Flower color is a defining trait in ornamental plants, yet the genetic control of subtle background pigmentation remains poorly understood. In flare tree peony (Paeonia rockii), previous research has focused primarily on the dramatic basal flare, leaving the regulation of uniform petal background color unclear. This study identifies a novel transcriptional module, PrFRS2–PrMYB75a, that governs purple background coloration. The MYB transcription factor PrMYB75a directly activates key anthocyanin biosynthetic genes, while the upstream regulator PrFRS2 enhances pigment accumulation both indirectly through PrMYB75a and directly by targeting structural genes. Together, this regulatory hierarchy drives anthocyanin accumulation and shapes petal coloration patterns.
Anthocyanins are the principal pigments responsible for red, purple, and blue hues in most flowering plants. In tree peonies, floral coloration has been linked to structural genes in the anthocyanin biosynthesis pathway and their regulation by MYB transcription factors. In Paeonia rockii, however, most studies have concentrated on the formation of the dark basal flare at the petal base. The molecular mechanisms controlling the broader, uniform background color remain largely unexplored. Although structural genes such as CHS and ANS are conserved, differences in petal color are unlikely to result solely from coding sequence variation. Based on these challenges, it is necessary to conduct in-depth research into the transcriptional regulatory network underlying petal background coloration.
Researchers from Beijing Forestry University report, in a study published (DOI: 10.1093/hr/uhaf288) in Horticulture Research (2025), the identification of a transcriptional module that regulates petal background coloration in flare tree peony (Paeonia rockii). By comparing purple and white cultivars, the team discovered a key MYB transcription factor, PrMYB75a, and its upstream regulator PrFRS2, which together control anthocyanin accumulation. Through transcriptome analysis, transgenic validation in Arabidopsis thaliana and Nicotiana tabacum, gene silencing experiments, and molecular interaction assays, the researchers uncovered the hierarchical regulatory mechanism determining whether petals develop a purple background.
To clarify the determinants of background coloration, the researchers compared two cultivars: purple 'Jing Hong' and white 'Jing Yu Dan'. Biochemical analyses showed that purple petals accumulated cyanidin, peonidin, and pelargonidin derivatives, while white petals contained negligible anthocyanins. Peonidin 3,5-di-O-glucoside was identified as the predominant pigment. Transcriptome comparisons revealed 14 anthocyanin pathway–related genes significantly upregulated in purple petals. Among them, the R2R3-MYB transcription factor PrMYB75a exhibited more than 100-fold higher expression at the onset of pigmentation. Overexpression of PrMYB75a in Arabidopsis thaliana and Nicotiana tabacum resulted in enhanced anthocyanin accumulation and intensified pigmentation, while virus-induced gene silencing in peony petals reduced anthocyanin levels by over 80%, confirming its activating role. Yeast one-hybrid, dual-luciferase reporter, and electrophoretic mobility shift assays demonstrated that PrMYB75a directly binds MYB-recognition motifs in the promoters of PrCHS1 and PrANS, activating their transcription. Further screening identified PrFRS2, a FAR1-related transcription factor, as an upstream regulator. PrFRS2 binds directly to the promoter of PrMYB75a, activating its expression. Additionally, PrFRS2 directly binds the promoter of PrANS, establishing a dual regulatory pathway that amplifies anthocyanin biosynthesis.
"Our study reveals a previously uncharacterized regulatory module controlling petal background coloration in Paeonia rockii," the corresponding author stated. "Unlike basal flare formation, which depends on spatially restricted MYB expression, uniform background coloration is governed by coordinated activation of anthocyanin genes through PrFRS2 and PrMYB75a. This hierarchical control mechanism highlights how transcription factors integrate regulatory signals to shape floral pigmentation." The identification of an FRS-family transcription factor directly involved in flower color regulation also expands current understanding of anthocyanin regulatory networks in ornamental plants.
The discovery of the PrFRS2–PrMYB75a module provides precise molecular targets for improving flower color traits in tree peony breeding programs. By manipulating the expression of these transcription factors, breeders may achieve stable and predictable modifications in petal background coloration. Because FRS-family transcription factors are often responsive to environmental cues such as light and temperature, this module may also link environmental signals to pigment accumulation, offering strategies to maintain ornamental quality under variable growing conditions. Beyond tree peony, these findings contribute to broader insights into hierarchical transcriptional regulation, floral pattern diversification, and precision breeding in ornamental and horticultural crops.
