Flavonoid Synthesis-Related Genes Determine the Color of Flower Petals in Brassica napus L

An integrated QTL and RNA-seq analysis revealed new petal morphology loci in Brassica napus L

BACKGROUND

Rapeseed (Brassica napus L.) is one of the most important oil crops and a wildly cultivated horticultural crop. The petals of B. napus serve to protect the reproductive organs and attract pollinators and tourists. Understanding the genetic basis of petal morphology regulation is necessary for B. napus breeding.

RESULTS

In the present study, the quantitative trait locus (QTL) analysis for six B. napus petal morphology parameters in a double haploid (DH) population was conducted across six microenvironments. A total of 243 QTLs and five QTL hotspots were observed, including 232 novel QTLs and three novel QTL hotspots. The spatiotemporal transcriptomic analysis of the diversiform petals was also conducted, which indicated that the expression of plant hormone metabolic and cytoskeletal binding protein genes was variant among diversiform petals.

CONCLUSIONS

The integration of QTL and RNA-seq analysis revealed that plant hormones (including cytokinin, auxin, and gibberellin) and cytoskeleton were key regulators of the petal morphology. Subsequently, 61 high-confidence candidate genes of petal morphology regulation were identified, including Bn.SAUR10, Bn.ARF18, Bn.KIR1, Bn.NGA2, Bn.PRF1, and Bn.VLN4. The current study provided novel QTLs and candidate genes for further breeding B. napus varieties with diversiform petals.

Unraveling the mechanism of flower color variation in Brassica napus by integrated metabolome and transcriptome analyses

Brassica napus is one of the most important oil crops in the world. Breeding oilseed rape with colorful flowers can greatly enhance the ornamental value of B. napus and thus improve the economic benefits of planting. As water-soluble flavonoid secondary metabolites, anthocyanins are very important for the synthesis and accumulation of pigments in the petals of plants, giving them a wide range of bright colors. Despite the documentation of over 60 distinct flower shades in B. napus, the intricacies underlying flower color variation remain elusive. Particularly, the mechanisms driving color development across varying flower color backgrounds necessitate further comprehensive investigation. This research undertook a comprehensive exploration through the integration of transcriptome and metabolome analyses to pinpoint pivotal genes and metabolites underpinning an array of flower colors, including beige, beige-red, yellow, orange-red, deep orange-red, white, light-purple, and purple. First, we used a two-way BLAST search to find 275 genes in the reference genome of B. napus Darmor v10 that were involved in making anthocyanins. The subsequent scrutiny of RNA-seq outcomes underscored notable upregulation in the structural genes F3H and UGT, alongside the MYB75, GL3, and TTG1 transcriptional regulators within petals, showing anthocyanin accumulation. By synergizing this data with a weighted gene co-expression network analysis, we identified CHS, F3H, MYB75, MYB12, and MYB111 as the key players driving anthocyanin synthesis in beige-red, orange-red, deep orange-red, light-purple, and purple petals. By integrating transcriptome and weighted gene co-expression network analysis findings with anthocyanin metabolism data, it is hypothesized that the upregulation of MYB75, which, in turn, enhances F3H expression, plays a pivotal role in the development of pigmented oilseed rape flowers. These findings help to understand the transcriptional regulation of anthocyanin biosynthesis in B. napus and provide valuable genetic resources for breeding B. napus varieties with novel flower colors.

The formation and evolution of flower coloration in Brassica crops

The flower coloration of Brassica crops possesses significant application and economic value, making it a research hotspot in the field of genetics and breeding. In recent years, great progress has been made in the research on color variation and creation of Brassica crops. However, the underlying molecular mechanisms and evolutional processes of flower colors are poorly understood. In this paper, we present a comprehensive overview of the mechanism of flower color formation in plants, emphasizing the molecular basis and regulation mechanism of flavonoids and carotenoids. By summarizing the recent advances on the genetic mechanism of flower color formation and regulation in Brassica crops, it is clearly found that carotenoids and anthocyanins are major pigments for flower color diversity of Brassica crops. Meantime, we also explore the relationship between the emergence of white flowers and the genetic evolution of Brassica chromosomes, and analyze the innovation and multiple utilization of Brassica crops with colorful flowers. This review aims to provide theoretical support for genetic improvements in flower color, enhancing the economic value and aesthetic appeal of Brassica crops.

Multi-Omics Analysis Reveals That Anthocyanin Degradation and Phytohormone Changes Regulate Red Color Fading in Rapeseed (Brassica napus L.) Petals

Flower color is an important trait for the ornamental value of colored rapeseed (Brassica napus L.), as the plant is becoming more popular. However, the color fading of red petals of rapeseed is a problem for its utilization. Unfortunately, the mechanism for the process of color fading in rapeseed is unknown. In the current study, a red flower line, Zhehuhong, was used as plant material to analyze the alterations in its morphological and physiological characteristics, including pigment and phytohormone content, 2 d before flowering (T1), at flowering (T2), and 2 d after flowering (T3). Further, metabolomics and transcriptomics analyses were also performed to reveal the molecular regulation of petal fading. The results show that epidermal cells changed from spherical and tightly arranged to totally collapsed from T1 to T3, according to both paraffin section and scanning electron microscope observation. The pH value and all pigment content except flavonoids decreased significantly during petal fading. The anthocyanin content was reduced by 60.3% at T3 compared to T1. The content of three phytohormones, 1-aminocyclopropanecarboxylic acid, melatonin, and salicylic acid, increased significantly by 2.2, 1.1, and 30.3 times, respectively, from T1 to T3. However, auxin, abscisic acid, and jasmonic acid content decreased from T1 to T3. The result of metabolomics analysis shows that the content of six detected anthocyanin components (cyanidin, peonidin, pelargonidin, delphinidin, petunidin, and malvidin) and their derivatives mainly exhibited a decreasing trend, which was in accordance with the trend of decreasing anthocyanin. Transcriptomics analysis showed downregulation of genes involved in flavonol, flavonoid, and anthocyanin biosynthesis. Furthermore, genes regulating anthocyanin biosynthesis were preferentially expressed at early stages, indicating that the degradation of anthocyanin is the main issue during color fading. The corresponding gene-encoding phytohormone biosynthesis and signaling, JASMONATE-ZIM-DOMAIN PROTEIN, was deactivated to repress anthocyanin biosynthesis, resulting in fading petal color. The results clearly suggest that anthocyanin degradation and phytohormone regulation play essential roles in petal color fading in rapeseed, which is a useful insight for the breeding of colored rapeseed.

Multi-Omics Analysis Revealed the AGR-FC.C3 Locus of Brassica napus as a Novel Candidate for Controlling Petal Color

Variations in the petal color of Brassica napus are crucial for ornamental value, but the controlled loci for breeding remain to be unraveled. Here, we report a candidate locus, AGR-FC.C3, having conducted a bulked segregant analysis on a segregating population with different petal colors. Our results showed that the locus covers 9.46 Mb of the genome, harboring 951 genes. BnaC03.MYB4, BnaC03.MYB85, BnaC03.MYB73, BnaC03.MYB98, and BnaC03.MYB102 belonging to MYB TFs families that might regulate the petal color were observed. Next, a bulk RNA sequencing of white and orange-yellow petals on three development stages was performed to further identify the possible governed genes. The results revealed a total of 51 genes by overlapping the transcriptome data and the bulked segregant analysis data, and it was found that the expression of BnaC03.CCD4 was significantly up-regulated in the white petals at three development stages. Then, several novel candidate genes such as BnaC03.ENDO3, BnaC03.T22F8.180, BnaC03.F15C21.8, BnaC03.Q8GSI6, BnaC03.LSD1, BnaC03.MAP1Da, BnaC03.MAP1Db, and BnaC03G0739700ZS putative to controlling the petal color were identified through deeper analysis. Furthermo re, we have developed two molecular markers for the reported functional gene BnaC03.CCD4 to discriminate the white and orange-yellow petal colors. Our results provided a novel locus for breeding rapeseed with multi-color petals.

An LcMYB111-LcHY5 Module Differentially Activates an LcFLS Promoter in Different Litchi Cultivars

Flavonol synthase (FLS) is the crucial enzyme of the flavonol biosynthetic pathways, and its expression is tightly regulated in plants. In our previous study, two alleles of LcFLS,LcFLS-A and LcFLS-B, have been identified in litchi, with extremely early-maturing (EEM) cultivars only harboring LcFLS-A, while middle-to-late-maturing (MLM) cultivars only harbor LcFLS-B. Here, we overexpressed both LcFLS alleles in tobacco, and transgenic tobacco produced lighter-pink flowers and showed increased flavonol levels while it decreased anthocyanin levels compared to WT. Two allelic promoters of LcFLS were identified, with EEM cultivars only harboring proLcFLS-A, while MLM cultivars only harbor proLcFLS-B. One positive and three negative R2R3-MYB transcription regulators of LcFLS expression were identified, among which only positive regulator LcMYB111 showed a consistent expression pattern with LcFLS, which both have higher expression in EEM than that of MLM cultivars. LcMYB111 were further confirmed to specifically activate proLcFLS-A with MYB-binding element (MBE) while being unable to activate proLcFLS-B with mutated MBE (MBEm). LcHY5 were also identified and can interact with LcMYB111 to promote LcFLS expression. Our study elucidates the function of LcFLS and its differential regulation in different litchi cultivars for the first time.

Metabolomics Analysis Reveals the Accumulation Patterns of Flavonoids and Volatile Compounds in Camellia oleifera Petals with Different Color

To systematically and comprehensively investigate the metabolic characteristics of coloring substances and floral aroma substances in Camellia oleifera petals with different colors, ultrahigh-performance liquid chromatography-mass spectrometry (UPLC-MS/MS) and headspace solid phase microextraction and gas chromatography-mass spectrometry (HS-SPME-GC-MS) metabolomics methods were applied to determine the metabolic profiles of white, candy-pink and dark-red petals. The results revealed that 270 volatile organic compounds were detected, mainly terpenoids, heterocyclic, esters, hydrocarbons, aldehydes, and alcohols, in which phenylethyl alcohol, lilac alcohol, and butanoic acid, 1-methylhexyl ester, hotrienol, alpha-terpineol and 7-Octen-4-ol, 2-methyl-6-methylene-, (S)-, butanoic acid, 2-methyl-, 2-methylbutyl ester, 2,4-Octadienal, (E,E)- could act as the floral scent compounds. A total of 372 flavonoid compounds were identified, and luteolin, kaempferol, cyanidin and peonidin derivatives were considered as the main coloring substances for candy-pink and dark-red petal coloration. In conclusion, this study intuitively and quantitatively exhibited the variations in flower color and floral scent of C. oleifera petal with different colors caused by changes in variations of flavonoids and volatile organic compound composition, and provided useful data for improving the sensory quality and breeding of C. oleifera petals.

Characterization Variation of the Differential Coloring Substances in Rapeseed Petals with Different Colors Using UPLC-HESI-MS/MS

Rapeseed's (Brassica napus L.) colorful petals have important ornamental values. However, the mechanisms of regulating petals coloration in rapeseed are still unknown. In our study, we investigated the key differential coloring substances in nine rapeseed cultivars with different petal colors, and 543 metabolites were detected and characterized through UPLC-HESI-MS/MS. Among them, the kinds and contents of flavonols, flavones, and anthocyanidins were the main contributors to petals' coloration. Tamarixetin-, quercetin-, butin-, naringenin- and luteolin-derivates were the main pigment bases in white and yellow petals. Peonidin-3,5-O-diglucoside, peonidin-3-O-(6″-O-caffeoyl)glucoside, and quercetin-derivatives were the main coloring substances in pink petals. Acylated cyanidin derivatives might lead to a series of different purple petal colors. Glycosylated anthocyanins were responsible for the coloration of rapeseed red petals, and peonidin-3-O-glucoside and kaempferol-derivatives were mainly detected from the red petals. These results provide comprehensive insights into the difference in flavonoid metabolites in rapeseed petals with different colors and supply theoretical supports for the breeding of novel colorful rapeseed cultivars.

Transcriptomic and Metabolomic Analyses Reveal Differences in Flavonoid Pathway Gene Expression Profiles between Two Dendrobium Varieties during Vernalization

Dendrobium (Orchidaceae, Epidendoideae) plants have flowers with a wide variety of colors that persist for a long period throughout the year. The yellow coloration of Dendrobium flowers is mainly determined by the flavonol pathway and the flavone pathway, but the relevant biosynthesis mechanisms during vernalization remain unclear. To explore the similarities and differences in flavonoid biosynthesis in different tissues during vernalization, we selected two species of Dendrobium for a flower color study: Dendrobium capillipes Rchb (which has yellow flowers) and Dendrobium nobile Lindl (which has white flowers). We collected a total of 36 samples from six tissue types and both Dendrobium species during vernalization and subjected the samples to metabolic profiling and transcriptome sequencing. A total of 31,504 differentially expressed genes (DEGs) were identified between different tissues of the two Dendrobium species by transcriptomic analysis. However, many differentially accumulated metabolites (DAMs) and DEGs were enriched not only in the general pathway of "flavonoid biosynthesis" but also in multiple subpathways of "flavone and flavonol biosynthesis". According to a combined transcriptome and metabolome analysis, Putrescine hydroxycinnamoyl transferase 1 (LOC110093422) may be the main gene responsible for the differences in flavonoid accumulation during vernalization, which is closely associated with yellow flowers. Taken together, the results of our study preliminarily revealed the metabolites responsible for and the key genes regulating flavonoid biosynthesis during vernalization. These results provide a basis for the further study of the molecular mechanism of flavonoid synthesis during vernalization.