Disequilibrium of Flavonol Synthase and Dihydroflavonol-4-Reductase Expression Associated Tightly to White vs. Red Color Flower Formation in Plants.

Huanan Jin,Manzhu Bao,Yuxiao Shen,Zhen Wang,Shasha Huang,Penghui Li,Jian Zhao,Ping Luo,Guogui Ning

doi:10.3389/fpls.2015.01257

Abstract

Flower color is the main character throughout the plant kingdom. Though substantial information exists regarding the structural and regulatory genes involved in anthocyanin and flavonol biosynthesis, little is known that what make a diverse white vs. red color flower in natural species. Here, the contents of pigments in seven species from varied phylogenetic location in plants with red and white flowers were determined. Flavonols could be detected in red and white flowers, but anthocyanins were almost undetectable in the white cultivar. Comparisons of expression patterns of gene related to the flavonoid biosynthesis indicated that disequilibrium expression of flavonol synthase (FLS) and dihydroflavonol-4-reductase (DFR) genes determined the accumulation of flavonols and anothcyanins in both red and white flowers of seven species. To further investigate the role of such common regulatory patterns in determining flower color, FLS genes were isolated from Rosa rugosa (RrFLS1), Prunus persica (PpFLS), and Petunia hybrida (PhFLS), and DFR genes were isolated from Rosa rugosa (RrDFR1) and Petunia hybrida (PhDFR). Heterologous expression of the FLS genes within tobacco host plants demonstrated conservation of function, with the transgenes promoting flavonol biosynthesis and inhibiting anthocyanin accumulation, so resulting in white flowers. Conversely, overexpression of DFR genes in tobacco displayed down-regulation of the endogenous NtFLS gene, and the promotion of anthocyanin synthesis. On this basis, we propose a model in which FLS and DFR gene-products compete for common substrates in order to direct the biosynthesis of flavonols and anthocyanins, respectively, thereby determining white vs. red coloration of flowers.

Highlights

Flavonoids are major secondary metabolites in plants including the flavonens, isoflavones, anthocyanins, flavones, and proanthocyanidins that provide plants with varied pigments (Dixon and Steele, 1999; Winkel-Shirley, 2001; Grotewold, 2006; Tanaka et al, 2008)
White and red flowers were characterized by significantly different levels of anthocyanin accumulation and this corresponded to marked differences in the ratio of anthocyanin and flavonol pigments in the two flower colors
The RrFLS1, PpFLS, and PhFLS genes were found to share striking sequence identity with flavonol synthase (FLS) sequences previously isolated from other plant species, with the middle portion of the encoded polypeptide sequence indicating strong sequence conservation

Summary

Introduction

Flavonoids are major secondary metabolites in plants including the flavonens, isoflavones, anthocyanins, flavones, and proanthocyanidins that provide plants with varied pigments (Dixon and Steele, 1999; Winkel-Shirley, 2001; Grotewold, 2006; Tanaka et al, 2008). Dihydroflavonol-4-reductase (DFR) controls one of the ratelimiting steps in the pathway and catalyzes the stereospecific reduction of three dihydroflavonols to leucoanthocyanidins (Martens et al, 2003; Shimada et al, 2005; Lo-Piero et al, 2006) This critical role of DFR in the flavonoid pathway is reflected in the focus of research programmes, and DFR gene homologs have been isolated from numerous plant species including Medicago truncatula (Xie et al, 2004), Lotus japonicas (Shimada et al, 2005), Camellia sinensis (Singh et al, 2009), and Populus trichocarpa (Huang et al, 2012)

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