Abstract
The basic leucine zipper (bZIP) transcription factor HY5 plays a multifaceted role in plant growth and development. Here the apple MdHY5 gene was cloned based on its homology with Arabidopsis HY5. Expression analysis demonstrated that MdHY5 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 MdMYB10 by binding to E-box and G-box motifs, respectively. Furthermore, we obtained transgenic apple calli that overexpressed the MdHY5 gene, and apple calli coloration assays showed that MdHY5 promoted anthocyanin accumulation by regulating expression of the MdMYB10 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 MdHY5 plays a vital role in anthocyanin accumulation and nitrate assimilation in apple.
Highlights
Apple (Malus × domestica) is an important fruit crop that is widely cultivated worldwide
Anthocyanins are synthesized via the phenylpropanoid pathway, and multiple enzymes are involved in this pathway, including phenylalanine ammonia lyase, chalcone isomerase, chalcone synthase, flavanone 3-hydroxylase (F3H), dihydroflavonol 4-reductase (DFR), UDP glucose: flavonoid 3-O-glucosyltransferase (UF3GT) and anthocyanidin synthase (ANS).[3,4]
Identification of the HY5 gene in apple Regarding the identification of the HY5 gene in the apple genome, the Arabidopsis HY5 gene was used as a query to search similar sequences in apple by mining the NCBI database with the Basic Local Alignment Search Tool (BLAST) program
Summary
Apple (Malus × domestica) is an important fruit crop that is widely cultivated worldwide. TFs are a group of key regulatory proteins that play important roles in controlling the expression of signal response genes. They can be divided into many families, such as the basic leucine zipper (bZIP), bHLH, MYB, zinc-finger and NAC families, according to their conserved domains. MdHY5 may be involved in anthocyanin biosynthesis by directly activating MdMYB10 and nitrogen signaling by promoting the expression of nitrate reductase (NR) genes and nitrate uptake genes. These results indicate that MdHY5 plays a vital role in anthocyanin accumulation and nitrate assimilation in apple.
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