Isolation and characterization of chalcone synthase gene isolated from Dendrobium Sonia Earsakul

Polyketide synthases (PKSs) of secondary metabolism: in silico identification and characterization in orchids

Type III polyketide synthases (PKSs) catalyse the formation of an array of polyketides with diverse structures that play an important role in secondary metabolism in plants. This group of enzymes is encoded by a multigene family, the Type III polyketide synthase (PKS) gene family. Vast reserves of secondary metabolites in orchids make these plants suitable candidates for research in the area. In this study, genome-wide searches lead to the identification of five PeqPKS, eight DcaPKS and six AshPKS genes in Phalaenopsis equestris, Dendrobium catenatum and Apostasia shenzhenica, respectively. All the members showed the presence of two characteristic conserved domains (Chal_sti_synt_N and Chal_sti_synt_C) and were generally localised in the cytoplasm. The phylogenetic analysis led to the classification of these proteins into two groups: CHS (chalcone synthase (CHS) and non-CHS. A single protein in P. equestris and two proteins each in D. catenatum and A. shenzhenica clustered within the CHS clade. The majority of the genes exhibited similar structural patterns with a single intron. Expression profiling revealed the tissue-specific expression of these genes with high expression in reproductive tissues for most genes. A number of stress-responsive cis-regulatory elements were predicted, noteworthy amongst these are, ABRE and CGTCA that are chiefly responsible for responding to abscisic acid and methyl jasmonate, respectively. Our study provides a reference framework for future studies involving functional elucidation of PKS genes and biotechnological production of polyketides.Communicated by Ramaswamy H. Sarma.

Effect of gamma rays and colchicine on silymarin production in cell suspension cultures of Silybum marianum: A transcriptomic study of key genes involved in the biosynthetic pathway

The aim of this study was to investigate secondary metabolite production in Silybum marianum L. cell suspension cultures obtained from seeds treated with gamma rays (200 and 600 Gy) and 0.05% colchicine. The effects of these treatments on callus induction, growth, viability, and silymarin production were studied, along with the changes in the transcriptome and DNA sequence of chalcone synthase (CHS) genes. The effect of gamma radiation (200 and 600 Gy) on silymarin production in S. marianum dry seeds was also studied using HPLC-UV. All three treatments induced high callus biomass production from leaf segments. The viability of the cell suspension cultures was over 90%. The flavonolignan content measured in the extracellular culture medium of the S. marianum cell suspension was highest after treatment with 600 Gy, followed by 0.05% colchicine, and finally, 200 Gy, after a growth period of 12 days. In general, an increased expression of CHS1, CHS2, and CHS3 genes, accompanied by an increase of silymarin content, was observed in response to all the studied treatments, although the effect was greatest on CHS2 expression. Bioinformatics analysis confirmed that the three CHS2 clones exhibited the highest genetic variation, both in relation to each other and to the CHS1 and CHS3 clones. Based on the results, S. marianum plants obtained from seeds previously exposed to 600 and 200 Gy as well as colchicine constitute a renewable resource with the potential to obtain large amounts of silymarin.

Molecular cloning and characterization of chalcone synthase gene from Coelogyne ovalis Lindl. and its stress-dependent expression

Chalcone synthase (CHS, EC 2.3.1.74) is one of the key and rate-limiting enzymes of phenylpropanoid pathway which plays superior roles in the production of secondary metabolites. In the present study a full-length cDNA of CHS gene was isolated and characterized from Coelogyne ovalis, an orchid of ornamental and medicinal importance. The CHS gene sequence from C. ovalis (CoCHS) was found to be 1445 bp and comprised an open reading frame of 1182 bp, encoding for 394 amino acid residues. Further, the sequence alignment and phylogenetic analysis revealed that CoCHS protein shared high degree of similarity with CHS protein of other orchid species. It also confirmed that it contained all four motifs (I to IV) and signature sequence for the functionality of this gene. Structural modeling of CoCHS based on the crystallographic structure of Freesia hybrida indicated that CoCHS had a similar structure. Quantitative polymerase chain reaction (qPCR) disclosed that CoCHS was expressed in all tissues examined, with the highest transcript being in leaves, followed by pseudobulbs and roots. CoCHS expression was also evaluated in the in vitro-raised plantlets under the abiotic stress (dark, cold, UV-B, wounding, salinity). mRNA transcript expression of CHS gene was found to be positively enhanced and regulated by the different stress types. A correlation between the CoCHS transcript expression with flavonoid and anthocyanin contents revealed that a positive correlation existed between metabolites' content and CoCHS expression within the in vivo as well as in the in vitro-raised plant parts.

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.

Segmental and tandem chromosome duplications led to divergent evolution of the chalcone synthase gene family in Phalaenopsis orchids

BACKGROUND AND AIMS

Orchidaceae is a large plant family, and its extraordinary adaptations may have guaranteed its evolutionary success. Flavonoids are a group of secondary metabolites that mediate plant acclimation to challenge environments. Chalcone synthase (CHS) catalyses the initial step in the flavonoid biosynthetic pathway. This is the first chromosome-level investigation of the CHS gene family in Phalaenopsis aphrodite and was conducted to elucidate if divergence of this gene family is associated with chromosome evolution.

METHODS

Complete CHS genes were identified from our whole-genome sequencing data sets and their gene expression profiles were obtained from our transcriptomic data sets. Fluorescence in situ hybridization (FISH) was conducted to position five CHS genes to high-resolution pachytene chromosomes.

KEY RESULTS

The five Phalaenopsis CHS genes can be classified into three groups, PaCHS1, PaCHS2 and the tandemly arrayed three-gene cluster, which diverged earlier than those of the orchid genera and species. Additionally, pachytene chromosome-based FISH mapping showed that the three groups of CHS genes are localized on three distinct chromosomes. Moreover, an expression analysis of RNA sequencing revealed that the five CHS genes had highly differentiated expression patterns and its expression pattern-based clustering showed high correlations between sequence divergences and chromosomal localizations of the CHS gene family in P. aphrodite.

CONCLUSIONS

Based on their phylogenetic relationships, expression clustering analysis and chromosomal distributions of the five paralogous PaCHS genes, we proposed that expansion of this gene family in P. aphrodite occurred through segmental duplications, followed by tandem duplications. These findings provide information for further studies of CHS functions and regulations, and shed light on the divergence of an important gene family in orchids.

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.

De novo transcriptome of safflower and the identification of putative genes for oleosin and the biosynthesis of flavonoids

Safflower (Carthamus tinctorius L.) is one of the most extensively used oil crops in the world. However, little is known about how its compounds are synthesized at the genetic level. In this study, Solexa-based deep sequencing on seed, leaf and petal of safflower produced a de novo transcriptome consisting of 153,769 unigenes. We annotated 82,916 of the unigenes with gene annotation and assigned functional terms and specific pathways to a subset of them. Metabolic pathway analysis revealed that 23 unigenes were predicted to be responsible for the biosynthesis of flavonoids and 8 were characterized as seed-specific oleosins. In addition, a large number of differentially expressed unigenes, for example, those annotated as participating in anthocyanin and chalcone synthesis, were predicted to be involved in flavonoid biosynthesis pathways. In conclusion, the de novo transcriptome investigation of the unique transcripts provided candidate gene resources for studying oleosin-coding genes and for investigating genes related to flavonoid biosynthesis and metabolism in safflower.

Expression of flavonoid biosynthesis genes vis-à-vis rutin content variation in different growth stages of Fagopyrum species

Buckwheat is one of the field crops with the highest concentration of rutin, an important flavonoid of medicinal value. Two species of buckwheat, Fagopyrum esculentum and Fagopyrum tataricum, are the major sources of rutin. Seeds of latter contain 40-50× higher rutin compared to the former. The physiological and molecular bases of rutin content variation between Fagopyrum species are not known. The current study investigated the differences in rutin content in seeds and in other tissues and growth stages of two Fagopyrum species, and also correlated those differences with the expression of flavonoid pathway genes. The analysis of rutin content dynamics at different growth stages, S1-S9 (from seed germination to mature seed formation) of Fagopyrum species revealed that rutin content was higher during seedling stages of F. tataricum (3.5 to 4.6-fold) compared to F. esculentum and then increased exponentially from stages S3 to S6 (different leaf maturing stages and inflorescence) of F. esculentum, whereas it fluctuated in F. tataricum. The rutin content was highest in the inflorescence stage (S6) of both species, with a relatively higher biosynthesis and accumulation during post-flowering stages of F. tataricum compared to F. esculentum. The expression of flavonoid pathway genes, through qRT-PCR, in different growth stages vis-à-vis rutin content variation showed differential expression for four genes, PAL, CHS, CHI and FLS with the amounts of transcripts relatively higher in F. tataricum compared to F. esculentum, thereby, correlating these genes with the biosynthesis and accumulation of rutin. The expression of PAL was highest, 7.69 and 8.96-fold in Stages 2 (seedling stage) and 9 (fully developed seeds) of F. tataricum compared to F. esculentum, respectively. The expression of the CHS gene correlated with the rutin content because it was highest in the flowers (S6) and fully developed seeds (S9) of both Fagopyrum species, with relatively higher transcript amounts (2.13 and 3.19-fold, respectively) in F. tataricum (IC-329457) compared to F. esculentum (IC-540858). This study provides useful information on molecular and physiological dynamics of rutin biosynthesis and accumulation in Fagopyrum species and the correlation of expression of flavonoid biosynthesis genes with the rutin content can be useful in planning for genetic improvement.