Cloning of potato transcription factor StBBX21 and functional verification under drought and salt stress tolerance

The B-box (BBX) gene family plays a vital role in regulating various physiological and developmental processes of plants and in mediating stress responses, and it is one of the most important transcription factors in plants. As the important economic crops in China, potato (Solanum tuberosum) has the characteristics of low input and high yield, but the potential function of BBX gene in potato under drought and salt stress is still unclear. In this study, the StBBX21 gene was cloned from potato, and its bioinformatic characteristics and expression pattern were analyzed. The function of StBBX21 was verified by subjecting StBBX21-overexpressing transgenic potato plants to drought and salt stress treatments. The results indicated that the CDS of StBBX21 was 897 bp in length, encoding 298 amino acids. It was a hydrophilic protein with two B-box domains. Multiple light-responsive and hormone-responsive elements were identified in the promoter region of StBBX21. The expression pattern analysis showed that the expression level of StBBX21 gene in different tissues of potato followed the order tuber > stem > leaf, and the gene was significantly induced under drought and salt stress. Compared with wild-type, StBBX21-overexpressing potatoes exhibited significantly lower relative conductivity and malondialdehyde (MDA) content, while the contents of free proline (Pro), soluble proteins, and soluble sugars, as well as the activities of peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT) were significantly increased under drought and salt stress. Furthermore, the expression of several stress-related genes was significantly up-regulated. The results illustrated that overexpression of StBBX21 enhanced drought tolerance and salt tolerance of potato by regulating physiological adaptation and stress-related gene networks. This finding provides a reference for further study of the potato BBX family and enriches the understanding of the molecular mechanism of potato stress resistance.