Transcriptome sequencing of purple petal spot region in tree peony reveals differentially expressed anthocyanin structural genes.

Yanzhao Zhang,Jianming Han,Yanwei Cheng,Shuzhen Xu,Huiyuan Ya

doi:10.3389/fpls.2015.00964

Abstract

The pigmented cells in defined region of a petal constitute the petal spots. Petal spots attract pollinators and are found in many angiosperm families. Several cultivars of tree peony contain a single red or purple spot at the base of petal that makes the flower more attractive for the ornamental market. So far, the understanding of the molecular mechanism of spot formation is inadequate. In this study, we sequenced the transcriptome of the purple spot and the white non-spot of tree peony flower. We assembled and annotated 67,892 unigenes. Comparative analyses of the two transcriptomes showed 1,573 differentially expressed genes, among which 933 were up-regulated, and 640 were down-regulated in the purple spot. Subsequently, we examined four anthocyanin structural genes, including PsCHS, PsF3′H, PsDFR, and PsANS, which expressed at a significantly higher level in the purple spot than in the white non-spot. We further validated the digital expression data using quantitative real-time PCR. Our result uncovered transcriptome variance between the spot and non-spot of tree peony flower, and revealed that the co-expression of four anthocyanin structural genes was responsible for spot pigment in tree peony. The data will further help to unravel the genetic mechanism of peony flower spot formation.

Highlights

Petal spot is a group of pigment cells restricted in defined region of petal
Our results showed that the four genes including PsCHS, PsF3 H, PsDFR, and PsANS showed significantly higher expression in spot than in non-spot
We found four key anthocyanin structural genes including PsCHS, PsF3 H, PsDFR, and PsANS were expressed at a significantly higher level in the red spot than in the white non-spot

Summary

Introduction

Petal spot is a group of pigment cells restricted in defined region of petal. It is widely distributed in the eudicots and the monocots, such as in Asteraceae, Brassicaceae, Geraniaceae, Ranunculaceae, Papaveraceae, Malvaceae, Scrophulariaceae, Iridaceae, Liliaceae, and Orchidaceae (Thomas et al, 2009). The spots attract pollinators (Eckhart et al, 2006; Goulson et al, 2009), and impart the ornamental value to the flower. Tree peony (Paeonia suffruticosa Andr.) – a woody shrub of the genus Paeonia and family Paeoniaceae – is a popular ornamental flower owing to its distinct petal colors. The pigmented cells on the corolla form petal spots and show more intense colors as compared with the background. In China, more than 1000 tree peony cultivars are mainly divided into four geographical groups including Xibei, Zhongyuan, Jiangnan, and Xinan groups (Zhang et al, 2007)

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Conclusion