Transcriptional control of anthocyanin biosynthetic genes in the Caryophyllales

Anthocyanins and betacyanins, two types of red pigment, have never been found to occur together in plants. Although anthocyanins are widely distributed in higher plants, betacyanins have replaced anthocyanins in the Caryophyllales. The accumulation of flavonols in the Caryophyllales suggests that the step(s) of anthocyanin biosynthesis from dihydroflavonols to anthocyanins could be blocked in the Caryophyllales. Dihydroflavonol 4-reductase (DFR) and anthocyanidin synthase (ANS) cDNAs were isolated from plants of the Caryophyllales. An enzyme activity assay showed that the Caryophyllales possess functional DFR and ANS. The expression profile revealed that DFR and ANS are not expressed in most tissues and organs except the seeds in Spinacia oleracea. Here, the promoter regions of DFR and ANS were isolated from S. oleracea. Analysis of DFR and ANS promoter sequences revealed several putative transcriptional factor-binding motifs. A yeast one-hybrid assay showed that Petunia hybrida AN2 (PhAN2) and JAF13 (PhJAF13), which were the regulators of anthocyanin synthesis in P. hybrida, could bind to the S. oleracea DFR and ANS promoters. However, the transient assay in Phytolacca americana cell cultures and leaves of S. oleracea showed that the promoters were not activated by ectopic expression of PhAN2 and PhJAF13, while the DFR and ANS promoters of Arabidopsis thaliana, an anthocyanin-producing species, were activated. One possible explanation for the lack of anthocyanins in the Caryophyllales is the difference in the promoter regions of DFR and ANS compared with those of anthocyanin-producing species.