Abstract
BackgroundPlants have remarkable diversity in petal colour through the biosynthesis and accumulation of various pigments. To better understand the mechanisms regulating petal pigmentation in Lonicera 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 as phytoene synthase, phytoene desaturase and ζ-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 an anthocyanidin synthase gene 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 in L. japonica.
Highlights
Plants have remarkable diversity in petal colour through the biosynthesis and accumulation of various pigments
With this extensive analysis of multiple data points in L. japonica petals, we reveal changes in the key pigments, hormones, and related biosynthesis genes that are associated with petal colour transitions
Analyses of key candidate genes, metabolites and hormones highlighted the effects of carotenoids, anthocyanins and endogenous hormones; this enabled us to clarify the regulatory mechanisms underlying the transitions
Summary
Plants have remarkable diversity in petal colour through the biosynthesis and accumulation of various pigments. Different plant lineages have adopted various mechanisms of flower colour determination to fulfil the requirements for pollinator attraction or non-pollinatorrelated traits [1]. Three major classes of pigments, flavonoids/anthocyanins, carotenoids and chlorophylls, are distributed ubiquitously in plants. Among them, pigmented flavonoids, mainly anthocyanins, are major pigmentation compounds in flowering plants [5]. Carotenoids widely participate in the yellow-to-red colouration of flowers [7]. Chlorophylls, which are a class of essential photosynthetic components, exist in almost all plants and are mainly involved in the formation of green colour in flowers [8]. Anthocyanins and carotenoids often coexist simultaneously, and their combination causes diversity in flower colour [9]
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