Overexpression of and Transcription Factors from Pomegranate Enhances Freezing Tolerance in under the Promoter Activity Positively Regulated by PgICE1.

Cold stress limits plant growth, development and yields, and the C-repeat binding factors (CBFs) function in the cold resistance in plants. However, how pomegranate CBF transcription factors respond to cold signal remains unclear. Considering the significantly up-regulated expression of and in cold-tolerant 'Yudazi' in comparison with cold-sensitive 'Tunisia' under 4 °C, the present study focused on the two genes. PgCBF3 was localized in the nucleus, while PgCBF7 was localized in the cell membrane, cytoplasm, and nucleus, both owning transcriptional activation activity in yeast. Yeast one-hybrid and dual-luciferase reporter assay further confirmed that PgICE1 could specifically bind to and significantly enhance the activation activity of the promoters of and . Compared with the wild-type plants, the and transgenic lines had the higher survival rate after cold treatment; exhibited increased the contents of soluble sugar and proline, while lower electrolyte leakage, malondialdehyde content, and reactive oxygen species production, accompanying with elevated enzyme activity of catalase, peroxidase, and superoxide dismutase; and upregulated the expression of , , , and . Collectively, were positively regulated by the upstream PgICE1 and mediated the downstream genes expression, thereby enhancing freezing tolerance.