Isolation of a MYB Transcription Factor Regulating Red Coloration of the Skin of Apple Fruit

The skin color of apple fruits is an important determinant of fruit quality.  The red coloration of the skin is attributed to accumulation of anthocyanins, belonging to a class of secondary metabolites in the flavonoid biosynthesis pathway, that are also potent antioxidants.  Fruit skin coloration is regulated mainly by transcription factors (TFs) present upstream of the anthocyanin biosynthesis cascade.  MYB transcription factors are known to play roles in the regulation mechanism in the upstream cascade.  It has been reported that transcription factors AtMYB11 and AtMYB12 in Arabidopsis influence expression of several genes in flavonoid biosynthesis, including CHALCONE SYNTHASE, CHALCONE ISOMERASE, FLAVONONE 3-HYDROXYLASE, and FLAVONOL SYNTHASE1.  An apple EST contig potentially encoding MdMYB11 has been identified by BLASTing an Arabidopsis AtMYB11 sequence against our apple EST database.  Specific primers are then designed based on the contig sequence, and used to screen an apple BAC library.  A total of six positive apple BAC clones have been identified and classified into two groups based on the size of PCR products. This indicated presence of more than a single copy of the AtMYB11 in the apple genome.  Two BAC clones, from different groups, have been picked, and subjected to subcloning to recover whole genomic DNA sequences.  Here, we report on the genomic structure of the apple MdMYB11 gene as well as its expression profile.