Complex regulation of the TaMyc1 gene expression in wheat grain synthesizing anthocyanin pigments.

The wheat TaMyc1 gene encodes for transcriptional factor (TF) with bHLH domain. The gene is expressed in purple wheat grains and activates transcription of the anthocyanin biosynthesis structural genes. To reveal the features of TaMyc1 regulation in wheat pericarp transcription start sites (TSS) were identified by 5' RACE mean and translation efficiency was predicted by in silico methods. Three alternative transcript variants of TaMyc1 differing by 5' leader sequence only were identified in purple pericarp. The three transcripts are generated from distinct TATA boxes and thereby are differed by TSS. Two transcripts (TaMyc1a, -b) have identical initiation AUG codons that lead to the TaMYC1 regulatory protein with bHLH domain. However because of different stability of secondary structures predicted in 5' leader the two transcripts might be translated with different efficiency. The third transcript is assumed to be not effectively translated. qRT-PCR and colonies counting were applied to assess contribution each of the transcripts to total TaMyc1 gene transcription level. TaMyc1c has the lowest contribution (ca. 16%), whereas the others two transcripts contribute equally (ca. 42%) to total TaMyc1 expression level. The role of the tree mRNA isoforms transcribed in one tissue is discussed.