydrolysis not only in storage organs, but also in vegetative organs to maintain physiological growth processes and plant stress response.