Correction: Sundaraj et al. Cloning, Expression and Functional Characterization of a Novel α-Humulene Synthase, Responsible for the Formation of Sesquiterpene in Agarwood Originating from Aquilaria malaccensis. Curr. Issues Mol. Biol. 2023, 45, 8989-9002.

Afiq Adham Abd Rasib and Roohaida Othman were not included as authors in the original publication [...].

Functional characterization of sesquiterpene synthase from Polygonum minus.

Polygonum minus is an aromatic plant, which contains high abundance of terpenoids, especially the sesquiterpenes C15H24. Sesquiterpenes were believed to contribute to the many useful biological properties in plants. This study aimed to functionally characterize a full length sesquiterpene synthase gene from P. minus. P. minus sesquiterpene synthase (PmSTS) has a complete open reading frame (ORF) of 1689 base pairs encoding a 562 amino acid protein. Similar to other sesquiterpene synthases, PmSTS has two large domains: the N-terminal domain and the C-terminal metal-binding domain. It also consists of three conserved motifs: the DDXXD, NSE/DTE, and RXR. A three-dimensional protein model for PmSTS built clearly distinguished the two main domains, where conserved motifs were highlighted. We also constructed a phylogenetic tree, which showed that PmSTS belongs to the angiosperm sesquiterpene synthase subfamily Tps-a. To examine the function of PmSTS, we expressed this gene in Arabidopsis thaliana. Two transgenic lines, designated as OE3 and OE7, were further characterized, both molecularly and functionally. The transgenic plants demonstrated smaller basal rosette leaves, shorter and fewer flowering stems, and fewer seeds compared to wild type plants. Gas chromatography-mass spectrometry analysis of the transgenic plants showed that PmSTS was responsible for the production of ß -sesquiphellandrene.

Monoterpene alcohol metabolism: identification, purification, and characterization of two geraniol dehydrogenase isoenzymes from Polygonum minus leaves.

NADP(+)-dependent geraniol dehydrogenase (EC 1.1.1.183) is an enzyme that catalyzes the oxidation of geraniol to geranial. Stable, highly active cell-free extract was obtained from Polygonum minus leaves using polyvinylpolypyrrolidone, Amberlite XAD-4, glycerol, 2-mercaptoethanol, thiourea, and phenylmethylsulfonylfluoride in tricine-NaOH buffer (pH 7.5). The enzyme preparation was separated into two activity peaks, geraniol-DH I and II, by DEAE-Toyopearl 650M column chromatography at pH 7.5. Both isoenzymes were purified to homogeneity in three chromatographic steps. The geraniol-DH isoenzymes were similar in molecular mass, optimal temperature, and pH, but the isoelectric point, substrate specificity, and kinetic parameters were different. The K(m) values for geraniol of geraniol-DH I and II appeared to be 0.4 mM and 0.185 mM respectively. P. minus geraniol-DHs are unusual among geraniol-DHs in view of their thermal stability and optimal temperatures, and also their high specificity for allylic alcohols and NADP(+).

Flavonoid biosynthesis genes putatively identified in the aromatic plant Polygonum minus via Expressed Sequences Tag (EST) analysis.

P. minus is an aromatic plant, the leaf of which is widely used as a food additive and in the perfume industry. The leaf also accumulates secondary metabolites that act as active ingredients such as flavonoid. Due to limited genomic and transcriptomic data, the biosynthetic pathway of flavonoids is currently unclear. Identification of candidate genes involved in the flavonoid biosynthetic pathway will significantly contribute to understanding the biosynthesis of active compounds. We have constructed a standard cDNA library from P. minus leaves, and two normalized full-length enriched cDNA libraries were constructed from stem and root organs in order to create a gene resource for the biosynthesis of secondary metabolites, especially flavonoid biosynthesis. Thus, large-scale sequencing of P. minus cDNA libraries identified 4196 expressed sequences tags (ESTs) which were deposited in dbEST in the National Center of Biotechnology Information (NCBI). From the three constructed cDNA libraries, 11 ESTs encoding seven genes were mapped to the flavonoid biosynthetic pathway. Finally, three flavonoid biosynthetic pathway-related ESTs chalcone synthase, CHS (JG745304), flavonol synthase, FLS (JG705819) and leucoanthocyanidin dioxygenase, LDOX (JG745247) were selected for further examination by quantitative RT-PCR (qRT-PCR) in different P. minus organs. Expression was detected in leaf, stem and root. Gene expression studies have been initiated in order to better understand the underlying physiological processes.

Transcriptome of Aquilaria malaccensis containing agarwood formed naturally and induced artificially.

OBJECTIVES: Agarwood is the aromatic heartwood formed upon wounding of Aquilaria trees either naturally formed due to physical wound sustained from natural phenomena followed by microbial infection, or artificially induced using different inoculation methods. Different induction methods produce agarwoods with different aromas which have impacts on their commercial values. In lieu of elucidating the molecular mechanisms of agarwood formation under different treatment conditions, the transcriptome profiles of trunk tissues from healthy A. malaccensis tree, and naturally and artificially induced trees were obtained. DATA DESCRIPTION: The transcriptome of trunk tissues from healthy A. malaccensis, and naturally and artificially induced trees were sequenced using Illumina HiSeq™ 4000 platform which resulted in a total of 38.4 Gb clean reads with Q30 rate of at least 91%. The transcriptome consists of 85,986 unigenes containing 1305 bases on average which were annotated against several databases. From this, 44,654 unigenes were mapped to 290 metabolic pathways in the Kyoto Encyclopedia of Genes and Genomes database. These transcriptome data represent considerable contribution towards Aquilaria transcriptome data and enhance current knowledge in comprehending the molecular mechanisms underlying agarwood formation in Aquilaria spp.

Datasets of essential oils from naturally formed and synthetically induced Aquilaria malaccensis agarwoods.

Agarwood is the highly valuable fragrant resin of the wounded Aquilaria spp. trees widely used in fragrances, medicines and incenses. Among the Aquilaria spp., A. malaccensis is the primary producer and is mainly found in Indonesia and Malaysia. In normal condition, agarwood is naturally formed in Aquilaria trees as a defense mechanism upon physical damage or microbial infection on the trees, which is a slow process that occurs over several years. The high demand in agarwood has spurred the development of various artificial inoculation methods where agarwood formation is synthetically induced in a shorter period of time. However, the synthetic induction method produces agarwood with aromas different from the naturally formed agarwood. To understand the changes in the agarwoods produced from different induction conditions, metabolite profiling of agarwood essential oil from A. malaccensis has been performed. The essential oils of healthy undamaged tree trunks and, naturally formed and synthetically induced agarwoods were obtained using hydrodistillation (HS) method and analysed using gas chromatography mass spectrometer (GC-MS). These data will provide valuable resources for chemical components of agarwood produced by the species in the genus Aquilaria.

Site-directed mutagenesis of ß sesquiphellandrene synthase enhances enzyme promiscuity.

The chemical formation of terpenes in nature is carried out by terpene synthases as the main biocatalysts to guide the carbocation intermediate to form structurally diverse compounds including acyclic, mono- and multiple cyclic products. Despite intensive study of the enzyme active site, the mechanism of specific terpene biosynthesis remains unclear. Here we demonstrate that a single mutation of the amino acid L454G or L454A in the active site of Persicaria minor ß-sesquiphellandrene synthase leads to a more promiscuous enzyme that is capable of producing additional hydroxylated sesquiterpenes such as sesquicineole, sesquisabinene hydrate and α-bisabolol. Furthermore, the same L454 residue mutation (L454G or L454A) in the active site also improves the protein homogeneity compared to the wild type protein. Taken together, our results demonstrate that residue Leucine 454 in the active site of ß-sesquiphellandrene synthase is important for sesquiterpene product diversity as well as the protein homogeneity in solution.

Transcriptome data of the carrageenophyte Eucheuma denticulatum.

Eucheuma denticulatum or commonly known as "Spinosum", is an economically important red alga that naturally grows on coral reefs with moderately strong currents in tropical and sub-tropical areas. This species is the primary source of iota-carrageenan which has high demands in the food, pharmaceutical and manufacturing industries, and as such it has been widely cultivated. The increasing global demand for carrageenan has led to extensive commercial cultivation of carrageenophytes mainly in the tropics. The carrageenophyte seaweeds including E. denticulatum are indigenous to Sabah, Malaysia. To enrich the information on the genes involved in carrageenan biosynthesis, RNA sequencing has been performed and transcriptomic dataset has been generated using Illumina HiSeq™ 2000 sequencer. The raw data and transcriptomic data have been deposited in NCBI database with the accession number PRJNA477734. These data will provide valuable resources for functional genomics annotation and investigation of mechanisms underlying the regulations of genes in this algal species.

Purification and biochemical characterization of recombinant Persicaria minor ß-sesquiphellandrene synthase.

BACKGROUND: Sesquiterpenes are 15-carbon terpenes synthesized by sesquiterpene synthases using farnesyl diphosphate (FPP) as a substrate. Recently, a sesquiterpene synthase gene that encodes a 65 kDa protein was isolated from the aromatic plant Persicaria minor. Here, we report the expression, purification and characterization of recombinant P. minor sesquiterpene synthase protein (PmSTS). Insights into the catalytic active site were further provided by structural analysis guided by multiple sequence alignment. METHODS: The enzyme was purified in two steps using affinity and size exclusion chromatography. Enzyme assays were performed using the malachite green assay and enzymatic product was identified using gas chromatography-mass spectrometry (GC-MS) analysis. Sequence analysis of PmSTS was performed using multiple sequence alignment (MSA) against plant sesquiterpene synthase sequences. The homology model of PmSTS was generated using I-TASSER server. RESULTS: Our findings suggest that the recombinant PmSTS is mainly expressed as inclusion bodies and soluble aggregate in the E. coli protein expression system. However, the addition of 15% (v/v) glycerol to the protein purification buffer and the removal of N-terminal 24 amino acids of PmSTS helped to produce homogenous recombinant protein. Enzyme assay showed that recombinant PmSTS is active and specific to the C15 substrate FPP. The optimal temperature and pH for the recombinant PmSTS are 30 °C and pH 8.0, respectively. The GC-MS analysis further showed that PmSTS produces ß-sesquiphellandrene as a major product and ß-farnesene as a minor product. MSA analysis revealed that PmSTS adopts a modified conserved metal binding motif (NSE/DTE motif). Structural analysis suggests that PmSTS may binds to its substrate similarly to other plant sesquiterpene synthases. DISCUSSION: The study has revealed that homogenous PmSTS protein can be obtained with the addition of glycerol in the protein buffer. The N-terminal truncation dramatically improved the homogeneity of PmSTS during protein purification, suggesting that the disordered N-terminal region may have caused the formation of soluble aggregate. We further show that the removal of the N-terminus disordered region of PmSTS does not affect the product specificity. The optimal temperature, optimal pH, Km and kcat values of PmSTS suggests that PmSTS shares similar enzyme characteristics with other plant sesquiterpene synthases. The discovery of an altered conserved metal binding motif in PmSTS through MSA analysis shows that the NSE/DTE motif commonly found in terpene synthases is able to accommodate certain level of plasticity to accept variant amino acids. Finally, the homology structure of PmSTS that allows good fitting of substrate analog into the catalytic active site suggests that PmSTS may adopt a sesquiterpene biosynthesis mechanism similar to other plant sesquiterpene synthases.

Purification and properties of a beta-galactosidase from carambola fruit with significant activity towards cell wall polysaccharides.

beta-Galactosidase (EC. 3.2.1.23) from ripe carambola (Averrhoa carambola L. cv. B10) fruit was fractionated through a combination of ion exchange and gel filtration chromatography into four isoforms, viz. beta-galactosidase I, II, III and IV. This beta-galactosidases had apparent native molecular masses of 84, 77, 58 and 130 kDa, respectively. beta-Galactosidase I, the predominant isoform, was purified to electrophoretic homogeneity; analysis of the protein by SDS-PAGE revealed two subunits with molecular masses of 48 and 36 kDa. N-terminal amino acid sequence of the respective polypeptides shared high similarities albeit at different domains, with the deduced amino acid sequence of certain plant beta-galactosidases, thus, explaining the observed low similarity between the two subunits. beta-Galactosidase I was probably a heterodimer that have glycoprotein properties and a pI value of 7.2, with one of the potential glycosylation sites appeared to reside within the 48-kDa-polypeptide. The purified beta-galactosidase I was substantially active in hydrolyzing (1-->4)beta-linked spruce and a mixture of (1-->3)beta- and (1-->6)beta-linked gum arabic galactans. This isoform also had the capability to solubilize and depolymerize structurally intact pectins as well as to modify alkaline-soluble hemicelluloses, reflecting in part changes that occur during ripening.

Engineering the lactococcal mevalonate pathway for increased sesquiterpene production.

Isoprenoids are a large, diverse group of secondary metabolites which has recently raised a renewed research interest due to genetic engineering advances, allowing specific isoprenoids to be produced and characterized in heterologous hosts. Many researches on metabolic engineering of heterologous hosts for increased isoprenoid production are focussed on Escherichia coli and yeasts. E. coli, as most prokaryotes, use the 2-C-methyl-d-erythritol-4-phosphate (MEP) pathway for isoprenoid production. Yeasts on the other hand, use the mevalonate pathway which is commonly found in eukaryotes. However, Lactococcus lactis is an attractive alternative host for heterologous isoprenoid production. Apart from being food-grade, this Gram-positive prokaryote uses the mevalonate pathway for isoprenoid production instead of the MEP pathway. Previous studies have shown that L. lactis is able to produce sesquiterpenes through heterologous expression of plant sesquiterpene synthases. In this work, we analysed the gene expression of the lactococcal mevalonate pathway through RT-qPCR to successfully engineer L. lactis as an efficient host for isoprenoid production. We then overexpressed the mvk gene singly or co-expressed with the mvaA gene as an attempt to increase ß-sesquiphellandrene production in L. lactis. It was observed that co-expression of mvk with mvaA doubled the amount of ß-sesquiphellandrene produced.

Overexpressing 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) in the lactococcal mevalonate pathway for heterologous plant sesquiterpene production.

Isoprenoids are a large and diverse group of metabolites with interesting properties such as flavour, fragrance and therapeutic properties. They are produced via two pathways, the mevalonate pathway or the 2-C-methyl-D-erythritol-4-phosphate (MEP) pathway. While plants are the richest source of isoprenoids, they are not the most efficient producers. Escherichia coli and yeasts have been extensively studied as heterologous hosts for plant isoprenoids production. In the current study, we describe the usage of the food grade Lactococcus lactis as a potential heterologous host for the production of sesquiterpenes from a local herbaceous Malaysian plant, Persicaria minor (synonym Polygonum minus). A sesquiterpene synthase gene from P. minor was successfully cloned and expressed in L. lactis. The expressed protein was identified to be a ß-sesquiphellandrene synthase as it was demonstrated to be functional in producing ß-sesquiphellandrene at 85.4% of the total sesquiterpenes produced based on in vitro enzymatic assays. The recombinant L. lactis strain developed in this study was also capable of producing ß-sesquiphellandrene in vivo without exogenous substrates supplementation. In addition, overexpression of the strain's endogenous 3-hydroxy-3-methylglutaryl coenzyme-A reductase (HMGR), an established rate-limiting enzyme in the eukaryotic mevalonate pathway, increased the production level of ß-sesquiphellandrene by 1.25-1.60 fold. The highest amount achieved was 33 nM at 2 h post-induction.

EuDBase: An online resource for automated EST analysis pipeline (ESTFrontier) and database for red seaweed Eucheuma denticulatum.

Functional genomics has proven to be an efficient tool in identifying genes involved in various biological functions. However the availability of commercially important seaweed Eucheuma denticulatum functional resources is still limited. EuDBase is the first seaweed online repository that provides integrated access to ESTs of Eucheuma denticulatum generated from samples collected from Kudat and Semporna in Sabah, Malaysia. The database stored 10,031 ESTs that are clustered and assembled into 2,275 unique transcripts (UT) and 955 singletons. Raw data were automatically processed using ESTFrontier, an in-house automated EST analysis pipeline. Data was collected in MySQL database. Web interface is implemented using PHP and it allows browsing and querying EuDBase through search engine. Data is searchable via BLAST hit, domain search, Gene Ontology or KEGG Pathway. A user-friendly interface allows the identification of sequences either using a simple text query or similarity search. The development of EuDBase is initiated to store, manage and analyze the E. denticulatum ESTs and to provide accumulative digital resources for the use of global scientific community. EuDBase is freely available from http://www.inbiosis.ukm.my/eudbase/.

Fruit-specific expression of papaya subtilase gene.

Subtilisin-like serine proteases (EC 3.4.21) consist of a widespread family of enzymes that is involved in various processes including in plants. The full-length cDNA (CpSUB1) and the corresponding genomic DNA for papaya subtilase have been obtained using rapid amplification of cDNA ends (RACEs) and PCR primer walking techniques, respectively. The cDNA clone contains an open reading frame of 2316bp encoding 772 amino acids with a calculated molecular mass of 82.6kDa and an isoelectric point (pI) of 8.97. The CpSUB1 gene is composed of nine exons and eight introns. The amino acid sequence encoded by CpSUB1 shared high identity (>60%) with the amino acid sequence of other plant subtilisin-like proteases. Sequence analysis of CpSUB1 revealed the presence of a possible signal peptide (25 amino acid residues) and an NH(2)-terminal prosequence (88 amino acid residues). In addition, papaya subtilase possesses the characteristic subtilisin catalytic triad amino acids namely Asp, His and Ser, together with the substrate-binding site, Asn. DNA hybridization analysis showed that subtilase gene exists as a single copy in the papaya genome. RNA hybridization analyses showed that expression of the subtilase transcripts was only detected in mesocarp but not in non-fruit tissues. Gene expression in fruit tissues reached the highest level during the ripening stage at which the fruits undergo dramatic softening process. Subsequently, pro-subtilase ( approximately 80kDa) was expressed as recombinant pro-enzyme ( approximately 97kDa), which was used to generate antiserum against papaya subtilase, anti-sub. Protein gel blot analysis using anti-sub towards total protein extracted from all ripening stages revealed that a protein with a molecular mass of approximately 70kDa reacted with the antiserum. Hence both RNA hybridization and protein gel blot analyses confirmed the presence of subtilase during papaya fruit ripening, pointing to its possible involvement in this important process.