Abstract
BackgroundThe tree peony (Paeonia suffruticosa Andr.) cultivar ‘Er Qiao’ is appreciated for its unstable variegated flower coloration, with cyanic and acyanic flowers appearing on different branches of the same plant and occasionally in a single flower or petal. However, the variegation mechanism is still unclear.ResultsIn this study, we found significantly higher contents and more diverse sets of anthocyanins in the cyanic petals than in the acyanic petals. Comparative transcriptome analysis between the two flower types revealed 477 differentially expressed genes (DEGs). Quantitative real-time PCR results verified that the transcript levels of the flavonol synthase (FLS) gene were significantly increased in the acyanic petals. Furthermore, we found that a GCGGCG insertion at 246 bp in the flavonoid 3′-hydroxylase (F3’H) gene-coding region constitutes a duplication of the 241–245 bp section and was consistently found only in acyanic flowers. Sequence alignment of the F3’H gene from different plant species indicated that only the acyanic petals of ‘Er Qiao’ contained the GCGGCG insertion. The transformation of Arabidopsis tt7–1 lines demonstrated that the ectopic expression of F3’H-cyanic, but not F3’H-acyanic, could complement the colors in the hypocotyl and seed coat.ConclusionIn summary, we found that an indel in F3’H and the upregulation of FLS drastically reduced the anthocyanin content in acyanic petals. Our results provide molecular candidates for a better understanding of the variegation mechanisms in tree peony.
Highlights
The tree peony (Paeonia suffruticosa Andr.) cultivar ‘Er Qiao’ is appreciated for its unstable variegated flower coloration, with cyanic and acyanic flowers appearing on different branches of the same plant and occasionally in a single flower or petal
Anthocyanin composition in ‘Er Qiao’ flowers High-performance liquid chromatography (HPLC) analysis was used to investigate the differences in anthocyanin content of different flower parts (Fig. 2)
In the acyanic petals, the significantly increased activity of flavonol synthase (FLS) may result in the diversion of the substrate dihydrokaempferol to form flavonols
Summary
The tree peony (Paeonia suffruticosa Andr.) cultivar ‘Er Qiao’ is appreciated for its unstable variegated flower coloration, with cyanic and acyanic flowers appearing on different branches of the same plant and occasionally in a single flower or petal. Due to its high ornamental value, tree peony is considered an important horticultural flower in China. Flower color variegation is usually associated with differences in anthocyanin content. The gene mutations associated with flower variegation have been investigated in many plants, and research suggests that a transposable element insertion in the genes associated with anthocyanin synthesis, transport, or regulation is largely responsible [16,17,18]. A small indel in an anthocyanin transport gene was found to lead to variegated coloration in peach flowers [21]
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