Leaf color formation mechanisms in Alternanthera bettzickiana elucidated by metabolite and transcriptome analyses

The difference in leaf color among the three cultivars of A. bettzickiana is due to different chloroplast morphology and chlorophyll-to-anthocyanin ratios. Alternanthera bettzickiana is one of the most important ornamental plants in modern flower beds because of its colorful leaves. The present study examined the mechanism of leaf color formation in A. bettzickiana. Three cultivars of A. bettzickiana (red, green, and mixed red and green) were selected for comprehensive analyses of leaf color formation by examining cellular and subcellular structures and pigment biosynthesis and metabolism. The difference in leaf colors between the three cultivars of A. bettzickiana was due to different chlorophyll-to-anthocyanin ratios. A. bettzickiana 'Green' showed very low expression of CHS, F3H, and DFR, the key genes of the anthocyanin biosynthesis pathway, and a low anthocyanin content but had mature chloroplasts and a green color. A. bettzickiana 'Red' exhibited a low chlorophyll content and deformed chloroplasts but a high cyanidin content and, thus, a red color. A. bettzickiana 'Variegated' presented high anthocyanin and chlorophyll contents and exhibited red and green variegation, indicating a balance between coloration and photosynthetic efficiency. These data provide a good explanation for the coloration of different cultivars of A. bettzickiana and an important reference for better explaining the color formation mechanisms of plant leaves.