The accumulation and localization of chalcone synthase in grapevine (Vitis vinifera L.)

Soybean AROGENATE DEHYDRATASES (GmADTs): involvement in the cytosolic isoflavonoid metabolon or trans-organelle continuity?

Soybean (Glycine max) produces a class of phenylalanine (Phe) derived specialized metabolites, isoflavonoids. Isoflavonoids are unique to legumes and are involved in defense responses in planta, and they are also necessary for nodule formation with nitrogen-fixing bacteria. Since Phe is a precursor of isoflavonoids, it stands to reason that the synthesis of Phe is coordinated with isoflavonoid production. Two putative AROGENATE DEHYDRATASE (ADT) isoforms were previously co-purified with the soybean isoflavonoid metabolon anchor ISOFLAVONE SYNTHASE2 (GmIFS2), however the GmADT family had not been characterized. Here, we present the identification of the nine member GmADT family. We determined that the GmADTs share sequences required for enzymatic activity and allosteric regulation with other characterized plant ADTs. Furthermore, the GmADTs are differentially expressed, and multiple members have dual substrate specificity, also acting as PREPHENATE DEHYDRATASES. All GmADT isoforms were detected in the stromules of chloroplasts, and they all interact with GmIFS2 in the cytosol. In addition, GmADT12A interacts with multiple other isoflavonoid metabolon members. These data substantiate the involvement of GmADT isoforms in the isoflavonoid metabolon.

Integrative analysis of grapevine (Vitis vinifera L) transcriptome reveals regulatory network for Chardonnay quality formation

Anthocyanins, total phenols, soluble sugar and fruit shape plays a significant role in determining the distinct fruit quality and customer preference. However, for the majority of fruit species, little is known about the transcriptomics and underlying regulatory networks that control the generation of overall quality during fruit growth and ripening. This study incorporated the quality-related transcriptome data from 6 ecological zones across 3 fruit development and maturity phases of Chardonnay cultivars. With the help of this dataset, we were able to build a complex regulatory network that may be used to identify important structural genes and transcription factors that control the anthocyanins, total phenols, soluble sugars and fruit shape in grapes. Overall, our findings set the groundwork to improve grape quality in addition to offering novel views on quality control during grape development and ripening.

Molecular characterization of a chalcone synthase gene RhCHS from Rhododendron × hybridum Hort

Chalcone synthase (CHS) plays a vital role in anthocyanin biosynthesis pathway, which is associated with petal color of flower. To date, lots of CHS genes have been obtained from plants, while few were from Rhododendron genus. In this study we got a new CHS gene named RhCHS (MW358095) from Rhododendron × hybridum Hort. It had a 2040 bp coding region consisting of two exons and one intron. By using the deduced RhCHS protein as a query sequence, 15 CHS homologous family genes with sequence similarity from 60% to 98%, designated as RgCHS-D(x), were retrieved from the genome assembly of Rhododendron griersonianum (RGv1.1) by TBlastN. 12 CHS family genes were found locating in No.9 chromosome arranged in clusters, while only 3 of them exhibited in No.1, 2, and 8 chromosomes, respectively. The results revealed gene duplication of CHS in evolutionary process. Multiple alignment of the deduced amino acid sequence of RhCHS showed high similarity of the active site, the catalytic residue, and the signature motif, the conserved characteristics of which were also exhibited in the tertiary structure prediction of the RhCHS, as well as the phylogenetic tree, all these demonstrated the RhCHS belonging to the type III PKS superfamily. HPLC-MS/MS of flower petals detected the total concentration of CC, DC, and PelC. These anthocyanidins showed an overall increasing trend during the flowering period and reached the peak in the full-blooming stage, which was consistence with the changeable rule of RhCHS expression level. The promoter, which was 1507 bp exhibiting high β-glucuronidase (GUS) staining activity, was predicted containing many cis-acting elements, especially light and transcription factor such as bHLH, MYB, WRKY, Dof, and ERF. In short, this study may provide the help to Rhododendron × hybridum Hort. not only in the mechanism research of petals color exhibition, but also in molecular breeding of CHS practice value.

Physiological and Transcriptional Responses to Saline Irrigation of Young 'Tempranillo' Vines Grafted Onto Different Rootstocks

The use of more salt stress-tolerant vine rootstocks can be a sustainable strategy for adapting traditional grapevine cultivars to future conditions. However, how the new M1 and M4 rootstocks perform against salinity compared to conventional ones, such as the 1103-Paulsen, had not been previously assessed under real field conditions. Therefore, a field trial was carried out in a young 'Tempranillo' (Vitis vinifera L.) vineyard grafted onto all three rootstocks under a semi-arid and hot-summer Mediterranean climate. The vines were irrigated with two kinds of water: a non-saline Control with EC of 0.8 dS m-1 and a Saline treatment with 3.5 dS m-1. Then, various physiological parameters were assessed in the scion, and, additionally, gene expression was studied by high throughput sequencing in leaf and berry tissues. Plant water relations evidenced the osmotic effect of water quality, but not that of the rootstock. Accordingly, leaf-level gas exchange rates were also reduced in all three rootstocks, with M1 inducing significantly lower net photosynthesis rates than 1103-Paulsen. Nevertheless, the expression of groups of genes involved in photosynthesis and amino acid metabolism pathways were not significantly and differentially expressed. The irrigation with saline water significantly increased leaf chloride contents in the scion onto the M-rootstocks, but not onto the 1103P. The limitation for leaf Cl- and Na+ accumulation on the scion was conferred by rootstock. Few processes were differentially regulated in the scion in response to the saline treatment, mainly, in the groups of genes involved in the flavonoids and phenylpropanoids metabolic pathways. However, these transcriptomic effects were not fully reflected in grape phenolic ripeness, with M4 being the only one that did not cause reductions in these compounds in response to salinity, and 1103-Paulsen having the highest overall concentrations. These results suggest that all three rootstocks confer short-term salinity tolerance to the scion. The lower transcriptomic changes and the lower accumulation of potentially phytotoxic ions in the scion grafted onto 1103-Paulsen compared to M-rootstocks point to the former being able to maintain this physiological response in the longer term. Further agronomic trials should be conducted to confirm these effects on vine physiology and transcriptomics in mature vineyards.

Transcriptome sequencing and metabolomics analyses provide insights into the flavonoid biosynthesis in Torreya grandis kernels

The kernel of Torreya grandis (T. grandis) is a rare nut with a variety of bioactive compounds. Flavonoids are a very important class of bioactive compounds with high antioxidant activity in T. grandis kernels. However, the flavonoid compositions which mainly contribute to antioxidant capacity and the molecular basis of flavonoid biosynthesis in T. grandis remain unclear. Here, transcriptome sequencing and metabolomics analysis for kernels were performed. In total, 124 flavonoids were identified. Among them, 9 flavonoids were highly correlated with antioxidant activity. Furthermore, unigenes encoding CHS, DFR and ANS showed significant correlation with the 9 flavonoids. Transient overexpression of TgDFR1 in tobacco leaves resulted in increased antioxidant activity. Moreover, several transcription factors from MYB, bHLH and bZIP families were identified by co-expression assay, suggesting that they may regulate flavonoid biosynthesis. Our findings provide a molecular basis and new insights into the flavonoid biosynthesis in T. grandis kernels.

In silico identification of Capsicum type III polyketide synthase genes and expression patterns in Capsicum annuum

Studies have shown that abundant and various flavonoids accumulate in chili pepper (Capsicum), but there are few reports on the genes that govern chili pepper flavonoid biosynthesis. Here, we report the comprehensive identification of genes encoding type III polyketide synthase (PKS), an important enzyme catalyzing the generation of flavonoid backbones. In total, 13, 14 and 13 type III PKS genes were identified in each genome of C. annuum, C. chinense and C. baccatum, respectively. The phylogeny topology of Capsicum PKSs is similar to those in other plants, as it showed two classes of genes. Within each class, clades can be further identified. Class II genes likely encode chalcone synthase (CHS) as they are placed together with the Arabidopsis CHS gene, which experienced extensive expansions in the genomes of Capsicum. Interestingly, 8 of the 11 Class II genes form three clusters in the genome of C. annuum, which is likely the result of tandem duplication events. Four genes are not expressed in the tissues of C. annuum, three of which are located in the clusters, indicating that a portion of genes was pseudogenized after tandem duplications. Expression of two Class I genes was complementary to each other, and all the genes in Class II were not expressed in roots of C. annuum. Two Class II genes (CA00g90790 and CA05g17060) showed upregulated expression as the chili pepper leaves matured, and two Class II genes (CA05g17060 and CA12g20070) showed downregulated expression with the maturation of fruits, consistent with flavonoid accumulation trends in chili pepper as reported previously. The identified genes, sequences, phylogeny and expression information collected in this article lay the groundwork for future studies on the molecular mechanisms of chili pepper flavonoid metabolism.

The influence of downy mildew tolerance of grape varieties on the biosynthesis of stilbenes in callus as potential sources of bioactive substances

Stilbenes represent a considerable practical interest in relation to their benifits to the human health. Callus culture of the grape, which is a natural producer of stilbenes, can serve as an effective source of these compounds. Grape’s resistance to biotic environmental stress conditions is associated with the synthesis and conversion of stilbenes, therefore the aim of the current study was to determine an interrelation between the tolerance of grape varieties to downy mildew and stilbene biosynthesis in the callus culture. Obtained results showed that there was no link between variety’s tolerance to downy mildew and content of stilbenes, chalcones and phenoloxydising enzymes in callus. Presence of the stress impact is a necessary condition for the initiation of the variety-specific synthesis of stilbenes. Callus of varieties, in which stilbenes content was higher, was characterized by a lowered expression of the chalcone synthase and chalcone isomerase relative to expression of genes of the stilbene synthase and phenylalanine ammonia liase, which confirms an interrelation between reduced competition for the substrate between two biosynthesis branches of chalcones and stilbenes with production of the latter.

Chalcone synthases (CHSs): the symbolic type III polyketide synthases

Present review provides a thorough insight on some significant aspects of CHSs over a period of about past three decades with a better outlook for future studies toward comprehending the structural and mechanistic intricacy of this symbolic enzyme. Polyketide synthases (PKSs) form a large family of iteratively acting multifunctional proteins that are involved in the biosynthesis of spectrum of natural products. They exhibit remarkable versatility in the structural configuration and functional organization with an incredible ability to generate different classes of compounds other than the characteristic secondary metabolite constituents. Architecturally, chalcone synthase (CHS) is considered to be the simplest representative of Type III PKSs. The enzyme is pivotal for phenylpropanoid biosynthesis and is also well known for catalyzing the initial step of the flavonoid/isoflavonoid pathway. Being the first Type III enzyme to be discovered, CHS has been subjected to ample investigations which, to a greater extent, have tried to understand its structural complexity and promiscuous functional behavior. In this context, we vehemently tried to collect the fragmented information entirely focussed on this symbolic enzyme from about past three-four decades. The aim of this review is to selectively summarize data on some of the fundamental aspects of CHSs viz, its history and distribution, localization, structure and analogs in non-plant hosts, promoter analyses, and role in defense, with an emphasis on mechanistic studies in different species and vis-à-vis mutation-led changes, and evolutionary significance which has been discussed in detail. The present review gives an insight with a better perspective for the scientific community for future studies devoted towards delimiting the mechanistic and structural basis of polyketide biosynthetic machinery vis-à-vis CHS.

Molecular cloning and functional characterization of chalcone isomerase from Carthamus tinctorius

Flavonoid is one of the widespread groups of plant secondary metabolites that provide several health benefits. However, the explicit mechanism of flavonoid biosynthesis in plants largely remains unclear. Chalcone isomerase an important class of enzyme presents crucial role during flavonoid metabolism in many plants. Here, we isolated the full-length cDNA (1161 bp) of a novel Chalcone Isomerase from safflower encoding 217 amino acid polypeptide using oligos from 5′ and 3′ ends. The result of Sanger sequencing and phylogenetic analysis revealed that CtCHI is highly homologous to other plants, including typical polyadenylation signals AATAA and Poly A tail. The transient expression in tobacco mesophyll cells using Green Fluorescent Protein tagging determined the subcellular localization of CtCHI in cell membrane and nucleus. The CtCHI ectopic expression in different safflower varieties at different flowering stages showed that CtCHI were found in abundance at the bud stage of Jihong No. 1. Further correlation analysis between CtCHI expression and flavonoid accumulation at various flowering phases suggested that CtCHI might play a potential role during flavonoid biosynthesis in safflower. In addition, the overexpression of pBASTA-CtCHI in transgenic Arabidopsis infiltrated with floral dip transformation showed relatively higher expression level and increased flavonoid accumulation than wild type. Moreover, the in vitro enzymatic activity and HPLC analysis of transgenic Arabidopsis confirmed the de novo biosynthesis of Rutin. Taken together, our findings laid the foundation of identifying an important gene that might influence flavonoid metabolism in safflower.

Rice sulfoquinovosyltransferase SQD2.1 mediates flavonoid glycosylation and enhances tolerance to osmotic stress

Sulfoquinovosyltransferase 2 (SQD2) catalyses the final step in the sulfoquinovosyldiacylglycerol (SQDG) biosynthetic pathway. It is involved in the phosphate starvation response. Here, we show that rice SQD2.1 has dual activities catalysing SQDG synthesis and flavonoid glycosylation. SQD2.1 null mutants (sqd2.1) in rice had decreased levels of glycosidic flavonoids, particularly apigenin 7-O-glucoside (A7G), whereas these metabolites were increased in rice plants overexpressing SQD2.1. The sqd2.1 mutants and SQD2.1 overexpressing lines showed reduced and enhanced, respectively, tolerance to salinity and drought. Treating the sqd2.1 mutants with A7G decreased oxidative damage and restored stress tolerance to the wild-type levels. These findings demonstrate that SQD2.1 has a novel function in the glycosylation of flavonoids that is required for osmotic stress tolerance in rice. The novel activity of SQD2.1 in the production of glycosidic flavonoids improves scavenging of reactive oxygen species and protects against excessive oxidation.

Isolation and characterization of a novel chalcone synthase gene family from mulberry

Chalcone synthase (CHS) is the pivotal enzyme that catalyzes the first committed step of the phenylpropanoid pathway leading to flavonoids. Here, five CHS genes were determined in mulberry (Morus atropurpurea Roxb.). Interestingly, phylogenetic analysis tended to group three MaCHSs in the stilbene synthase (STS) family and initially annotated these as MaSTSs. A co-expression system that harbored a 4-coumarate:CoA ligase gene and one of the candidate genes was established to determine the functions of this novel gene family. The fermentation result demonstrated that MaSTS in fact encoded a CHS enzyme, and was consequently retermed MaCHS. Tissue-specific expression analysis indicated that MaCHS1/MaCHS2 was highly abundant in fruit, and MaCHS4 had significant expression in root bark, stem bark and old leaves, while MaCHS3 and MaCHS5 were more expressed in old leaves. Subcellular localization experiments showed that MaCHS was localized to the cytoplasm. Transcription levels suggested MaCHS genes were involved in a series of defense responses. Over-expression of MaCHS in transgenic tobacco modified the metabolite profile, and resulted in elevated tolerance to a series of environmental stresses. This study comprehensively evaluated the function of MaCHS genes and laid the foundation for future research on MaCHS in mulberry.