Ectopic expression of tea MYB genes alter spatial flavonoid accumulation in alfalfa (Medicago sativa)

Integrated Analyses of the Mechanism of Flower Color Formation in Alfalfa (Medicago sativa)

BACKGROUND

Alfalfa (Medicago sativa) is one of the most valuable forages in the world. As an outcrossing species, it needs bright flowers to attract pollinators to deal with self-incompatibility. Although various flower colors have been observed and described in alfalfa a long time ago, the biochemical and molecular mechanism of its color formation is still unclear.

METHODS

By analyzing alfalfa lines with five contrasting flower colors including white (cream-colored), yellow, lavender (purple), dark purple and dark blue, various kinds and levels of anthocyanins, carotenoids and other flavonoids were detected in different colored petals, and their roles in color formation were revealed.

RESULTS

Notably, the content of delphinidin-3,5-O-diglucoside in lines 3, 4 and 5 was 58.88, 100.80 and 94.07 times that of line 1, respectively. Delphinidin-3,5-O-diglucoside was the key factor for purple and blue color formation. Lutein and β-carotene were the main factors for the yellow color formation. By analyzing differentially expressed genes responsible for specific biochemical pathways and compounds, 27 genes were found to be associated with purple and blue color formation, and 14 genes were found to play an important role in yellow color formation.

CONCLUSIONS

The difference in petal color between white, purple and blue petals was mainly caused by the accumulation of delphinidin-3,5-O-diglucoside. The difference in petal color between white and yellow petals was mainly affected by the production of lutein and β-carotene. These findings provide a basis for understanding the biochemical and molecular mechanism of alfalfa flower color formation.

CsRAB, a R2R3-MYB transcription factor from purple tea (Camellia sinensis), positively regulates anthocyanin biosynthesis

In tea (Camellia sinensis), anthocyanins are important secondary metabolites that are linked to leaf color. Anthocyanin biosynthesis is a complex biological process, in which multiple genes including structural and regulatory genes are involved. Here, we describe the cloning and characterizing of a new R2R3-MYB transcription factor gene, CsRAB, isolated from purple tea variety 'Hongfei'. Consistent with its predicted role as a transcription factor, the CsRAB protein localized to nuclei when expressed in onion (Allium cepa) epidermal cell. A dual-luciferase reporter assay demonstrated that CsRAB acts as a transcriptional activator in vivo. CsRAB overexpression in Arabidopsis seedlings led to higher expression levels of anthocyanin biosynthesis-related genes, and consequently, purple stems and higher anthocyanin contents were exhibited in overexpressing lines compared to wild type. The results indicated that CsRAB plays critical roles in positively regulating anthocyanins biosynthesis in tea plants.

CsPHRs-CsJAZ3 incorporates phosphate signaling and jasmonate pathway to regulate catechin biosynthesis in Camellia sinensis

Catechins constitute abundant metabolites in tea and have potential health benefits and high economic value. Intensive study has shown that the biosynthesis of tea catechins is regulated by environmental factors and hormonal signals. However, little is known about the coordination of phosphate (Pi) signaling and the jasmonic acid (JA) pathway on biosynthesis of tea catechins. We found that Pi deficiency caused changes in the content of catechins and modulated the expression levels of genes involved in catechin biosynthesis. Herein, we identified two transcription factors of phosphate signaling in tea, named CsPHR1 and CsPHR2, respectively. Both regulated catechin biosynthesis by activating the transcription of CsANR1 and CsMYB5c. We further demonstrated CsSPX1, a Pi pathway repressor, suppressing the activation by CsPHR1/2 of CsANR1 and CsMYB5c. JA, one of the endogenous plant hormones, has been reported to be involved in the regulation of secondary metabolism. Our work demonstrated that the JA signaling repressor CsJAZ3 negatively regulated catechin biosynthesis via physical interaction with CsPHR1 and CsPHR2. Thus, the CsPHRs-CsJAZ3 module bridges the nutrition and hormone signals, contributing to targeted cultivation of high-quality tea cultivars with high fertilizer efficiency.

Effect of dietary inclusion of tea residue and tea leaves on ruminal fermentation characteristics and methane production

The aim of this study was to compare the differences of dietary tea leaves (TL) and tea residue (TR) inclusion on rumen fermentation characteristics and to explore whether TR could be an alternative feedstuff of ruminants. For these purposes, seven treatments consisted of two inclusion types (TL vs. TR) and three inclusion levels (g/g of dry matter basis) of 10% (TL10/TR10), 20% (TL20/TR20), and 30% (TL30/TR30) in each inclusion type, plus control group with inclusion of 0% (CON) were designed, with four replicates in each group, to conduct an in vitro ruminal fermentation test. Results showed that the contents of crude protein, neutral detergent fiber, and acid detergent fiber were higher in TR than TL, while TL contained more ether extract and crude ash than TR. Interaction effects between inclusion type and inclusion level were observed in concentrations of isobutyrate and microbial crude protein (MCP), as well as in gas production and digestibility of organic matter. Fermentation characteristics were significantly influenced by TL and TR depending on the inclusion level, except for the concentration of total branched-chain volatile fatty acid. These significant differences of fermentation characteristics due to inclusion level mainly focused on CON and tea inclusion, with higher values in CON than TR or TL groups. The total gas production during the 48-h incubation showed no differences among CON, TL10, and TR10. The inclusion of TR and TL decreased the production of methane. The concentration of MCP in CON, TR10 and TR30 was lower than TR20 and all TL groups. In conclusion, dietary inclusion of TR and TL possessed equivalent effect on rumen fermentation characteristics and methane production, substituting diet with TR or TL for over 10% would inhibit rumen fermentation despite positive effects in TR20 and all TL groups regarding more MCP and less methane production. This study indicates that special attention should be paid to the inclusion level of TR and TL when considering them as alternative feedstuffs of ruminants. Further in vivo study is needed to evaluate the applicability of tea residue as a feedstuff for production of ruminants.

Anthocyanin metabolism and its differential regulation in purple tea (Camellia sinensis)

Tea plants (Camellia sinensis) typically contain high-flavonoid phytochemicals like catechins. Recently, new tea cultivars with unique purple-colored leaves have gained attention. These purple tea cultivars are enriched with anthocyanin, which provides an interesting perspective for studying the metabolic flux of the flavonoid pathway. An increasing number of studies are focusing on the leaf color formation of purple tea and this review aims to summarize the latest progress made on the composition and accumulation of anthocyanins in tea plants. In addition, the regulation mechanism in its synthesis will be discussed and a hypothetical regulation model for leaf color transformation during growth will be proposed. Some novel insights are presented to facilitate future in-depth studies of purple tea to provide a theoretical basis for targeted breeding programs in leaf color.

Transcriptome and metabolome analyses reveal molecular mechanisms of anthocyanin-related leaf color variation in poplar (Populus deltoides) cultivars

INTRODUCTION

Colored-leaf plants are increasingly popular for their aesthetic, ecological, and social value, which are important materials for research on the regulation of plant pigments. However, anthocyanin components and the molecular mechanisms of anthocyanin biosynthesis in colored-leaf poplar remain unclear. Consequently, an integrative analysis of transcriptome and metabolome is performed to identify the key metabolic pathways and key genes, which could contribute to the molecular mechanism of anthocyanin biosynthesis in the colored-leaf cultivars poplar.

METHODS

In this study, integrated metabolite and transcriptome analysis was performed to explore the anthocyanin composition and the specific regulatory network of anthocyanin biosynthesis in the purple leaves of the cultivars 'Quanhong' (QHP) and 'Zhongshanyuan' (ZSY). Correlation analysis between RNA-seq data and metabolite profiles were also performed to explore the candidate genes associated with anthocyanin biosynthesis. R2R3-MYB and bHLH TFs with differential expression levels were used to perform a correlation analysis with differentially accumulated anthocyanins.

RESULTS AND DISCUSSION

A total of 39 anthocyanin compounds were detected by LC-MS/MS analysis. Twelve cyanidins, seven pelargonidins, five delphinidins, and five procyanidins were identified as the major anthocyanin compounds, which were differentially accumulated in purple leaves of QHP and ZSY. The major genes associated with anthocyanin biosynthesis, including structural genes and transcription factors, were differentially expressed in purple leaves of QHP and ZSY through RNA-sequencing (RNA-seq) data analysis, which was consistent with quantitative real-time PCR analysis results. Correlation analysis between RNA-seq data and metabolite profiles showed that the expression patterns of certain differentially expressed genes in the anthocyanin biosynthesis pathway were strongly correlated with the differential accumulation of anthocyanins. One R2R3-MYB subfamily member in the SG5 subgroup, Podel.04G021100, showed a similar expression pattern to some structural genes. This gene was strongly correlated with 16 anthocyanin compounds, indicating that Podel.04G021100 might be involved in the regulation of anthocyanin biosynthesis. These results contribute to a systematic and comprehensive understanding of anthocyanin accumulation and to the molecular mechanisms of anthocyanin biosynthesis in QHP and ZSY.

R2R3-MYB gene family: Genome-wide identification provides insight to improve the content of proanthocyanidins in Trifolium repens

The R2R3-MYB family is one of largest transcription factor families in plants playing significant roles in regulating anthocyanin and proanthocyanidin biosynthesis. Proanthocyanidins are one of major objectives to improve the quality of white clover (Trifolium repens L.), which have a beneficial effect on ruminant to prevent the lethal pasture bloat. A total of 133 TrR2R3-MYB genes were identified and distributed on all 16 chromosomes based on the whole genome information of white clover. Also, by exploring the gene structure, motifs and duplication events of TrR2R3-MYBs, as well as the evolutionary relationship with TrR2R3-MYB genes of other species, 10 TrR2R3-MYB genes with the potential to regulate the anthocyanins and proanthocyanidins biosynthesis were screened. These TrR2R3-MYB genes responded significantly to low temperature in white clover. In addition, they have different expression patterns in leaves, petioles and inflorescences of white clover. Importantly, TrMYB116 and TrMYB118 may positively regulate anthocyanin accumulation and low temperature response in white clover. TrMYB118 may also be associated with anthocyanin pigmentation pattern in Purple leaves. This study provides a basis for verifying the function of TrR2R3-MYB and breeding white clover cultivars with high proanthocyanidins.

Reverse genetic approaches for breeding nutrient-rich and climate-resilient cereal and food legume crops

In the last decade, advancements in genomics tools and techniques have led to the discovery of many genes. Most of these genes still need to be characterized for their associated function and therefore, such genes remain underutilized for breeding the next generation of improved crop varieties. The recent developments in different reverse genetic approaches have made it possible to identify the function of genes controlling nutritional, biochemical, and metabolic traits imparting drought, heat, cold, salinity tolerance as well as diseases and insect-pests. This article focuses on reviewing the current status and prospects of using reverse genetic approaches to breed nutrient-rich and climate resilient cereal and food legume crops.

Regulation of biosynthesis of the main flavor-contributing metabolites in tea plant (Camellia sinensis): A review

In the process of adapting to the environment, tea plants (Camellia sinensis) endow tea with unique flavor and health functions, which should be attributed to secondary metabolites, including catechins, L-theanine, caffeine and terpene volatiles. Since the content of these flavor-contributing metabolites are mainly determined by the growth of tea plant, it is very important to understand their alteration and regulation mechanisms. In the present work, we first summarize the distribution, change characteristics of the main flavor-contributing metabolites in different cultivars, organs and under environmental stresses of tea plant. Subsequently, we discuss the regulating mechanisms involved in the biosynthesis of these metabolites based on the existing evidence. Finally, we propose the remarks and perspectives on the future study relating flavor-contributing metabolites. This review would contribute to the acceleration of research on the characteristic secondary metabolites and the breeding programs in tea plants.

Genetic transformation of legumes: an update

This review summarizes the recent advances in legume genetic transformation and provides an insight into the critical factors that play a major role in the process. It also sheds light on some of the potential areas which may ameliorate the transformation of legumes. Legumes are an important group of dicotyledonous plants, highly enriched in proteins and minerals. Majority of the legume plants are cultivated in the arid and semi-arid parts of the world, and hence said to be climate resilient. They have the capability of atmospheric nitrogen fixation and thus play a vital role in the ecological sphere. However, the worldwide production of legumes is somehow not up to the mark and the yields are greatly affected by various biotic and abiotic stress factors. Genetic engineering strategies have emerged as a core of plant biology and remarkably facilitate the crop improvement programmes. A significant progress has been made towards the optimization of efficient transformation system for legume plants over the years but this group is still underutilized in comparison to other crops. Among the variety of available DNA delivery systems, Agrobacterium-mediated and particle bombardment have been primarily deployed for optimization and trait improvement. However, recalcitrance and genotype-dependence are some of the major bottlenecks for successful transformation. In this context, the present review summarizes the advances taken place in the area of legume transformation and provides an insight into the present scenario. The challenges and future possibilities for yield improvement have also been discussed.

The Regulation of Floral Colour Change in Pleroma raddianum (DC.) Gardner

Floral colour change is a widespread phenomenon in angiosperms, but poorly understood from the genetic and chemical point of view. This article investigates this phenomenon in Pleroma raddianum, a Brazilian endemic species whose flowers change from white to purple. To this end, flavonoid compounds and their biosynthetic gene expression were profiled. By using accurate techniques (Ultra Performance Liquid Chromatography-High-Resolution Mass Spectrometry (UPLC-HRMS)), thirty phenolic compounds were quantified. Five key genes of the flavonoid biosynthetic pathway were partially cloned, sequenced, and the mRNA levels were analysed (RT-qPCR) during flower development. Primary metabolism was also investigated by gas chromatography coupled to mass spectrometry (GC-EIMS), where carbohydrates and organic acids were identified. Collectively, the obtained results suggest that the flower colour change in P. raddianum is determined by petunidin and malvidin whose accumulation coincides with the transcriptional upregulation of early and late biosynthetic genes of the flavonoid pathway, mainly CHS and ANS, respectively. An alteration in sugars, organic acids and phenolic co-pigments is observed together with the colour change. Additionally, an increment in the content of Fe³⁺ ions in the petals, from the pink to purple stage, seemed to influence the saturation of the colour.

SlMYB72 Regulates the Metabolism of Chlorophylls, Carotenoids, and Flavonoids in Tomato Fruit

Tomato (Solanum lycopersicum) fruit ripening is accompanied by the degradation of chlorophylls and the accumulation of carotenoids and flavonoids. Tomato SlMYB72 belongs to the R2R3 MYB subfamily, is located in the nucleus, and possesses transcriptional activator activity. Down-regulation of the SlMYB72 gene produced uneven-colored fruits; that is, dark green spots appeared on immature and mature green fruits, whereas yellow spots appeared on red fruits. Down-regulation of SlMYB72 increased chlorophyll accumulation, chloroplast biogenesis and development, and photosynthesis rate in fruits. This down-regulation decreased lycopene content, promoted β-carotene production and chromoplast development, and increased flavonoid accumulation in fruits. RNA sequencing analysis revealed that down-regulation of SlMYB72 altered the expression levels of genes involved in the biosynthesis of chlorophylls, carotenoids, and flavonoids. SlMYB72 protein interacted with the auxin response factor SlARF4. SlMYB72 directly targeted protochlorophyllide reductase, Mg-chelatase H subunit, and knotted1-like homeobox2 genes and regulated chlorophyll biosynthesis and chloroplast development. SlMYB72 directly bound to phytoene synthase, ζ-carotene isomerase, and lycopene β-cyclase genes and regulated carotenoid biosynthesis. SlMYB72 directly targeted 4-coumarate-coenzyme A ligase and chalcone synthase genes and regulated the biosynthesis of flavonoids and phenolic acid. The uneven color phenotype in RNA interference-SlMYB72 fruits was due to uneven silencing of SlMYB72 and uneven expression of chlorophyll, carotenoid, and flavonoid biosynthesis genes. In summary, this study identified important roles for SlMYB72 in the regulation of chlorophyll, carotenoid, and flavonoid metabolism and provided a potential target to improve fruit nutrition in horticultural crops.

Preventive Effects of Kaempferol on High-Fat Diet-Induced Obesity Complications in C57BL/6 Mice

Kaempferol is a dietary flavanol that regulates cellular lipid and glucose metabolism. Its mechanism of action in preventing hepatic steatosis and obesity-related disorders has yet to be clarified. The purpose of this research was to examine kaempferol's antiobesity effects in high-fat diet- (HFD-) fed mice and to investigate its impact on their gut microbiota. Using a completely randomized design, 30 mice were equally assigned to a control group, receiving a low-fat diet, an HFD group, receiving a high-fat diet, and an HFD+kaempferol group, receiving a high-fat diet and kaempferol doses of 200 mg/kg in the diet. After eight weeks, the HFD mice displayed substantial body and liver weight gain and high blood glucose and serum cholesterol levels. However, treatment with kaempferol moderated body and liver weight gain and elevation of blood glucose and serum cholesterol and triglyceride levels. Examination of 16S ribosomal RNA showed that HFD mice exhibited decreased microbial diversity, but kaempferol treatment maintained it to nearly the same levels as those in the control group. In conclusion, kaempferol can protect against obesity and insulin resistance in mice on a high-fat diet, partly through regulating their gut microbiota and moderating the decrease in insulin resistance.

Integrative Transcriptomic and Metabolic Analyses Provide Insights into the Role of Trichomes in Tea Plant (Camellia Sinensis)

Trichomes, which develop from epidermal cells, are regarded as one of the key features that are involved in the evaluation of tea quality and tea germplasm resources. The metabolites from trichomes have been well characterized in tea products. However, little is known regarding the metabolites in fresh tea trichomes and the molecular differences in trichomes and tea leaves per se. In this study, we developed a method to collect trichomes from tea plant tender shoots, and their main secondary metabolites, including catechins, caffeine, amino acids, and aroma compounds, were determined. We found that the majority of these compounds were significantly less abundant in trichomes than in tea leaves. RNA-Seq was used to investigate the differences in the molecular regulatory mechanism between trichomes and leaves to gain further insight into the differences in trichomes and tea leaves. In total, 52.96 Gb of clean data were generated, and 6560 differentially expressed genes (DEGs), including 4471 upregulated and 2089 downregulated genes, were identified in the trichomes vs. leaves comparison. Notably, the structural genes of the major metabolite biosynthesis pathways, transcription factors, and other key DEGs were identified and comparatively analyzed between trichomes and leaves, while trichome-specific genes were also identified. Our results provide new insights into the differences between tea trichomes and leaves at the metabolic and transcriptomic levels, and open up new doors to further recognize and re-evaluate the role of trichomes in tea quality formation and tea plant growth and development.