Plants exhibit remarkable diversity in their petal colors through biosynthesis and the accumulation of various pigments. Lilium, an important cut and potted flower, has many coloring pattern variations, including bicolors and spots. To elucidate the mechanisms regulating spot formation in Lilium leichtlinii var. maximowiczii petals, we used multiple approaches to investigate the changes in petal carotenoids, spot anthocyanins, and gene expression dynamics. This included green petals without spots (D1-Pe and D1-Sp), yellow–green petals with purple spots (D2-Pe and D2-Sp), light-orange petals with dark-purple spots (D3-Pe and D3-Sp), and orange petals with dark-purple spots (D4-Pe and D4-Sp). D3-Pe and D4-Pe contained large amounts of capsanthin and capsorubin and small amounts of zeaxanthin and violaxanthin, which contributed to the orange color. In addition to cyanidin-3-O-glucoside, pelargonidin-3-O-rutinoside, cyanidin-3-O-rutinoside, and peonidin-3-O-rutinoside may also contribute to L. leichtlinii var. maximowiczii‘s petal spot colors. KEGs involved in flavonoid biosyntheses, such as CHS, DFR, and MYB12, were significantly upregulated in D2-Sp and D3-Sp, compared with D1-Sp, as well as in spots, compared with petals. Upregulated anthocyanin concentrations and biosynthesis-related genes promoted spot formation and color transition. Our results provide global insight into pigment accumulation and the regulatory mechanisms underlying spot formation during flower development in L. leichtlinii var. maximowiczii.

The double-flowered lily ‘Red Twin’, in which stamens are transformed into petaloid organs, sometimes exhibits normal stamens owing to an unknown mechanism and thus greatly affecting its commercial quality. In this study, the morphogenesis of stamens and petaloid stamens in this cultivar grown under different temperature treatments were investigated. Two AGAMOUS-like genes were isolated and their expression levels were analyzed. The results showed that relatively high temperatures induced the morphogenesis of stamens, while relatively low temperatures promoted petaloidy in ‘Red Twin’. The stage with 1–6 mm flower buds was identified as the critical development period for stamen morphogenesis; furthermore, keeping the flower buds under relatively low temperatures in the 1–3 or 3–6 mm stages would be sufficient for the formation of petaloid stamens to a high degree. In addition, LrtAG1 and LrtAG2 showed the highest expression level in whorls 3 and 4 of 3–6 mm flower buds, respectively. LrtAG1 showed a higher reduction ratio than LrtAG2 when the flower buds were transferred to low temperature, implying that the decreased LrtAG1 expression level is associated with low temperature and might be correlated with the petaloidy of the stamens.