An in silico analysis of the key genes involved in flavonoid biosynthesis in Citrus sinensis

Transcriptomic and targeted metabolome analyses revealed the regulatory mechanisms of the synthesis of bioactive compounds in Citrus grandis 'tomentosa'

Exocarpium Citri Grandis is a popular Chinese herbal medicine prepared from Citrus grandis 'tomentosa', and it is rich in several bioactive compounds, including flavonoids, coumarins, and volatile oils. However, studies are yet to elucidate the mechanisms of synthesis and regulation of these active components. Therefore, the present study examined the profiles of flavonoids and volatile oil bioactive compounds in plant petals, fruits, and tender leaves, and then performed RNA sequencing on different tissues to identify putative genes involved in the synthesis of bioactive compounds. The results show that the naringin, naringenin, and coumarin contents of the fruitlets were significantly higher than those of the tender leaves and petals, whereas the tender leaves had significantly higher levels of rhoifolin and apigenin. A total of 49 volatile oils, of which 10 were mainly found in flowers, 15 were mainly found in fruits, and 18 were mainly found in leaves, were identified. RNA sequencing identified 9,942 genes that were differentially expressed in different tissues. Further analysis showed that 20, 15, and 74 differentially expressed genes were involved in regulating flavonoid synthesis, regulating coumarin synthesis, and synthesis and regulation of terpenoids, respectively. CHI1 (Cg7g005600) and 1,2Rhat gene (Cg1g023820) may be involved in the regulation of naringin synthesis in C. grandis fruits. The HDR (Cg8g006150) gene, HMGS gene (Cg5g009630) and GGPS (Cg1g003650) may be involved in the regulation and synthesis of volatile oils in C. grandis petals. Overall, the findings of the present study enhance our understanding of the regulatory mechanisms of secondary metabolites in C. grandis, which could promote the breeding of C. grandis with desired characteristics.

Integrated transcriptome and metabolome analysis revealed that HaMYB1 modulates anthocyanin accumulation to deepen sunflower flower color

KEY MESSAGE

HanMYB1 was found to play positive roles in the modulation of anthocyanins metabolism based on the integrative analysis of different color cultivars and the related molecular genetic analyses. As a high value ornamental and edible crop with various colors, sunflowers (Helianthus annuus L.) provide an ideal system to understand the formation of flower color. Anthocyanins are major pigments in higher plants, which is associated with development of flower colors and ability of oxidation resistance. Here, we performed an integrative analysis of the transcriptome and flavonoid metabolome in five sunflower cultivars with different flower colors. According to differentially expressed genes and differentially accumulated flavonoids, these cultivars could be grouped into yellow and red. The results showed that more anthocyanins were accumulated in the red group flowers, especially the chrysanthemin. Some anthocyanins biosynthesis-related genes like UFGT (UDP-glycose flavonoid glycosyltransferase) also expressed more in the red group flowers. A MYB transcriptional factor, HanMYB1, was found to play vital positive roles in the modulation of anthocyanins metabolism by the integrative analysis. Overexpressed HanMYB1 in tobacco could deepen the flower color, increase the accumulation of anthocyanins and directly active the express of UFGT genes. Our findings indicated that the MYB transcriptional factors provide new insight into the dynamic regulation of the anthocyanin biosynthesis in facilitating sunflower color formation and anthocyanin accumulation.

Transcriptomic and Non-Targeted Metabolomic Analyses Reveal the Flavonoid Biosynthesis Pathway in Auricularia cornea

Flavonoids, which are abundant in plants, are recognized for their antioxidant and anticancer roles in clinical applications. However, little is known about the molecular basis of flavonoid biosynthesis in fungi. In this study, we found that inclusion of leachate of Korshinsk peashrub (Caragana korshinskii) in the fermentation medium increased the total flavonoid content of the edible fungus Auricularia cornea by 23.6% relative to that grown in a control medium. Combined transcriptomic and non-targeted metabolomic analysis of the flavonoid biosynthesis pathway in A. cornea illustrated that there are important metabolites in the phenylpropanoid, coumarin and isoflavonoid biosynthesis pathways. In addition, we found that certain homologous genes encode phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO) and chalcone isomerase (CHI) in these biosynthesis pathways. These results, in this study, provide a new line for studying the regulation of flavonoid production in edible fungi.

Recent insights on gene expression studies on Hevea Brasiliensis fatal leaf fall diseases

Hevea brasiliensis is one of the most important agricultural commodities globally, heavily cultivated in Southeast Asia. Fatal leaf fall diseases cause aggressive leaf defoliation, linked to lower latex yield and death of crops before maturity. Due to the significant consequences of the disease to H. brasiliensis, the recent gene expression studies from four fall leaf diseases of H. brasiliensis were gathered; South American leaf blight, powdery mildew, Corynespora cassiicola and Phytophthora leaf fall disease. The differential analysis observed the pattern of commonly expressed genes upon fungi triggers using RT-PCR, DDRT-PCR, Real-time qRT-PCR and RNA-Seq. We have observed that RNA-Seq is the best tool to seek novel genes. Among the identified genes with defence-against fungi were pathogenesis-related genes such as β-1,3-glucanase and chitinase, the reactive oxygen species, and the phytoalexin biosynthesis. This manuscript also provided functional elaboration on the responsive genes and predicted possible biosynthetic pathways to identify and characterise novel genes in the future. At the end of the manuscript, the PCR methods and proteomic approaches were presented for future molecular and biochemical studies in the related diseases to H. brasiliensis.

Agrobacterium rhizogenes-mediated transformation enhances the antioxidant potential of Artemisia tilesii Ledeb

Plants belonging to the genus Artemisia L. have been used for medicinal purposes since ancient times. These aromatic plants produce and accumulate a wide range of potent secondary metabolites, many of which have shown antioxidant, antiparasitic, antimicrobial, anti-inflammatory, and even anticancer activities. Enhanced biosynthesis of these compounds is a prerequisite for comprehensive studies of their therapeutic properties and cost-efficient use. Transformation of plants with Agrobacterium rhizogenes native root locus (rol) genes is a promising approach to increase the biosynthesis of plant secondary metabolites. The aim of the present study was to evaluate the effects of A. rhizogenes-mediated transformation on the flavonoid contents in hairy roots of medicinal herb A. tilesii Ledeb. Transgenic A. tilesii hairy root lines were analyzed for stable integration of the rolB and rolC transgenes into the plant genome, total flavonoid contents, antioxidant activities of extracts, and the spatiotemporal expression of two flavonoid biosynthetic genes, phenylalanine ammonialyase (PAL) and chalcone synthase (CHS). The flavonoid contents of A. tilesii directly correlated with the antiradical activity and reducing power of their respective lines, with the greatest antioxidant activity found in the plants with the highest level of total flavonoids. Furthermore, all hairy root lines demonstrated altered expression of plant native PAL and CHS genes. Most importantly, A. rhizogenes-mediated transformation enhanced the biosynthesis of natural antioxidants in A. tilesii, producing almost twice the amount of flavonoids than controls. These findings provide an opportunity for the identification of the bioactive molecules in A. tilesii extracts and their potential health benefits.

Genome-wide Expression Analysis and Metabolite Profiling Elucidate Transcriptional Regulation of Flavonoid Biosynthesis and Modulation under Abiotic Stresses in Banana

Flavonoid biosynthesis is largely regulated at the transcriptional level due to the modulated expression of genes related to the phenylpropanoid pathway in plants. Although accumulation of different flavonoids has been reported in banana, a staple fruit crop, no detailed information is available on regulation of the biosynthesis in this important plant. We carried out genome-wide analysis of banana (Musa acuminata, AAA genome) and identified 28 genes belonging to 9 gene families associated with flavonoid biosynthesis. Expression analysis suggested spatial and temporal regulation of the identified genes in different tissues of banana. Analysis revealed enhanced expression of genes related to flavonol and proanthocyanidin (PA) biosynthesis in peel and pulp at the early developmental stages of fruit. Genes involved in anthocyanin biosynthesis were highly expressed during banana fruit ripening. In general, higher accumulation of metabolites was observed in the peel as compared to pulp tissue. A correlation between expression of genes and metabolite content was observed at the early stage of fruit development. Furthermore, this study also suggests regulation of flavonoid biosynthesis, at transcriptional level, under light and dark exposures as well as methyl jasmonate (MJ) treatment in banana.

Rol genes enhance the biosynthesis of antioxidants in Artemisia carvifolia Buch

BACKGROUND

The secondary metabolites of the Artemisia genus are well known for their important therapeutic properties. This genus is one of the valuable sources of flavonoids and other polyphenols, but due to the low contents of these important metabolites, there is a need to either enhance their concentration in the original plant or seek alternative sources for them. The aim of the current study was to detect and enhance the yield of antioxidant compounds of Artemisia carvifolia Buch. HPLC analysis was performed to detect the antioxidants. With the aim of increasing flavonoid content, Rol gene transgenics of A. carvifolia were established. Two genes of the flavonoid biosynthetic pathway, phenylalanine ammonia-lyase and chalcone synthase, were studied by real time qPCR. Antioxidant potential was determined by performing different antioxidant assays.

RESULTS

HPLC analysis of wild-type A. carvifolia revealed the presence of flavonoids such as caffeic acid (30 μg/g DW), quercetin (10 μg/g DW), isoquercetin (400 μg/g DW) and rutin (300 μg/g DW). Compared to the untransformed plants, flavonoid levels increased 1.9-6-fold and 1.6-4-fold in rol B and rol C transgenics, respectively. RT qPCR analysis showed a variable expression of the flavonoid biosynthetic genes, including those encoding phenylalanine ammonia-lyase and chalcone synthase, which were found to be relatively more expressed in transformed than wild-type plants, thus correlating with the metabolite concentration. Methanolic extracts of transgenics showed higher antioxidant capacity, reducing power, and protection against free radical-induced DNA damage. Among the transgenic plants, those harboring rol B were slightly more active than the rol C-transformants.

CONCLUSION

As well as demonstrating the effectiveness of rol genes in inducing plant secondary metabolism, this study provides insight into the molecular dynamics of the flavonoid accumulation pattern, which correlated with the expression of biosynthetic genes.

The State of the Art in Biosynthesis of Anthocyanins and Its Regulation in Pigmented Sweet Oranges [(Citrus sinensis) L. Osbeck]

Anthocyanins are water-soluble pigments belonging to the flavonoid compound family involved in nature in several aspects of plant development and defense. By bestowing much of the color and flavor on fruits and vegetables, they are components of the human diet and, thanks to their radical-scavenging properties, are not considered exclusively as food products but also as therapeutic agents. Several cultivars of red (or blood) oranges [Citrus sinensis (L.) Osbeck], such as Tarocco, Moro, and Sanguinello, are characterized by the presence of anthocyanins in both the rind and fruit juice vesicles. The amount and composition of anthocyanins in the pigmented orange cultivar vary greatly depending on variety, maturity, region of cultivation, and many other environmental conditions. Most of the blood orange varieties require a wide day-night thermal range to maximize color formation. Therefore, the production of red oranges characterized by high anthocyanin levels is limited to a few regions and in particular to the Sicilian area around Mount Etna in Italy, where the characteristic climate conditions yield fruits of unique color intensity and quality. In this review, both the basic information and the most recent advances in red orange anthocyanins are reported, with intense attention given to their biosynthesis and regulation.

Phenylpropanoid Metabolism in Ripening Fruits

  Ripening of fleshy fruit is a differentiation process involving biochemical and biophysical changes that lead to the accumulation of sugars and subsequent changes in tissue texture. Also affected are phenolic compounds, which confer color, flavor/aroma, and resistance to pathogen invasion and adverse environmental conditions. These phenolic compounds, which are the products of branches of the phenylpropanoid pathway, appear to be closely linked to fruit ripening processes. Three key enzymes of the phenylpropanoid pathway, namely phenylalanine ammonia lyase, O-methyltransferase, and cinnamyl alcohol dehydrogenase (CAD) have been reported to modulate various end products including lignin and protect plants against adverse conditions. In addition, peroxidase, the enzyme following CAD in the phenylpropanoid pathway, has also been associated with injury, wound repair, and disease resistance. However, the role of these enzymes in fruit ripening is a matter of only recent investigation and information is lacking on the relationships between phenylpropanoid metabolism and fruit ripening processes. Understanding the role of these enzymes in fruit ripening and their manipulation may possibly be valuable for delineating the regulatory network that controls the expression of ripening genes in fruit. This review elucidates the functional characterization of these key phenylpropanoid biosynthetic enzymes/genes during fruit ripening processes.