Exploring the Molecular Mechanism of Blue Flower Color Formation in Hydrangea macrophylla cv. "Forever Summer".

Jiqing Peng,Chao Xue,Zhiming Liu,Fuxiang Cao,Xujie Dong

doi:10.3389/fpls.2021.585665

Abstract

Hydrangea macrophylla has a large inflorescence and rich colors, which has made it one of the most popular ornamental flowers worldwide. Thus far, the molecular mechanism of flower color formation in H. macrophylla flowers is unknown. By comparing the pigment content and transcriptome data of the bud period (FSF1), discoloration period (FSF2) and full-bloom stage (FSF3) of infertile blue flowers of H. macrophylla cv. “Forever Summer,” we found that genes associated with anthocyanin production were most associated with the formation of blue infertile flowers throughout development. The anthocyanin biosynthesis pathway is the main metabolic pathway associated with flower color formation, and the carotenoid biosynthesis pathway appeared to have almost no contribution to flower color. There was no competition between the flavonoid and flavonol and anthocyanin biosynthesis pathways for their substrate. At FSF1, the key genes CHS and CHI in the flavonoid biosynthesis pathway were up-regulated, underlying the accumulation of a substrate for anthocyanin synthesis. By FSF3, the downstream genes F3H, C3′5′H, CYP75B1, DFR, and ANS in the anthocyanin biosynthesis pathway were almost all up-regulated, likely promoting the synthesis and accumulation of anthocyanins and inducing the color change of infertile flowers. By analyzing protein–protein interaction networks and co-expression of transcription factors as well as differentially expressed structural genes related to anthocyanin synthesis, we identified negatively regulated transcription factors such as WER-like, MYB114, and WDR68. Their site of action may be the key gene DFR in the anthocyanin biosynthesis pathway. The potential regulatory mechanism of flower color formation may be that WER-like, MYB114, and WDR68 inhibit or promote the synthesis of anthocyanins by negatively regulating the expression of DFR. These results provide an important basis for studying the infertile flower color formation mechanism in H. macrophylla and the development of new cultivars with other colors.

Highlights

Hydrangea macrophylla is an shrub in the family Saxifragaceae
The carotenoid contents and the flavonoid contents decreased from FSF1 to FSF3, and the anthocyanin contents increased. This indicates that the blue infertile flower color formation process of H. macrophylla cv
We found that two MYB transcription factors and one WDR68 participated in the regulation of structural genes in the anthocyanin biosynthesis pathway (Figure 7)

Summary

Introduction

Hydrangea macrophylla is an shrub in the family Saxifragaceae. As many different species and cultivars are widely used as cut flowers, as potted plants, and in landscaping because of their large inflorescences and beautiful colors, H. macrophylla has become one of the most promising ornamental flower species. Plant color is mainly affected by anthocyanins (Zhao and Tao, 2015); their type and content are the most important factors affecting the formation of flower color (Dai, 2005; Han et al, 2008; Yamagishi et al, 2012). Pelargonin appears brick red, while cyanidin and peonidin appear purple-red; delphinidin, petunidin, and malvidin are instead between purple and blue These compounds can change the color of plants from pink to blueviolet (Kazuma et al, 2003; Wei et al, 2009). The formation of plant flower color is affected by both structural genes and transcription factors

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