The bZIP transcription factor MdHY5 regulates anthocyanin accumulation and nitrate assimilation in apple.

The basic leucine zipper (bZIP) transcription factor HY5 plays a multifaceted role in plant growth and development. Here the apple gene was cloned based on its homology with . Expression analysis demonstrated that transcription was induced by light and abscisic acid treatments. Electrophoretic mobility shift assays and transient expression assays subsequently showed that MdHY5 positively regulated both its own transcription and that of by binding to E-box and G-box motifs, respectively. Furthermore, we obtained transgenic apple calli that overexpressed the gene, and apple calli coloration assays showed that promoted anthocyanin accumulation by regulating expression of the gene and downstream anthocyanin biosynthesis genes. In addition, the transcript levels of a series of nitrate reductase genes and nitrate uptake genes in both wild-type and transgenic apple calli were detected. In association with increased nitrate reductase activities and nitrate contents, the results indicated that MdHY5 might be an important regulator in nutrient assimilation. Taken together, these results indicate that plays a vital role in anthocyanin accumulation and nitrate assimilation in apple.