Integrated transcriptomic and metabolomic analyses reveal the mechanisms underlying flower colour change from green to white in tree peony

Abstract

Tree peonies with green flowers are rare, because they appear green at the initial blooming stage (CH) but turn white at the full blooming stage (SH). As limited information is available on the mechanisms underlying flower colour change in tree peonies, we performed transcriptomic and metabolomic analyses using the petals of Paeonia suffruticosa cultivar ‘Lvmuyinyu’ at the CH and SH stages. During flower development and blooming, flower colour changed from green to white, and the chlorophyll and anthocyanin content in the petals decreased sharply. The expression levels of chlorophyll synthesis genes and degradation genes were consistent with changes in the chlorophyll and anthocyanin levels. Upon non-target metabolomic analysis, a total of 86 differentially expressed metabolites related to flower colour change were identified. These metabolites were mainly involved in anthocyanin, secondary metabolite, flavonoid, and flavonol biosynthesis. We also identified 1318 differentially expressed genes (DEGs), of which 821 DEGs were upregulated and 497 were downregulated; and 12 differentially expressed MicroRNAs (DEMs), of which 2 were downregulated and 10 were upregulated. Functional analysis revealed that the targets of these DEGs and DEMs were primarily enriched in plant hormone signal transduction, starch and sucrose metabolism, endocytosis, and ether lipid metabolism. Integrated analysis of DEG and DEM profiles predicted nine miRNA–mRNA pairs, suggesting that these regulatory factors may be involved in flower colour change in tree peony. These findings are significant for the directional improvement of flower colour and the cultivation of new tree peony cultivars.