Coordinate expression of genes involved in catechin biosynthesis in Polygonum hydropiper cells

Abstract.

Suspension-cultured cells of Polygonum hydropiper contain a high level of catechins (H cells), unlike tissues of the parental plants, which express a low level. A cell line (L cells) containing a tenfold lower level of catechins than H cells was isolated from H cells. To determine the mechanism regulating catechin biosynthesis, we have investigated the expression of genes involved in flavonoid biosynthesis in these two cell lines. Deduced amino acid sequences of the gene fragments encoding chalcone synthase, flavanone 3-hydroxylase and dihydroflavonol 4-reductase isolated from H cells showed a high similarity to those from other plants. Genomic Southern analysis indicated that there is no difference in the restriction patterns of these gene fragments between the two cell lines and seedlings. Throughout the culture period, all of the genes in the H cells were highly expressed, while those in the L cells were repressed. In the seedlings, all of the genes were expressed in a light-dependent fashion, while in H cells these genes were highly expressed regardless of the presence or absence of illumination. These findings indicate that the genes involved in catechin biosynthesis are coordinately regulated at the transcriptional level.