Transcriptome and Metabolome Combine to Analyze the Mechanism of Leaf Coloration Formation in Aeonium arboreum ‘Pink Sybil’

The decorative quality of succulents largely stems from their leaf color. Aeonium arboreum ‘Pink Sybil’ leaves feature an eye-catching stripe pattern which are particularly favored by customers, although the underlying mechanisms of its distinctive coloration are unknown. This study analyzed Aeonium arboreum ‘Pink Sybil’ leaves at the cellular and molecular levels. Freehand slices showed that anthocyanins were significantly distributed in the epidermal cells of RS (the red part of leaf margin), with limited accumulation in the GM (the green part of leaf center). UHPLC-HRMS revealed that cyanidin 3-galactoside was the main anthocyanin type responsible for the coloration of ‘Pink Sybil’ leaves, and its content accounted for 93.4% of the total flavonoid content in RS. The comparison of two transcripts identified 1817 DEGs, with 1123 upregulated and 694 downregulated genes. KEGG enrichment analysis revealed that the 20 most significantly enriched DEGs were involved in metabolic pathways, notably the phenylpropanoid and flavonoid biosynthesis pathways, which were closely related to the metabolism of anthocyanins. The majority of the structural genes and transcription factors involved in flavonoid metabolism were shown to be upregulated using qRT-PCR. Two transcription factors, AaNAC102 and AaNAC045, were preliminarily screened by gene co-expression network analysis, which promote the accumulation of anthocyanidins such as cyanidin 3,5-diglucoside and cyanidin 3-galactoside by positively regulating the expression of key structural genes such as CHS1, CHS2, UFGT1, UFGT2, and 4CL. Our findings clarified the major differential metabolites and differential genes in different leaf color parts of ‘Pink Sybil’ and provided a basis for further dissecting the biochemical processes behind brocade stripes leaf in Aeonium spp.