Integrative metabolome and transcriptome analysis reveal the molecular mechanism of yellow-red bicolor formation in Kalanchoe blossfeldiana petals

The winter pot kalanchoe (Kalanchoe blossfeldiana) is an ornamental plant with succulent leaves and clustered flowers in Crassulaceae, widely used as potted flower or garden decoration. Although diverse cultivars with vivid petal colors are bred out and easily obtained in the market, the potential molecular mechanism of pigmentation is poorly understood. This study collected a yellow-red colored winter pot kalanchoe to investigate its molecular mechanism underlying bicolor formation. The metabolome results showed that both flavonoid and carotenoid were co-existing in the winter pot kalanchoe petals, whereas only anthocyanin accumulation showed significant differences, about nineteen times higher in the red region than that in the yellow region. The differentially expressed genes were significantly enriched in the anthocyanin biosynthesis pathway, and the expression level of biosynthetic genes including KbCHS, KbCHI, KbF3H, KbDFR, KbANS and KbGTs were significantly upregulated in the red region. Moreover, transcription factors potentially involved in regulating anthocyanin biosynthesis was predicted, and KbMYB2 and KbbHLH1 might play important roles in positively regulating anthocyanin biosynthesis in the red region. The findings reported here provide new insights into the understanding of petal bicolor formation mechanism, and will assist cultivar innovation in winter pot kalanchoe.