Characterization of PAP1-upregulated Glutathione S-transferase genes in Arabidopsis thaliana

Glutathione S-transferase (GST) plays an important role in the transport and accumulation of anthocyanin and proanthocyanidin in plants. In our previous study on Arabidopsis thaliana overexpressing the PRODUCTION OF ANTHOCYANIN PIGMENT 1 (PAP1) gene encoding an MYB transcription factor, the AtGSTF5 and AtGSTF6 genes encoding GST-like protein were up-regulated along with TRANSPARENT TESTA 19 (TT19), which is required for the accumulation of anthocyanin and proanthocyanidin. The proteins encoded by these 3 genes showed very weak GST activities as detected by using recombinant proteins expressed in Escherichia coli. The anthocyanin levels were severely decreased in the tt19 mutant but not in the Atgstf6 mutant, suggesting that TT19 is almost exclusively involved in anthocyanin accumulation. The results of co-expression network analysis using public transcriptome data corresponded to the proposition of the predominant role of TT19 in anthocyanin accumulation.