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BackgroundPlants have remarkable diversity in petal colour through the biosynthesis and accumulation of various pigments. To better understand the mechanisms regulating petal pigmentation inLonicera japonica, we used multiple approaches to investigate the changes in carotenoids, anthocyanins, endogenous hormones and gene expression dynamics during petal colour transitions, i.e., green bud petals (GB_Pe), white flower petals (WF_Pe) and yellow flower petals (YF_Pe).ResultsMetabolome analysis showed that YF_Pe contained a much higher content of carotenoids than GB_Pe and WF_Pe, with α-carotene, zeaxanthin, violaxanthin and γ-carotene identified as the major carotenoid compounds in YF_Pe. Comparative transcriptome analysis revealed that the key differentially expressed genes (DEGs) involved in carotenoid biosynthesis, such asphytoene synthase,phytoene desaturaseandζ-carotene desaturase, were significantly upregulated in YF_Pe. The results indicated that upregulated carotenoid concentrations and carotenoid biosynthesis-related genes predominantly promote colour transition. Meanwhile, two anthocyanins (pelargonidin and cyanidin) were significantly increased in YF_Pe, and the expression level of ananthocyanidin synthasegene was significantly upregulated, suggesting that anthocyanins may contribute to vivid yellow colour in YF_Pe. Furthermore, analyses of changes in indoleacetic acid, zeatin riboside, gibberellic acid, brassinosteroid (BR), methyl jasmonate and abscisic acid (ABA) levels indicated that colour transitions are regulated by endogenous hormones. The DEGs involved in the auxin, cytokinin, gibberellin, BR, jasmonic acid and ABA signalling pathways were enriched and associated with petal colour transitions.ConclusionOur results provide global insight into the pigment accumulation and the regulatory mechanisms underlying petal colour transitions during the flower development process inL. japonica.

Background: Plants have remarkable diversity in petal color through the biosynthesis and accumulation of various pigments. To better understand the mechanisms regulating the petal pigmentation, we used multiple approaches to investigate the changes of carotenoids, gene expression dynamics and endogenous hormones in Lonicera japonica during petal color transitions, i.e. green bud petal (GB_Pe), white flower petal (WF_Pe) and yellow flower petal (YF_Pe). Results: Metabolome analysis showed that YF_Pe had a much higher content of carotenoids than white petals, with violaxanthin identified as the major carotenoid compound in YF_Pe. Comparative transcriptome analysis revealed that the key differentially expressed genes (DEGs) involved in carotenoid biosynthesis, such as phytoene synthase, phytoene desaturase and ζ-carotene desaturase, were significantly up-regulated in YF_Pe. However, expression levels of the carotenoid degradation-related genes, including abscisic-aldehyde oxidase 3 and carotenoid cleavage dioxygenase 4, were significantly down-regulated in YF_Pe. The results indicated that upregulated carotenoids concentrations and carotenoids biosynthesis-related genes promote the color transition. Furthermore, enrichment analysis of DEGs was mainly associated with the metabolic pathways of hormone signal transduction during petal color transitions. The DEGs were mainly involved in the auxin, cytokinin, gibberellin (GA), brassinosteroid (BR), jasmonic acid and abscisic acid (ABA) signal pathways. Accordingly, analyses of changes in indoleacetic acid, zeatin riboside, GA, BR, methyl jasmonate and ABA levels indicated that the color transitions are regulated by endogenous hormones. Conclusion: Our results provide new insight into the regulatory mechanisms underlying the petal color transitions during flower development process in L. japonica.