Integrated metabolic profiling and transcriptome analysis of pigment accumulation in Lonicera japonica flower petals during colour-transition

Abstract

Background: Plants 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).

Results: Metabolome 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.

Conclusion: Our results provide global insight into the pigment accumulation and the regulatory mechanisms underlying petal colour transitions during the flower development process in L. japonica.

Keywords: Endogenous hormones; Gene expression; Lonicera japonica; Petal colour; Pigment.

Fig. 1

Morphological observation of L. japonica flowers. a Flower buds with green petals (GB_Pe). b Flowers with white petals (WF_Pe). c Flowers with yellow petals (YF_Pe)

Fig. 2

Concentrations of endogenous hormones in petal color transitions in L. japonica. a IAA concentration. b ZR concentration. c GA₃ concentration. d BR concentration. e MeJA concentration. f ABA concentration. Significant differences are indicated by different letters at P < 0.05

Fig. 3

Analysis of DEGs. a Cluster analysis of all DEGs from the expression profiles. Black lines indicated the average expression level of unigenes grouped into the same profile. b Enrichment of selected GO terms for DEGs (> 1 RPKM) selected from profiles 3 and 4. The biological process with false discovery rate (adjusted P < 0.05, Student’s t-test) is shown

Fig. 4

Expression levels of the pigments synthesis/catabolism in GB_Pe, WF_Pe and YF_Pe. a DEGs of carotenoid metabolism-related genes. b DEGs of porphyrin and chlorophyll metabolism-related genes. c DEGs of flavonoid/anthocyanin metabolism-related genes. High expression levels are represented in orchid. Low expression levels are represented in blue

Fig. 5

Validation of the expression of pigment-related genes in L. japonica by RT-qPCR. Error bars indicate the standard deviation of three independent biological repeats. Significant differences are indicated by different letters at P < 0.05

Fig. 6

Schematic of changes in the regulatory genes and metabolites in petal color- transition in L. japonica