Anthocyanin Genes Involved in the Flower Coloration Mechanisms of Cymbidium kanran.

Zhuang Zhou,Zhen Ying,Yanping Yang,Wan Xu,Siren Lan,Zhongjian Liu,Shuangbin Fu,Xiaole Wang,Lijuan Yao,Aiping Zeng,Zhigang Wu,Jian Huang

doi:10.3389/fpls.2021.737815

Abstract

The Orchidaceae, otherwise known as orchids, is one of the largest plant families and is renowned for its spectacular flowers and ecological adaptations. Various polymorphisms of orchid flower colour can attract pollinators and be recognised as valuable horticultural ornamentals. As one of the longest historic cultured orchids, Cymbidium kanran has been domesticated for more than 2,500 years and is an ideal species to study coloration mechanisms because of plentiful variations in floral coloration and abundant traditional varieties. In this study, we used two distinct colour-type flowers of C. kanran as experimental materials to elucidate the mechanism of flower coloration. High-performance liquid chromatography (HPLC) analysis revealed that anthocyanins in purple-red-type flowers include three types of anthocyanidin aglycones, peonidin, malvidin, and cyanidin, whereas anthocyanins are lacking in white-type flowers. Through comparative transcriptome sequencing, 102 candidate genes were identified as putative homologues of colour-related genes. Based on comprehensive correlation analysis between colour-related compounds and gene expression profiles, four candidates from 102 captured genes showed a positive correlation with anthocyanidin biosynthesis. Furthermore, transient expression of CkCHS-1, CkDFR, and CkANS by particle bombardment confirmed that recovery of their expression completed the anthocyanin pathway and produced anthocyanin compounds in white-type flowers. Collectively, this study provided a comprehensive transcriptomic dataset for Cymbidium, which significantly facilitate our understanding of the molecular mechanisms of regulating floral pigment accumulation in orchids.

Highlights

Orchids are important ornamental plants characterised by their fantastic floral morphology and high levels of corolla-colour polymorphism and variability, which have played an important role in pollination and have excited biologists since Darwin (Gigord et al, 2001; Aguiar et al, 2020; Basist et al, 2021)
The white and purple-red phenotype C. kanran flowers had provided a unique experimental system to examine the mechanism for flower anthocyanin pigmentation
Purple-red flowers are comprised of three types of anthocyanidin compounds, namely, peonidin, malvidin, and cyanidin, which were shown by High-performance liquid chromatography (HPLC) analysis

Summary

Introduction

Orchids are important ornamental plants characterised by their fantastic floral morphology and high levels of corolla-colour polymorphism and variability, which have played an important role in pollination and have excited biologists since Darwin (Gigord et al, 2001; Aguiar et al, 2020; Basist et al, 2021). The mechanism of genes encoding enzymes for flower coloration in orchids has been studied in some species (Mudalige-Jayawickrama et al, 2005; Han et al, 2006; Hieber et al, 2006; Chen et al, 2011; Hsiao et al, 2011; Liu et al, 2012; Yu et al, 2018), as one of the longest historic floricultural plants, Cymbidium kanran attracts wide attention. Anthocyanins, as a series of secondary metabolites, are water-soluble pigments that contribute colours from orange, pink, red, magenta, purple, blue, cyan to “black” (Hatier and Gould, 2007; Tanaka et al, 2008; Petroni and Tonelli, 2011; Moreau et al, 2012; Li et al, 2014). Delphinidin, pelargonidin, and cyanidin, undergo several modifications, such as glycosylation or methylation, by UDP-glucoside: flavonoid 3-O-glucosyltransferase (3GT) and anthocyanin methyltransferase (AMT)

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Results

Conclusion