American lotus (Nelumbo lutea) is one of the two species in Nelumbo and has only yellow flower. Identification of total flavonoids showed wild American lotus contained almost only flavonols with quercetin 3-O-glucuronide to be the dominant pigment. The variation tendency of the total flavonol content was coincident with yellow color variation of petals during flower development. To understand the mechanism of accumulation and constituent of pigments in petals, three pivotal genes, NlFLS1, NlFLS2 and NlFLS3, which were predicted to encode flavonol synthases were isolated and characterized by analyses of basic bioinformatics, temporal and spatial expression patterns and enzymatic activity. Their temporal expression levels showed the same variation tendency, which was also consistent with the development-dependent variation of total flavonol content. Spatial expression patterns indicated the three genes should function in petals. All the three proteins were demonstrated to be bifunctional dioxygenase, possessing both flavonol synthase activity and flavanone 3-hydroxylase activity. Besides, other flavonol biosynthesis related genes were also investigated on their expression levels to give more clues on the mechanism. Substrate preferences of the three FLSs, substrate competitions between the FLSs and other flavonol biosynthesis related enzymes, and the greatly differential expression levels between F3'H (flavonoid 3′-hydroxylase) and F3'5'H (flavonoid 3′,5′-hydroxylase) contributed to the flavonol constituent in the petals of America lotus, namely abundant quercetin-derivatives while very few kaempferol-derivatives and myricetin-derivatives.

Previous studies have shown that high light intensity can induce anthocyanin synthesis (AS) in petunia plants. To identify which kind of light quality plays a role in inducing such metabolic process, and what transcripts participate in controlling it, we carried out whole-transcriptome sequencing and analysis of petunia petals treated with different light-quality conditions. Among the red and white light treatments, a total of 2 205 differentially expressed genes and 15, 22, and 20 differentially expressed circRNAs, miRNAs, and lncRNAs, were identified respectively. The AS-related genes, including the structural genes CHSj, F3′H, F3′5′H, DFR, and ANS, and the regulatory genes AN4, DPL, PHZ and MYBx were found to be downregulated under red light condition compared with their levels under white light condition. Furthermore, the light photoreceptor Cryptochrome 3 (CRY3) and a series of light-dependent genes, such as PIF, HY5, and BBXs, were also determined to respond to the light treatments. The anthocyanin contents in early petunia petals under red light were significantly lower than that under white and blue light. The results of qRT-PCR further confirmed the expression pattern of some AS-related and light-response genes in response to different light quality. Yeast two-hybrid results showed that the key elements in the light signal pathway, HY5 can interact with BBX19, BBX24 and BBX25. And PHZ, the important AS regulator can induce anthocyanin synthesis in response to blue light quality from transient expression analysis in petunia petals. These findings presented here not only deepen our understanding of how light quality controls anthocyanin synthesis, but also allow us to explore potential target genes for improving pigment production in petunia flower petals.

Paeonia species are important ornamental plants, including three types: tree peony, herbaceous peony, and Itoh hybrid peony. Paeonia with yellow color is desired and becoming popular. However, the chemical mechanism of the formation of yellow flowers in Paeonia is still unclear. In this study, 14 representative samples were selected: four samples of three species of Paeonia, four herbaceous peony cultivars, three lutea hybrid tree peony cultivars, and three Itoh hybrid peony cultivars. The petal extracts of the samples were determined by HPLC-DAD and HPLC-Q-TOF-MS/MS. In total, 29 flavonoids were isolated and identified, including 28 flavonol glycosides and one chalcone derivative. There were significant differences in the composition and content of flavonoids in petals of different cultivars (species). The total content of flavonoids was between 19.430 and 143.043 mg • g⁻¹ DW. Flavonol glycosides were detected in all samples. Chalconaringenin 2′-O-glucoside was detected from one herbaceous peony cultivar ‘Golden Wheel’ lutea hybrid tree peony cultivars, and Itoh peony cultivars. The content of chalconaringenin 2′-O-glucoside in the samples was more than 43% of total flavonoids. The pigment type and content of lutea hybrid tree peonies and Itoh hybrid peonies are similar. Total flavonoids, especially quercetin 3-O-galloylglucoside and chalconaringenin 2′-O-glucoside contribute greatly to the formation of yellow flowers of Paeonia. The results of this study provide a comprehensive understanding of the chemical mechanism for yellow flower coloration of Paeonia, and lay the foundation for yellow flower breeding of Paeonia.