Expression analysis of anthocyanin biosynthesis key regulatory genes involved in pomegranate ( Punica granatum L.)

Pomegranate (Punica granatum L.) is one of the oldest and important horticultural plants in Iran. Pomegranate fruits are an important source of secondary metabolites such as phenolic compounds, tannins, colors and alkaloids. Anthocyanin accumulation in plant organs is associated with gene expression in anthocyanin biosynthesis pathway. Regulation of anthocyanin biosynthesis expression is controlled by a number of transcription factors including MYB, basic helix–loop–helix (bHLH) and WD-repeat protein (WD-Repeat) proteins. In order to study the expression level of some transcription factors/genes and their role in pomegranate skin color, real time PCR analysis was used to assess the expression patterns among different pomegranate genotypes. Results of this study showed that white and green skin genotypes had the highest AN1 (bHLH) expression, whereas bright red and black skin genotypes accumulated the lowest AN1 transcript level. Furthermore, green and bright red genotypes showed the highest and the lowest expression level with regard to AN2 (MYB) transcription factor, respectively. The DFR gene expression in samples with black skin was the highest while in white skin samples the lowest expression of this gene was shown. This result indicates the influence of WD40 transcription factor on DFR structural gene and its effective role on synthesis of skin color. With regard to expression of three transcription factors in all genotypes, it was evident that MYB–bHLH–WD40 complex confers the skin color in pomegranate. Total anthocyanin content measurement showed a positive correlation between the level of DFR gene expression and accumulation of anthocyaninsin different genotypes.