Post-transcriptional gene silencing of CYP76AD controls betalain biosynthesis in bracts of bougainvillea

Identification, expression analysis of quinoa betalain biosynthesis genes and their role in seed germination and cold stress

Betalains provide Chenopodium quinoa bright color, and the key enzyme genes for betalain biosynthesis include CYP76AD, DODA, and GTs. In this study, 59 CqCYP76AD, CqDODA and CqGTs genes in quinoa were identified and characterized by gene structural characteristics, phylogenetic relationships and gene expression patterns. The CqCYP76AD genes were divided into ɑ, β and γ types, CqDODA into ɑ and β types, and CqGTs into CqcDOPA5GT, CqB5GT and CqB6GT types according to phylogenetic relationships. The analysis of co-linearity identified eight pairs of duplicated genes which were subjected to purifying selection during evolution. CqCYP76AD and CqDODA, as well as CqcDOPA5GT and CqB5GT may have been evolutionarily linked in genetic inheritance, based on gene location and gene structure study. The tissue expression specificity of CqCYP76AD, CqDODA, and CqGTs genes in response to seed germination and cold stress was studied by RNA-Seq data. The genes CqCYP76AD, CqDODA, and CqGTs were involved in betalain biosynthesis and cold stress. CqCYP76AD, CqDODA, CqcDOPA5GT and CqB5GT gene sequences were consistent in the eight quinoa samples and showed significant variations in expression. In contrast, the inconsistency between changes in gene expression and betalain accumulation indicates that other factors may influence betalain biosynthesis in quinoa. This study offers the theoretical basis for the roles of the CqCYP76AD, CqDODA, and CqGTs genes in betalain biosynthesis and cold stress in quinoa, as well as a guide for the full utilization of betalains in quinoa plants.

Integrated metabolome, full-length sequencing, and transcriptome analyses unveil the molecular mechanisms of color formation of the canary yellow and red bracts of Bougainvillea × buttiana 'Chitra'

Bougainvillea is a typical tropical flower of great ornamental value due to its colorful bracts. The molecular mechanism behind color formation is not well-understood. Therefore, this research conducted metabolome analysis, transcriptome analysis, and multi-flux full-length sequencing in two color bracts of Bougainvillea × buttiana 'Chitra' to investigate the significantly different metabolites (SDMs) and differentially expressed genes (DEGs). Overall, 261 SDMs, including 62 flavonoids and 26 alkaloids, were detected, and flavonols and betalains were significantly differentially accumulated among the two bracts. Furthermore, the complete-length transcriptome of Bougainvillea × buttiana was also developed, which contained 512 493 non-redundant isoforms. Among them, 341 210 (66.58%) displayed multiple annotations in the KOG, GO, NR, KEGG, Pfam, Swissprot, and NT databases. RNA-seq findings revealed that 3610 DEGs were identified between two bracts. Co-expression analysis demonstrated that the DEGs and SDMs involved in flavonol metabolism (such as CHS, CHI, F3H, FLS, CYP75B1, kaempferol, and quercetin) and betacyanin metabolism (DODA, betanidin, and betacyanins) were the main contributors for the canary yellow and red bract formation, respectively. Further investigation revealed that several putative transcription factors (TFs) might interact with the promoters of the genes mentioned above. The expression profiles of the putative TFs displayed that they may positively and negatively regulate the structural genes' expression profiles. The data revealed a potential regulatory network between important genes, putative TFs, and metabolites in the flavonol and betacyanin biosynthesis of Bougainvillea × buttiana 'Chitra' bracts. These findings will serve as a rich genetic resource for future studies that could create new color bracts.

BpCYP76AD15 is involved in betaxanthin biosynthesis in bougainvillea callus

MAIN CONCLUSION

BpCYP76AD15 is involved in betaxanthin biosynthesis in callus, but not in bracts, in bougainvillea. Bougainvillea (Bougainvillea peruviana) is a climbing tropical ornamental tree belonging to Nyctaginaceae. Pigments that are conferring colorful bracts in bougainvillea are betalains, and that conferring yellow color are betaxanthins. In general, for red-to-purple betacyanin biosynthesis, α clade CYP76AD that has tyrosine hydroxylase and DOPA oxygenase activity is required, while for betaxanthin biosynthesis, β clade CYP76AD that has only tyrosine hydroxylase is required. To date, betaxanthin biosynthesis pathway genes have not been identified yet in bougainvillea. Since bougainvillea is phylogenetically close to four-O-clock (Mirabilis jalapa), and it was reported that β clade CYP76AD, MjCYP76AD15, is involved in floral betaxanthin biosynthesis in four-O-clock. Thus, we hypothesized that orthologous gene of MjCYP76AD15 in bougainvillea might be involved in bract betaxanthin biosynthesis. To test the hypothesis, we attempted to identify β clade CYP76AD gene from yellow bracts by RNA-seq; however, we could not. Instead, we found that callus accumulated betaxanthin and that β clade CYP76AD gene, BpCYP76AD15, were expressed in callus. We validated BpCYP76AD15 function by transgenic approach (agro-infiltration and over-expression in transgenic tobacco), and it was suggested that BpCYP76AD15 is involved in betaxanthin biosynthesis in callus, but not in bracts in bougainvillea. Interestingly, our data also indicate the existence of two pathways for betaxanthin biosynthesis (β clade CYP76AD-dependent and -independent), and the latter pathway is important for betaxanthin biosynthesis in bougainvillea bracts.

Transcriptome and Proteome Analysis Revealed the Influence of High-Molecular-Weight Glutenin Subunits (HMW-GSs) Deficiency on Expression of Storage Substances and the Potential Regulatory Mechanism of HMW-GSs

The processing quality of wheat is affected by seed storage substances, such as protein and starch. High-molecular-weight glutenin subunits (HMW-GSs) are the major components of wheat seed storage proteins (SSPs); they are also key determinators of wheat end-use quality. However, the effects of HMW-GSs absence on the expression of other storage substances and the regulation mechanism of HMW-GSs are still limited. Previously, a wheat transgenic line LH-11 with complete deletions of HMW-GSs was obtained through introducing an exogenous gene Glu-1E^bx to the wild-type cultivar Bobwhite by transgenic approach. In this study, comparative seed transcriptomics and proteomics of transgenic and non-transgenic lines at different seed developmental stages were carried out to explore the changes in genes and proteins and the underlying regulatory mechanism. Results revealed that a number of genes, including genes related to SSPs, carbohydrates metabolism, amino acids metabolism, transcription, translation, and protein process were differentially enriched. Seed storage proteins displayed differential expression patterns between the transgenic and non-transgenic line, a major rise in the expression levels of gliadins were observed at 21 and 28 days post anthesis (DPA) in the transgenic line. Changes in expressions of low-molecular-weight glutenins (LMW-GSs), avenin-like proteins (ALPs), lipid transfer proteins (LTPs), and protease inhibitors (PIs) were also observed. In addition, genes related to carbohydrate metabolism were differentially expressed, which probably leads to a difference in starch component and deposition. A list of gene categories participating in the accumulation of SSPs was proposed according to the transcriptome and proteome data. Six genes from the MYB and eight genes from the NAC transcription families are likely important regulators of HMW-GSs accumulation. This study will provide data support for understanding the regulatory network of wheat storage substances. The screened candidate genes can lay a foundation for further research on the regulation mechanism of HMW-GSs.

Pantranscriptome combined with phenotypic quantification reveals germplasm kinship and regulation network of bract color variation in Bougainvillea

Bracts are the metamorphic non-flower organ in angiosperm plants. The variation of the color and shape of bracts was found to be neo-functionalized (i.e., similar to petals), garnering research interest as a pollinator attractor. Bougainvillea is known for its specialized, large, and colorful bracts, which contrast with its tiny colorless flowers. As a plant whose bracts vary greatly in terms of coloration, the molecular mechanisms for Bougainvillea bract coloration and polychroism are largely unknown. The lack of genomic information for Bougainvillea largely hinders studies into the evolution and genetic basis of bract color variation. In this study, a pan-transcriptome of bracts obtained from 18 Bougainvillea glabra accessions was employed to investigate the global population-level germplasm kinship and the gene regulation network for bract color variation. Our results showed that the bracts of B. glabra accessions have largely differentiated International Commission on Illumination (CIE) L-a-b values. Moreover, germplasm kinship detected using principal component analysis, phylogeny, and admixture analysis showed three optimal subgroups, two of them distinctly clustered, which were not directly correlated with bract color variation at the population level. Differentially expressed genes (DEGs) between accessions of high vs. low L-a-b values revealed several considerable upregulated genes related to bract color L-a-b variation. A weighted gene co-expression network was constructed, and eight co-expressed regulation modules were identified that were highly correlated with variation in bract CIE L-a-b color values. Several candidate DEGs and co-expressed hub genes (e.g., GERD, SGR, ABCA3, GST, CYP76AD1, CYP76C, and JAZ) that were tightly associated with bract color variation were eventually determined responsible for L-a-b colorations, which might be the core regulation factors contributing to the B. glabra bract color variation. This study provides valuable insights into the research on germplasm kinship, population-level pan-transcriptome expression profiles, and the molecular basis of color variation of key innovative bracts in horticultural Bougainvillea.