Molecular cloning and characterization of phenylalanine ammonia-lyase and cinnamate 4-hydroxylase in the phenylpropanoid biosynthesis pathway in garlic (Allium sativum)

Genome-wide identification and analysis of the PAL genes from the orchids Apostasia shenzhenica, Dendrobium catenatum and Phalaenopsis equestris

Phenylalanine ammonia-lyase (PAL) is a key gateway enzyme that connects the phenylpropanoid pathway to primary metabolism. The phenylpropanoid pathway plays a vital role in the growth and environmental adaptation of many plants leading to the production of valuable bioactive compounds with industrial and medical applications. In the present study, nine putative PAL genes from three orchids were identified; five in Apostasia shenzhenica and two each in Dendrobium catenatum and Phalaenopsis equestris. Eighteen motifs and four major conserved functional domains were identified as reported in PAL proteins of other species. All the nine PALs were stable based on their computed physicochemical properties and localized in the cytoplasm. The three-dimensional structures of PALs revealed a homo-tetrameric structure consisting of four identical subunits. A total of 21 cis-regulatory elements with known functions were identified from the promoter regions of all PALs which are responsible for various plant responses to light, stress and growth regulators like auxins, gibberellins and abscisic acid. Phylogenetic analysis showed that the studied PAL proteins clustered in two major clades (clade I and II), placing dicot and monocot PALs in two separate monophyletic clades. In silico gene expression of the identified PALs in different vegetative and reproductive tissues revealed the differential expressions based on tissue type and disclosed that the expression of PAL genes was upregulated in all the tissues examined with an exception of PePAL leaf samples where no expression was detected, however, the same being highly expressed in reproductive tissues (PePAL1-labellum; PePAL2-sepal). In case of AsPALs, the expression was found to be highest in reproductive tissues (AsPAL4-maximum in inflorescence). On the other hand, the expression of DcPALs was found to be highest in vegetative tissues (DcPAL2-maximum in root). Based on the medicinal importance of orchids and the significant role of PAL genes in synthesis of bioactive compounds, the functional characterization of PAL genes can be further exploited in genetic improvement of medicinal orchids.Communicated by Ramaswamy H. Sarma.

A phenylalanine ammonia lyase from Fritillaria unibracteata promotes drought tolerance by regulating lignin biosynthesis and SA signaling pathway

Drought is one of the key threatening environmental factors for plant and agriculture. Phenylalanine ammonia lyase (PAL) is a key enzyme involved in plant defense against abiotic stress, however, the role of PAL in drought tolerance remains elusive. Here, a PAL member (FuPAL1) containing noncanonical Ala-Ser-Gly triad was isolated from Fritillaria unibracteata, one important alpine pharmaceutical plant. FuPAL1, mainly distributed in cytosol, was more conserved than FuCOMT and FuCHI at both nucleotide and amino acid levels. FuPAL1 was overexpressed in Escherichia coli and the purified recombinant FuPAL1 protein showed catalytic preference on L-Phe than L-Tyr. Homology modeling and site-mutation of FuPAL1 exhibited FuPAL1 took part in the ammonization process by forming MIO-like group, and Phe141, Ser208, Ileu218 and Glu490 played key roles in substrate binding and (or) catalysis. HPLC analysis showed that lignin and salicylic acid levels increased but total flavonoid levels decreased in FuPAL1 transgenic Arabidopsis compared to wild-type plants. Moreover, FuPAL1 transgenic Arabidopsis significantly enhanced its drought tolerance, which suggested that FuPAL1 mediated tolerance to drought by inducing the biosynthesis and accumulation of salicylic acid and lignin. Taken together, our results confirmed that the FuPAL1 played an important role in drought tolerance, and FuPAL1 might be a valuable target for genetic improvement of drought resistance in future.

Tissue-specific transcriptome analyses reveal candidate genes for stilbene, flavonoid and anthraquinone biosynthesis in the medicinal plant Polygonum cuspidatum

BACKGROUND

Polygonum cuspidatum Sieb. et Zucc. is a well-known medicinal plant whose pharmacological effects derive mainly from its stilbenes, anthraquinones, and flavonoids. These compounds accumulate differentially in the root, stem, and leaf; however, the molecular basis of such tissue-specific accumulation remains poorly understood. Because tissue-specific accumulation of compounds is usually associated with tissue-specific expression of the related biosynthetic enzyme genes and regulators, we aimed to clarify and compare the transcripts expressed in different tissues of P. cuspidatum in this study.

RESULTS

High-throughput RNA sequencing was performed using three different tissues (the leaf, stem, and root) of P. cuspidatum. In total, 80,981 unigenes were obtained, of which 40,729 were annotated, and 21,235 differentially expressed genes were identified. Fifty-four candidate synthetase genes and 12 transcription factors associated with stilbene, flavonoid, and anthraquinone biosynthetic pathways were identified, and their expression levels in the three different tissues were analyzed. Phylogenetic analysis of polyketide synthase gene families revealed two novel CHS genes in P. cuspidatum. Most phenylpropanoid pathway genes were predominantly expressed in the root and stem, while methylerythritol 4-phosphate and isochorismate pathways for anthraquinone biosynthesis were dominant in the leaf. The expression patterns of synthase genes were almost in accordance with metabolite profiling in different tissues of P. cuspidatum as measured by high-performance liquid chromatography or ultraviolet spectrophotometry. All predicted transcription factors associated with regulation of the phenylpropanoid pathway were expressed at lower levels in the stem than in the leaf and root, but no consistent trend in their expression was observed between the leaf and the root.

CONCLUSIONS

The molecular knowledge of key genes involved in the biosynthesis of P. cuspidatum stilbenes, flavonoids, and anthraquinones is poor. This study offers some novel insights into the biosynthetic regulation of bioactive compounds in different P. cuspidatum tissues and provides valuable resources for the potential metabolic engineering of this important medicinal plant.

Full-length transcriptome analysis and identification of genes involved in asarinin and aristolochic acid biosynthesis in medicinal plant Asarum sieboldii

Asarum sieboldii, a well-known traditional Chinese medicinal herb, is used for curing inflammation and ache. It contains both the bioactive ingredient asarinin and the toxic compound aristolochic acid. To address further breeding demand, genes involved in the biosynthetic pathways of asarinin and aristolochic acid should be explored. Therefore, the full-length transcriptome of A. sieboldii was sequenced using PacBio Iso-Seq to determine the candidate transcripts that encode the biosynthetic enzymes of asarinin and aristolochic acid. In this study, 63 023 full-length transcripts were generated with an average length of 1371 bp from roots, stems, and leaves, of which 49 593 transcripts (78.69%) were annotated against public databases. Furthermore, 555 alternative splicing (AS) events, 10 869 long noncoding RNAs (lncRNAs) as well as their 11 291 target genes, and 17 909 simple sequence repeats (SSRs) were identified. The data also revealed 97 candidate transcripts related to asarinin metabolism, of which six novel genes that encoded enzymes involved in asarinin biosynthesis were initially reported. In addition, 56 transcripts related to aristolochic acid biosynthesis were also identified, including CYP81B. In summary, these transcriptome data provide a useful resource to study gene function and genetic engineering in A. sieboldii.

Characterisation, expression and functional analysis of PAL gene family in Cephalotaxus hainanensis

Phenylalanine ammonia lyase (PAL) is the first committed step in the formation of phenylpropanoids, and catalyses the deamination of L-phenylalanine (L-Phe) to yield cinnamic acid. While PALs are common in plants, PAL genes involved in alkaloid biosynthesis in Cephalotaxus hainanensis have never been described. To obtain better knowledge of PAL genes and their number and function involved in Cephalotaxus alkaloid biosynthesis four PAL genes were screened and cloned. In vitro enzymatic analysis showed that all four PAL recombinant proteins could convert L-Phe to product trans-cinnamic acid, and showed strict substrate specificity. Moreover, the expression profiles of four ChPALs were analysed using qRT-PCR, which showed that they had higher transcript levels in roots and stems, and that different ChPALs displayed different response sensitivities and change patterns in response to stimuli. Several metabolic compounds were measured in stimulated leaves using UPLC-MS, and indicating the concentration of Cephalotaxus alkaloids and cinnamic acid in leaves subjected to different conditions. These concentrations increased significantly after treatment with 100 mM NaCl, 100 mM mannitol, 100 μM SA and 10 μM ABA. The expression levels of four PAL genes showed indications of upregulation after treatment. These results supply an important foundation for further research on candidate genes involved in the biosynthesis of Cephalotaxus alkaloids.

Functional characterization of cinnamate 4-hydroxylase from Helianthus annuus Linn using a fusion protein method

Sunflower (Helianthus annuus L.) is an important oil crop, the secondary metabolites of it include many compounds such as flavonoids and lignin. However, the research on the biosynthesis of phenolic compounds in sunflowers is still scarce. Cinnamate 4-hydroxylase (C4H) belongs to the cytochrome P450-dependent monooxygenase family and is involved in the synthesis of many phenolic compounds, but C4H in sunflowers has not yet been cloned and functionally characterized. In this study, we screened three C4H genes from the sunflower transcriptome and genomic databases, named HaC4H1, HaC4H2, and, HaC4H3, respectively. In heterologous expression experiments, we had improved a method from previous studies by the addition of restriction sites to make it easier to express multiple C4H functions and suitable for in vitro activity verification. HaC4Hs without the N-terminal membrane anchor region was fused with a redox partner of Arabidopsis thaliana cytochrome P450 enzyme (CYP450) by the method and functionally expressed in E. coli and the results showed that these three enzymes catalyzed the formation of p-coumaric acid. To further investigate whether our fusion protein approach is applicable to other C4Hs, we used this method to explore the functions of C4H from Peucedanum praeruptorum and Angelica decursiva, and they can also convert trans-cinnamic acid to p-coumaric acid. The gene expression profile showed that all three HaC4H genes showed the highest transcription levels in the roots and might be up-regulated by MeJA. In summary, these results reveal the function of HaC4Hs in sunflower and provide a simpler way to explore C4H and even other cytochrome P450 enzymes in prokaryotic expression systems.

Purification and Characterization of Anabaena flos-aquae Phenylalanine Ammonia-Lyase as a Novel Approach for Myristicin Biotransformation

Phenylalanine ammonia-lyase (PAL) catalyzes the reversible deamination of phenylalanine to cinnamic acid and ammonia. Algae have been considered as biofactories for PAL production, however, biochemical characterization of PAL and its potency for myristicin biotransformation into MMDA (3-methoxy-4, 5-methylenedioxyamphetamine) has not been studied yet. Thus, PAL from Anabaena flos-aquae and Spirulina platensis has been purified, comparatively characterized and its affinity to transform myristicin was assessed. The specific activity of purified PAL from S. platensis (73.9 μmol/mg/min) and A. flos-aquae (30.5 μmol/mg/min) was increased by about 2.9 and 2.4 folds by gel-filtration comparing to their corresponding crude enzymes. Under denaturing-PAGE, a single proteineous band with a molecular mass of 64 kDa appeared for A. flos-aquae and S. platensis PAL. The biochemical properties of the purified PAL from both algal isolates were determined comparatively. The optimum temperature of S. platensis and A. flos-aquae PAL for forward or reverse activity was reported at 30°C, while the optimum pH for PAL enzyme isolated from A. flos-aquae was 8.9 for forward and reverse activities, and S. platensis PAL had maximum activities at pH 8.9 and 8 for forward and reverse reactions, respectively. Luckily, the purified PALs have the affinity to hydroaminate the myristicin to MMDA successfully in one step. Furthermore, a successful method for synthesis of MMDA from myristicin in two steps was also established. Gas chromatography-mass spectrometry (GC-MS) analysis was conducted to track the product formation.

Functional characterization and correlation analysis of phenylalanine ammonia-lyase (PAL) in coumarin biosynthesis from Peucedanum praeruptorum Dunn

Coumarins exhibit many biological activities and are the main specialised metabolites of Peucedanum praeruptorum Dunn, an important plant used in traditional Chinese medicine. In preliminary studies, we cloned several genes involved in coumarin biosynthesis in P. praeruptorum, such as 4-coumarate: CoA ligase (4CL), p-coumaroyl CoA 2'-hydroxylase (C2'H), feruloyl CoA 6'-hydroxylase (F6'H) and bergaptol O-methyltransferase (BMT). However, phenylalanine ammonia-lyase (PAL) in P. praeruptorum (PpPAL) has not yet been studied. In the present study, we cloned one novel PpPAL gene. Subsequently, the relationship between gene and compounds was studied using quantitative real-time PCR (qRT-PCR) and High Performance Liquid Chromatography (HPLC) analysis. Then, enzyme function was analyzed with _L-phenylalanine (_L-Phe) as substrate. These experiments showed that the coumarin content could be upregulated by methyl jasmonate (MeJA), UV irradiation and cold, which was consistent with increased expression levels of PpPAL. In addition, correlation analysis indicated that coumarins were partially related to PpPAL. And the recombinant protein could catalyze the conversion of _L-Phe to trans-cinnamic acid (t-CA) with a K_m of 120 ± 33 μM and a K_cat of 117 ± 32 min^-1. Besides, Tyr110, Phe116, Gly117, Ser206, Leu209, Leu259, Tyr354, Arg357, Asn387 and Phe403 were essential for enzymatic activity based on three-dimensional modeling and site-directed mutagenesis experiments. Altogether these results highlight the importance of PpPAL in abiotically induced coumarin biosynthesis and provide further insights regarding the structure-function relationships of this protein.

Investigation of the dynamic changes in the chemical constituents of Chinese “Laba” garlic during traditional processing

In this study, the whole chemical constituents influencing colour, flavor and physiological function of “Laba” garlic during traditional processing have been investigated.

Expression of Genes Related to Phenylpropanoid Biosynthesis in Different Organs of Ixeris dentata var. albiflora

Members of the genus Ixeris have long been used in traditional medicines as stomachics, sedatives, and diuretics. Phenylalanine ammonia-lyase (PAL), cinnamate-4-hydroxylase (C4H), 4-coumarate: coenzyme-A (CoA) ligase (4CL), chalcone synthase (CHS), and dihydroflavonol 4-reductase (DFR) are important enzymes in the phenylpropanoid pathway. In this study, we analyzed seven genes from Ixeris dentata var. albiflora that are involved in phenylpropanoid biosynthesis, using an Illumina/Solexa HiSeq 2000 platform. The amino acid sequence alignments for IdPALs, IdC4H, Id4CLs, IdCHS, and IdDFR showed high identity to sequences from other plants. We also investigated transcript levels using quantitative real-time PCR, and analyzed the accumulation of phenylpropanoids in different organs of I. dentata var. albiflora using high-performance liquid chromatography. The transcript levels of IdC4H, Id4CL1, IdCHS, and IdDFR were highest in the leaf. The catechin, chlorogenic acid, ferulic acid, and quercetin contents were also highest in the leaf. We suggest that expression of IdC4H, Id4CL1, IdCHS, and IdDFR is associated with the accumulation of phenylpropanoids. Our results may provide baseline information for elucidating the mechanism of phenylpropanoid biosynthesis in different organs of I. dentata var. albiflora.

Accumulation of Rutin and Betulinic Acid and Expression of Phenylpropanoid and Triterpenoid Biosynthetic Genes in Mulberry (Morus alba L.)

Mulberry (Morus alba L.) is used in traditional Chinese medicine and is the sole food source of the silkworm. Here, 21 cDNAs encoding phenylpropanoid biosynthetic genes and 21 cDNAs encoding triterpene biosynthetic genes were isolated from mulberry. The expression levels of genes involved in these biosynthetic pathways and the accumulation of rutin, betulin, and betulinic acid, important secondary metabolites, were investigated in different plant organs. Most phenylpropanoid and triterpene biosynthetic genes were highly expressed in leaves and/or fruit, and most genes were downregulated during fruit ripening. The accumulation of rutin was more than fivefold higher in leaves than in other organs, and higher levels of betulin and betulinic acid were found in roots and leaves than in fruit. By comparing the contents of these compounds with gene expression levels, we speculate that MaUGT78D1 and MaLUS play important regulatory roles in the rutin and betulin biosynthetic pathways.

Ultraviolet Radiation-Elicited Enhancement of Isoflavonoid Accumulation, Biosynthetic Gene Expression, and Antioxidant Activity in Astragalus membranaceus Hairy Root Cultures

In this work, Astragalus membranaceus hairy root cultures (AMHRCs) were exposed to ultraviolet radiation (UV-A, UV-B, and UV-C) for promoting isoflavonoid accumulation. The optimum enhancement for isoflavonoid production was achieved in 34-day-old AMHRCs elicited by 86.4 kJ/m(2) of UV-B. The resulting isoflavonoid yield was 533.54 ± 13.61 μg/g dry weight (DW), which was 2.29-fold higher relative to control (232.93 ± 3.08 μg/g DW). UV-B up-regulated the transcriptional expressions of all investigated genes involved in isoflavonoid biosynthetic pathway. PAL and C4H were found to be two potential key genes that controlled isoflavonoid biosynthesis. Moreover, a significant increase was noted in antioxidant activity of extracts from UV-B-elicited AMHRCs (IC50 values = 0.85 and 1.08 mg/mL) in comparison with control (1.38 and 1.71 mg/mL). Overall, this study offered a feasible elicitation strategy to enhance isoflavonoid accumulation in AMHRCs and also provided a basis for metabolic engineering of isoflavonoid biosynthesis in the future.

Accumulation of kaempferitrin and expression of phenyl-propanoid biosynthetic genes in kenaf (Hibiscus cannabinus)

Kenaf (Hibiscus cannabinus) is cultivated worldwide for its fiber; however, the medicinal properties of this plant are currently attracting increasing attention. In this study, we investigated the expression levels of genes involved in the biosynthesis of kaempferitrin, a compound with many biological functions, in different kenaf organs. We found that phenylalanine ammonia lyase (HcPAL) was more highly expressed in stems than in other organs. Expression levels of cinnamate 4-hydroxylase (HcC4H) and 4-coumarate-CoA ligase (Hc4CL) were highest in mature leaves, followed by stems and young leaves, and lowest in roots and mature flowers. The expression of chalcone synthase (HcCHS), chalcone isomerase (HcCHI), and flavone 3-hydroxylase (HcF3H) was highest in young flowers, whereas that of flavone synthase (HcFLS) was highest in leaves. An analysis of kaempferitrin accumulation in the different organs of kenaf revealed that the accumulation of this compound was considerably higher (>10-fold) in leaves than in other organs. On the basis of a comparison of kaempferitrin contents with the expression levels of different genes in different organs, we speculate that HcFLS plays an important regulatory role in the kaempferitrin biosynthetic pathway in kenaf.

Differential inductions of phenylalanine ammonia-lyase and chalcone synthase during wounding, salicylic acid treatment, and salinity stress in safflower, Carthamus tinctorius

Safflower (Carthamus tinctorius L.) serves as a reference dicot for investigation of defence mechanisms in Asteraceae due to abundant secondary metabolites and high resistance/tolerance to environmental stresses. In plants, phenylpropanoid and flavonoid pathways are considered as two central defence signalling cascades in stress conditions. Here, we describe the isolation of two major genes in these pathways, CtPAL (phenylalanine ammonia-lyase) and CtCHS (chalcone synthase) in safflower along with monitoring their expression profiles in different stress circumstances. The aa (amino acid) sequence of isolated region of CtPAL possesses the maximum identity up to 96% to its orthologue in Cynara scolymus, while that of CtCHS retains the highest identity to its orthologue in Callistephus chinensis up to 96%. Experiments for gene expression profiling of CtPAL and CtCHS were performed after the treatment of seedlings with 0.1 and 1 mM SA (salicylic acid), wounding and salinity stress. The results of semi-quantitative RT–PCR revealed that both CtPAL and CtCHS genes are further responsive to higher concentration of SA with dissimilar patterns. Regarding wounding stress, CtPAL gets slightly induced upon injury at 3 hat (hours after treatment) (hat), whereas CtCHS gets greatly induced at 3 hat and levels off gradually afterward. Upon salinity stress, CtPAL displays a similar expression pattern by getting slightly induced at 3 hat, but CtCHS exhibits a biphasic expression profile with two prominent peaks at 3 and 24 hat. These results substantiate the involvement of phenylpropanoid and particularly flavonoid pathways in safflower during wounding and especially salinity stress.

Overexpression of Cinnamate 4-Hydroxylase and 4-Coumaroyl CoA Ligase Prompted Flavone Accumulation inScutellaria baicalensisHairy Roots

Scutellaria baicalensis Georgi, a species of the Lamiaceae family, is considered as one of the 50 fundamental herbs used in traditional Chinese medicine. In order to enhance flavone (baicalein, baicalin, and wogonin) content in S. baicalensis roots, we overexpressed a single gene of cinnamate 4-hydroxylase (C4H) and 4-coumaroyl coenzyme A ligase (4CL) using an Agrobacterium rhizogenes-mediated system. SbC4H- and Sb4CL-overexpressed hairy root lines enhanced the transcript levels of SbC4H and Sb4CL compared with those in the control and also increased flavones contents by approximately 3- and 2.5-fold, respectively. We successfully engineered the flavone biosynthesis pathway for the production of beneficial flavones in S. baicalensis hairy roots. The importance of upstream gene C4H and 4CL in flavone biosynthesis and the efficiency of metabolic engineering in promoting flavone biosynthesis in S. baicalensis hairy roots have been indicated in this study.

Molecular cloning and characterization of genes involved in rosmarinic acid biosynthesis from Prunella vulgaris

Prunella vulgaris L., commonly known as "self-heal" or "heal-all," is a perennial herb with a long history of medicinal use. Phenylalanine ammonia-lyase (PAL), cinnamate 4-hydroxylase (C4H), and 4-coumarate:coenzyme-A (CoA) ligase (4CL) are important enzymes in the phenylpropanoid pathway and in the accumulation of rosmarinic acid (RA), which is a major secondary metabolite in P. vulgaris. In this study, we isolated cDNAs encoding PvPAL, PvC4H, and Pv4CL from P. vulgaris using rapid amplification of cDNA ends polymerase chain reaction (PCR). The amino acid sequence alignments of PvPAL, PvC4H, and Pv4CL showed high sequence identity to those of other plants. Quantitative real-time PCR analysis was used to determine the transcript levels of genes involved in RA biosynthesis in the flowers, leaves, stems, and roots of P. vulgaris. The transcript levels of PvPAL, PvC4H, and Pv4CL1 were the highest in flowers, whereas Pv4CL2 was the highest in roots. High-performance liquid chromatography analysis also showed the highest RA content in the flowers (3.71 mg/g dry weight). We suggest that the expression of the PvPAL, PvC4H, and Pv4CL1 genes is correlated with the accumulation of RA. Our results revealed that P. vulgaris flowers are appropriate for medicinal usage, and our findings provide support for increasing RA production in this plant.

Identification of phenylpropanoid biosynthetic genes and phenylpropanoid accumulation by transcriptome analysis of Lycium chinense

Background

Lycium chinense is well known in traditional Chinese herbal medicine for its medicinal value and composition, which have been widely studied for decades. However, further research on Lycium chinense is limited due to the lack of transcriptome and genomic information.

Results

The transcriptome of L. chinense was constructed by using an Illumina HiSeq 2000 sequencing platform. All 56,526 unigenes with an average length of 611 nt and an N50 equaling 848 nt were generated from 58,192,350 total raw reads after filtering and assembly. Unigenes were assembled by BLAST similarity searches and annotated with Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) orthology identifiers. Using these transcriptome data, the majority of genes that are associated with phenylpropanoid biosynthesis in L. chinense were identified. In addition, phenylpropanoid biosynthesis-related gene expression and compound content in different organs were analyzed. We found that most phenylpropanoid genes were highly expressed in the red fruits, leaves, and flowers. An important phenylpropanoid, chlorogenic acid, was also found to be extremely abundant in leaves.

Conclusions

Using Illumina sequencing technology, we have identified the function of novel homologous genes that regulate metabolic pathways in Lycium chinense.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-14-802) contains supplementary material, which is available to authorized users.

Low-temperature conditioning of "seed" cloves enhances the expression of phenolic metabolism related genes and anthocyanin content in 'Coreano' garlic (Allium sativum) during plant development

Low-temperature conditioning of garlic "seed" cloves accelerated the development of the crop cycle, decreased plant growth, and increased the synthesis of phenolic compounds and anthocyanins in the outer scale leaves of the bulbs at harvest time, leading to 3-fold content increase compared with those conditioned at room temperature. Cold conditioning of "seed" cloves also altered the anthocyanin profile during bulb development and at harvest. Two new anthocyanins are reported for the first time in garlic. The high phenolics and anthocyanin contents in bulbs of plants generated from "seed" cloves conditioned at 5 °C for 5 weeks were preceded by overexpression of some putative genes of the phenolic metabolism [6-fold for phenylalanine ammonia lyase (PAL)] and anthocyanin synthesis [1-fold for UDP-sugar:flavonoid 3-O-glycosyltransferase (UFGT)] compared with those conditioned at room temperature.

Cloning and characterisation of a phenylalanine ammonia-lyase gene from Rhus chinensis

The gene and cDNA sequence encoding PAL from Chinese medicinal plant Rhus chinensis were cloned and analyzed, furthermore the biochemical properties, kinetic parameters, differential expression and key sites were studied. Rhus chinensis is a well-known Chinese medicinal plant. Phenylalanine ammonia-lyase (PAL) is the first enzyme of phenylpropanoid pathway. Several recent studies suggested that PAL also play an important role in plant-aphid interaction. In this study, both the cDNA and the genomic sequence encoding PAL from Rhus chinensis (designated as RcPAL) were cloned and analyzed. The 3,833 bp gene contained a 1,342 bp intron and two extrons. The ORF was 2,124 bp and predicted to encode a 707-amino acid polypeptide. The results of real-time PCR showed that RcPAL expressed in all tested tissues and followed the order: stems > young leaves > petioles > roots > seeds > mature leaves. RcPAL was successfully expressed in E. coli with the pET-28a-RcPAL recombinant vector. The recombinant protein exhibited a high level of PAL activity. Biochemical properties and kinetic parameters of recombinant RcPAL were further studied. The results showed that the optimal temperature and pH for RcPAL activity were 45 °C and 9.0, and the K m and K cat values were 7.90 mM and 52.31 s(-1), respectively. The active sites and substrate selectivity site were also investigated with site-directed mutagenesis methods, suggesting that Phe(126) is responsible for the substrate selectivity. To our knowledge, this was the first full-length PAL gene cloned and characterized from the family Anacardiaceae so far.

Carotenoid content and expression of phytoene synthase and phytoene desaturase genes in bitter melon (Momordica charantia)

Momordica charantia, a tropical plant, produces a fruit that has a β-carotene concentration five times higher than that of carrot. To elucidate the molecular basis of β-carotene accumulation in M. charantia, the gene expression levels of phytoene synthase (McPSY) and phytoene desaturase (McPDS) were determined. These levels were particularly high in the flowers of M. charantia. During fruit maturation, the expression levels of McPSY and McPDS decreased during the mid-stages but increased in the fully mature fruit. In addition, carotenoids accumulated as the peel changed from green to orange. Thus, McPSY and McPDS expression correlated with carotenoid accumulation during fruit maturation. Principal component analysis (PCA) also was used to evaluate the differences among the profiles of seven carotenoids identified in the fruit at several maturation stages. Riper fruits had higher carotenoid concentrations than less ripe fruits.