Epigenetic regulation of dihydroflavonol reductase in petunia and sensitivity of chalcone synthase promoter to RNA dependent DNA methylation

Abstract

Petal colour is an excellent marker to study regulation of dihydroflavonol 4-reductase (DfrA) and chalcone synthase (Chs) involved in plant pigment biosynthesis. Still, alternative regulation of genes without altering their primary DNA sequences is still developing. In this study, fragments of DfrA promoter and coding region were transformed and tested for activity in petunia (Petunia hybrida) severely methylated in the promoter. On the other hand, we examined if inverted repeat construct of ChsA promoter is sufficient to methylate homologous sequences to induce silencing in petunia. We report that W80 petunia lines having W4 constructs produced flowers with pink petals. Stunted growth, delayed maturation and patched yellow coloration of leaves were evident in V26 lines transformed with V2, though the plants did not yet flower by the end of the study period. However, all V26 lines with V4 produced flowers with purple petals. It was unexpected to note that W80 plant lines with V4 produced white flowers. The fact that W80 plant lines with W4 produced purple flowers suggests that both the transgene and DfrA promoter may have been active in a white petal plant. The results suggest that the promoter was active to drive the expression of pigmentation genes.

Keywords: petunia, DNA methylation, Agrobacterium tumefaciens, chalcone synthase, dihydroflavonol 4-reductase