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Maize is often subjected to various environmental stresses. The strictosidine synthase-like (SSL) family is thought to catalyze the key step in the monoterpene alkaloids synthesis pathway in response to environmental stresses. However, the role of ZmSSL genes in maize growth and development and its response to stresses is unknown. Herein, we undertook the systematic identification and analysis of maize SSL genes. Twenty SSL genes were identified in the maize genome. Except for chromosomes 3, 5, 6, and 10, they were unevenly distributed on the remaining 6 chromosomes. A total of 105 SSL genes from maize, sorghum, rice, Aegilops tauschii, and Arabidopsis were divided into five evolutionary groups, and ZmSSL gene structures and conserved protein motifs in the same group were similar. A collinearity analysis showed that tandem duplication plays an important role in the evolution of the SSL family in maize, and ZmSSL genes share more collinear genes in crops (maize, sorghum, rice, and Ae. tauschii) than in Arabidopsis. Cis-element analysis in the ZmSSL gene promoter region revealed that most genes contained many development and stress response elements. We evaluated the expression levels of ZmSSL genes under normal conditions and stress treatments. ZmSSL4–9 were widely expressed in different tissues and were positively or negatively regulated by heat, cold, and infection stress from Colletotrichum graminicola and Cercospora zeina. Moreover, ZmSSL4 and ZmSSL5 were localized in the chloroplast. Taken together, we provide insight into the evolutionary relationships of the ZmSSL genes, which would be useful to further identify the potential functions of ZmSSLs in maize. [ABSTRACT FROM AUTHOR]

Camptothecin (CPT) is a vital monoterpene indole alkaloid used in anti-cancer therapeutics. It is primarily derived from Camptotheca acuminata and Nothapodytes nimmoniana plants that are indigenous to Southeast Asia. Plants have intricate metabolic networks and use them to produce secondary metabolites such as CPT, which is a prerequisite for rational metabolic engineering design to optimize their production. By reconstructing metabolic models, we can predict plant metabolic behavior, facilitating the selection of suitable approaches and saving time, cost, and energy, over traditional hit and trial experimental approaches. In this study, we reconstructed a genome-scale metabolic model for N. nimmoniana (NothaGEM iSM1809) and curated it using experimentally obtained biochemical data. We also used in silico tools to identify and rank suitable enzyme targets for overexpression and knockout to maximize camptothecin production. The predicted over-expression targets encompass enzymes involved in the camptothecin biosynthesis pathway, including strictosidine synthase and geraniol 10-hydroxylase, as well as targets related to plant metabolism, such as amino acid biosynthesis and the tricarboxylic acid cycle. The top-ranked knockout targets included reactions responsible for the formation of folates and serine, as well as the conversion of acetyl CoA and oxaloacetate to malate and citrate. One of the top-ranked overexpression targets, strictosidine synthase, was chosen to generate metabolically engineered cell lines of N. nimmoniana using Agrobacterium tumefaciensmediated transformation. The transformed cell line showed a 5-fold increase in camptothecin production, with a yield of up to 5 µg g-1. [ABSTRACT FROM AUTHOR]

The strictosidine synthase-like (SSL) gene family is a small plant immune-regulated gene family that plays a critical role in plant resistance to biotic/abiotic stresses. To date, very little has been reported on the SSL gene in plants. In this study, a total of thirteen SSLs genes were identified from poplar, and these were classified into four subgroups based on multiple sequence alignment and phylogenetic tree analysis, and members of the same subgroup were found to have similar gene structures and motifs. The results of the collinearity analysis showed that poplar SSLs had more collinear genes in the woody plants Salix purpurea and Eucalyptus grandis. The promoter analysis revealed that the promoter region of PtrSSLs contains a large number of biotic/abiotic stress response elements. Subsequently, we examined the expression patterns of PtrSSLs following drought, salt, and leaf blight stress, using RT-qPCR to validate the response of PtrSSLs to biotic/abiotic stresses. In addition, the prediction of transcription factor (TF) regulatory networks identified several TFs, such as ATMYB46, ATMYB15, AGL20, STOP1, ATWRKY65, and so on, that may be induced in the expression of PtrSSLs in response to adversity stress. In conclusion, this study provides a solid basis for a functional analysis of the SSL gene family in response to biotic/abiotic stresses in poplar. [ABSTRACT FROM AUTHOR]

Strictosidine synthase (STR) catalyzes the Pictet–Spengler (PS) reaction of tryptamine and secologanin to produce strictosidine. Recent studies demonstrated that the enzyme can also catalyze the reaction of non‐natural substrates to form new alkaloid skeletons. For example, the PS condensation of 1H‐indole‐4‐ethanamine with secologanin could be promoted by the STR from Rauvolfia serpentina (RsSTR) to generate a rare class of skeletons with a seven‐membered ring, namely azepino‐[3,4,5‐cd]‐indoles, which are precursors for the synthesis of new compounds displaying antimalarial activity. In the present study, the detailed reaction mechanism of RsSTR‐catalyzed formation of the rare seven‐membered azepino‐indole skeleton through the PS reaction was revealed at the atomic level by quantum chemical calculations. The structures of the transition states and intermediates involved in the reaction pathway were optimized, and the energetics of the complete reaction were analyzed. Based on our calculation results, the most likely pathway of the enzyme‐catalyzed reaction was determined, and the rate‐determining step of the reaction was clarified. The mechanistic details obtained in the present study are important in understanding the promiscuous activity of RsSTR in the formation of the rare azepino‐indole skeleton molecule and are also helpful in designing STR enzymes for the synthesis of other new alkaloid skeleton molecules. [ABSTRACT FROM AUTHOR]

Camptothecin (CPT) is a vital monoterpene indole alkaloid used in anti-cancer therapeutics. It is primarily derived from Camptotheca acuminata and Nothapodytes nimmoniana plants that are indigenous to Southeast Asia. Plants have intricate metabolic networks and use them to produce secondary metabolites such as CPT, which is a prerequisite for rational metabolic engineering design to optimize their production. By reconstructing metabolic models, we can predict plant metabolic behavior, facilitating the selection of suitable approaches and saving time, cost, and energy, over traditional hit and trial experimental approaches. In this study, we reconstructed a genome-scale metabolic model for N. nimmoniana (NothaGEM iSM1809) and curated it using experimentally obtained biochemical data. We also used in silico tools to identify and rank suitable enzyme targets for overexpression and knockout to maximize camptothecin production. The predicted over-expression targets encompass enzymes involved in the camptothecin biosynthesis pathway, including strictosidine synthase and geraniol 10-hydroxylase, as well as targets related to plant metabolism, such as amino acid biosynthesis and the tricarboxylic acid cycle. The top-ranked knockout targets included reactions responsible for the formation of folates and serine, as well as the conversion of acetyl CoA and oxaloacetate to malate and citrate. One of the top-ranked overexpression targets, strictosidine synthase, was chosen to generate metabolically engineered cell lines of N. nimmoniana using Agrobacterium tumefaciens-mediated transformation. The transformed cell line showed a 5-fold increase in camptothecin production, with a yield of up to 5 µg g−1.

Abstract Strictosidine synthase (STR) catalyzes the Pictet–Spengler (PS) reaction of tryptamine and secologanin to produce strictosidine. Recent studies demonstrated that the enzyme can also catalyze the reaction of non‐natural substrates to form new alkaloid skeletons. For example, the PS condensation of 1H‐indole‐4‐ethanamine with secologanin could be promoted by the STR from Rauvolfia serpentina (RsSTR) to generate a rare class of skeletons with a seven‐membered ring, namely azepino‐[3,4,5‐cd]‐indoles, which are precursors for the synthesis of new compounds displaying antimalarial activity. In the present study, the detailed reaction mechanism of RsSTR‐catalyzed formation of the rare seven‐membered azepino‐indole skeleton through the PS reaction was revealed at the atomic level by quantum chemical calculations. The structures of the transition states and intermediates involved in the reaction pathway were optimized, and the energetics of the complete reaction were analyzed. Based on our calculation results, the most likely pathway of the enzyme‐catalyzed reaction was determined, and the rate‐determining step of the reaction was clarified. The mechanistic details obtained in the present study are important in understanding the promiscuous activity of RsSTR in the formation of the rare azepino‐indole skeleton molecule and are also helpful in designing STR enzymes for the synthesis of other new alkaloid skeleton molecules.

Plant-derived monoterpene indole alkaloids (MIAs) from Uncaria rhynchophylla (UR) have huge medicinal properties in treating Alzheimer's disease, Parkinson's disease, and depression. Although many bioactive UR-MIA products have been isolated as drugs, their biosynthetic pathway remains largely unexplored. In this study, untargeted metabolome identified 79 MIA features in UR tissues (leaf, branch stem, hook stem, and stem), of which 30 MIAs were differentially accumulated among different tissues. Short time series expression analysis captured 58 pathway genes and 12 hub regulators responsible for UR-MIA biosynthesis and regulation, which were strong links with main UR-MIA features. Coexpression networks further pointed to two strictosidine synthases (UrSTR1/5) that were coregulated with multiple MIA-related genes and highly correlated with UR-MIA features (r > 0.7, P < 0.005). Both UrSTR1/5 catalyzed the formation of strictosidine with tryptamine and secologanin as substrates, highlighting the importance of key residues (UrSTR1 : Glu309, Tyr155; UrSTR5 : Glu295, Tyr141). Further, overexpression of UrSTR1/5 in UR hairy roots constitutively increased the biosynthesis of bioactive UR-MIAs (rhynchophylline, isorhynchophylline, corynoxeine, etc), whereas RNAi of UrSTR1/5 significantly decreased UR-MIA biosynthesis. Collectively, our work not only provides candidates for reconstituting the biosynthesis of bioactive UR-MIAs in heterologous hosts but also highlights a powerful strategy for mining natural product biosynthesis in medicinal plants. [ABSTRACT FROM AUTHOR]

Maize is often subjected to various environmental stresses. The strictosidine synthase-like (SSL) family is thought to catalyze the key step in the monoterpene alkaloids synthesis pathway in response to environmental stresses. However, the role of ZmSSL genes in maize growth and development and its response to stresses is unknown. Herein, we undertook the systematic identification and analysis of maize SSL genes. Twenty SSL genes were identified in the maize genome. Except for chromosomes 3, 5, 6, and 10, they were unevenly distributed on the remaining 6 chromosomes. A total of 105 SSL genes from maize, sorghum, rice, Aegilops tauschii, and Arabidopsis were divided into five evolutionary groups, and ZmSSL gene structures and conserved protein motifs in the same group were similar. A collinearity analysis showed that tandem duplication plays an important role in the evolution of the SSL family in maize, and ZmSSL genes share more collinear genes in crops (maize, sorghum, rice, and Ae. tauschii) than in Arabidopsis. Cis-element analysis in the ZmSSL gene promoter region revealed that most genes contained many development and stress response elements. We evaluated the expression levels of ZmSSL genes under normal conditions and stress treatments. ZmSSL4–9 were widely expressed in different tissues and were positively or negatively regulated by heat, cold, and infection stress from Colletotrichum graminicola and Cercospora zeina. Moreover, ZmSSL4 and ZmSSL5 were localized in the chloroplast. Taken together, we provide insight into the evolutionary relationships of the ZmSSL genes, which would be useful to further identify the potential functions of ZmSSLs in maize.

The strictosidine synthase-like (SSL) gene family is a small plant immune-regulated gene family that plays a critical role in plant resistance to biotic/abiotic stresses. To date, very little has been reported on the SSL gene in plants. In this study, a total of thirteen SSLs genes were identified from poplar, and these were classified into four subgroups based on multiple sequence alignment and phylogenetic tree analysis, and members of the same subgroup were found to have similar gene structures and motifs. The results of the collinearity analysis showed that poplar SSLs had more collinear genes in the woody plants Salix purpurea and Eucalyptus grandis. The promoter analysis revealed that the promoter region of PtrSSLs contains a large number of biotic/abiotic stress response elements. Subsequently, we examined the expression patterns of PtrSSLs following drought, salt, and leaf blight stress, using RT-qPCR to validate the response of PtrSSLs to biotic/abiotic stresses. In addition, the prediction of transcription factor (TF) regulatory networks identified several TFs, such as ATMYB46, ATMYB15, AGL20, STOP1, ATWRKY65, and so on, that may be induced in the expression of PtrSSLs in response to adversity stress. In conclusion, this study provides a solid basis for a functional analysis of the SSL gene family in response to biotic/abiotic stresses in poplar.

SUMMARY: Neolamarckia cadamba (Roxb.), a close relative of Coffea canephora and Ophiorrhiza pumila, is an important traditional medicine in Southeast Asia. Three major glycosidic monoterpenoid indole alkaloids (MIAs), cadambine and its derivatives 3β‐isodihydrocadambine and 3β‐dihydrocadambine, accumulate in the bark and leaves, and exhibit antimalarial, antiproliferative, antioxidant, anticancer and anti‐inflammatory activities. Here, we report a chromosome‐scale N. cadamba genome, with 744.5 Mb assembled into 22 pseudochromosomes with contig N50 and scaffold N50 of 824.14 Kb and 29.20 Mb, respectively. Comparative genomic analysis of N. cadamba with Co. canephora revealed that N. cadamba underwent a relatively recent whole‐genome duplication (WGD) event after diverging from Co. canephora, which contributed to the evolution of the MIA biosynthetic pathway. We determined the key intermediates of the cadambine biosynthetic pathway and further showed that NcSTR1 catalyzed the synthesis of strictosidine in N. cadamba. A new component, epoxystrictosidine (C27H34N2O10, m/z 547.2285), was identified in the cadambine biosynthetic pathway. Combining genome‐wide association study (GWAS), population analysis, multi‐omics analysis and metabolic gene cluster prediction, this study will shed light on the evolution of MIA biosynthetic pathway genes. This N. cadamba reference sequence will accelerate the understanding of the evolutionary history of specific metabolic pathways and facilitate the development of tools for enhancing bioactive productivity by metabolic engineering in microbes or by molecular breeding in plants. Significance Statement: Coffea canephora, Ophiorrhiza pumila and Neolamarckia cadamba are three closely‐related species in the Rubiaceae family that produce quite different major specialized metabolites including caffeine (a purine alkaloid), camptothecin (anti‐cancer MIAs) and cadambine. This chromosome‐level assembly of N. cadamba genome and analysis of the cadambine synthetic pathway will not only facilitate the development of tools for enhancing bioactive productivity, through metabolic engineering, but will also accelerate our understanding of the evolutionary history of specific metabolic pathways. [ABSTRACT FROM AUTHOR]

• Combinatory effect of MeJa and UV-B on TDC and STR expression was studied. • Vinblastine, vincristine and ajamilicine in treated plants were determined by HPLC. • MeJa treatment has an opposite effect on TDC and STR. • UV-B elicitation increased the expression of the genes in most cases. • MU60 is the choice for vinblastine, vincristine and ajmalicine high production. Catharanthus roseus is a very rich source of medically important alkaloids. However, since their concentrations are extremely low in plant tissues, many efforts have been made to increase the alkaloids level - among them are the application of various elicitors. Since the alkaloids are synthetized by a complex pathway, the detailed knowledge of the molecular background of the system is essential. The current job aimed to study the effect of two elicitor, methyl jasmonate (MeJa) and UV-B irradiation, and also their simultaneous effect, on the expression patterns of two key synthesis-involved genes, namely tryptophan decarboxylase and strictosidine synthase through quantitative RT-PCR. Estimation of vinblastine, vincristine and ajmalicine, was carried out using high performance liquid chromatography (HPLC) in the elicited plant leaves. From the obtained results, it was concluded, that these two elicitors act on different way, and also their combined application induces the tryptophan decarboxylase but in less for the strictosidine synthase gene expression in the treated Catharanthus roseus leaves. The results showed that the combination of MeJa and UV-B light (MU) induces higher accumulation of vinblastine,vincristine and ajmalicine than other treatments. Vinblastine content with MU60 treatment showed higher level during the third day of exposure to the combined elicitors (methyl jasmonate and UV-B). Vincristine accumulation was the highest after one day of exposure to MU60 treatment. Its content was increased 6-fold than control after one day exposure to the combined elicitors. Additionally, it could be observed that MU60 treatment, was the best for ajmalicine accumulation. Ajmalicine content was increased 8-fold than control at 60 min exposure to the combined elicitors. As a final outcome, we also conclude that the effect of the different elicitations is highly dependent on the experimental parameters. [ABSTRACT FROM AUTHOR]

Terpenoid indole (TIAs) and β -carboline alkaloids (BCAs), such as suppressant reserpine, vasodilatory yohimbine, and antimalarial quinine, are natural compounds derived from strictosidine. These compounds can exert powerful pharmacological effects but be obtained from limited source in nature. the whole biosynthetic pathway of TIAs and BCAs, The Pictet-Spengler reaction catalyzed by strictosidine synthase (STR; EC: 4.3.3.2) is the rate-limiting step. Therefore, it is necessary to investigate their biosynthesis pathways, especially the role of STR, and related findings will support the biosynthetic generation of natural and unnatural compounds. This review summarizes the latest studies concerning the function of STR in TIA and BCA biosynthesis, and illustrates the compounds derived from strictosidine. The substrate specificity of STR based on its structure is also summarized. Proteins that contain six-bladed four-stranded β -propeller folds in many organisms, other than plants, are listed. The presence of these folds may lead to similar functions among organisms. The expression of STR gene can greatly influence the production of many compounds. STR is mainly applied to product various valuable drugs in plant cell suspension culture and biosynthesis in other carriers. [Display omitted] [ABSTRACT FROM AUTHOR]

Nothapodytes foetida, an endangered tree of Indian origin, is a major source of the anti-cancer monoterpenoid indole alkaloid, camptothecin (CPT). Strictosidine synthase (STR) condenses tryptamine and secologanin to form strictosidine, a universal precursor of terpenoid indole alkaloids including CPT. We cloned full-length str cDNA with an open reading frame of 1059 bp from N. foetida (Nfstr) using a homology-based approach. Different tissues of N. foetida from in vitro grown cultures, as well as a mature tree, showed expression of STR, confirming the constitutive nature of the gene. In vitro tissues showed a positive correlation between STR expression and the CPT content, but tissues from wild-type mature plants did not show a similar pattern. Transgenic Ophiorrhiza rugosa plants overexpressing Nfstr showed 1.9-fold higher CPT than non-transformed plants. The results indicated that overexpression of Nfstr in target plants could improve the levels of CPT and may provide an alternative and sustainable source of camptothecin. Key message: We report the full-length sequence and expression analysis of strictosidine synthase cDNA from Nothapodytes foetida (Nfstr). Further, the overexpression of Nfstr in Ophiorrhiza resulted in twofold enhancement in camptothecin levels. [ABSTRACT FROM AUTHOR]

MicroRNA1916 (miR1916) is one of the nonconserved miRNAs that respond to various stresses in plants, but little has been known at present about its mechanisms in biotic stresses. In this study, the expression of Solanum lycopersicum (sly)‐miR1916 in tomato was found to be down‐regulated after infection with Phytophthora infestans or Botrytis cinerea. Tomato plants that overexpressed sly‐miR1916 displayed significant enhancement in susceptibility to P. infestans and B. cinerea infection, as well as increased tendency to produce reactive oxygen species. Silencing of sly‐miR1916 by short tandem target mimic and artificial microRNA strategies caused the tomato plants to become more tolerant to adverse conditions. In addition, lower sly‐miR1916 expression could up‐regulate the expression of strictosidine synthase (STR‐2), UDP‐glycosyltransferases (UGTs), late blight resistance protein homolog R1B‐16, disease resistance protein RPP13‐like, and MYB transcription factor (MYB12), which ultimately resulted in the accumulation of α‐tomatine and anthocyanins via STR‐2, UGT, and MYB12. Furthermore, ectopic expression of sly‐miR1916/STR‐2 significantly changed the tolerance of tobacco to B. cinerea. Taken together, the results demonstrated that sly‐miR1916 might regulate the expression of STR‐2, UGT, and MYB12 in tomato plant, conferring sensitivity to biotic stress via modulating α‐tomatine and anthocyanins. The sly‐miR1916 acts as negative regulator of defense responses against Phytophthora infestans and Botrytis cinerea infection via modulating STR‐2, UGT, R1B‐16, RPP13‐like and MYB12, α‐tomatine and anthocyanins. [ABSTRACT FROM AUTHOR]

Terpenoid indole alkaloid (TIA) biosynthetic pathway of Catharanthus roseus possesses the major attention in current metabolic engineering efforts being the sole source of highly expensive antineoplastic molecules vinblastine and vincristine. The entire TIA pathway is fairly known at biochemical and genetic levels except the pathway steps leading to biosynthesis of catharanthine and tabersonine. To increase the in-planta yield of these antineoplastic metabolites for the pharmaceutical and drug industry, extensive plant tissue culture-based studies were performed to provide alternative production systems. However, the strict spatiotemporal developmental regulation of TIA biosynthesis has restricted the utility of these cultures for large-scale production. Therefore, the present study was performed to enhance the metabolic flux of TIA pathway towards the biosynthesis of vinblastine by overexpressing two upstream TIA pathway genes, tryptophan decarboxylase (CrTDC) and strictosidine synthase (CrSTR), at whole plant levels in C. roseus. Whole plant transgenic of C. roseus was developed using Agrobacterium tumefaciens LBA1119 strain having CrTDC and CrSTR gene cassette. Developed transgenic lines demonstrated up to twofold enhanced total alkaloid production with maximum ninefold increase in vindoline and catharanthine, and fivefold increased vinblastine production. These lines recorded a maximum of 38-fold and 65-fold enhanced transcript levels of CrTDC and CrSTR genes, respectively. [ABSTRACT FROM AUTHOR]

Alkaloids are the main active ingredients in the medicinal plant Dendrobium officinale. Based on the published genomic and transcriptomic data, a proposed terpenoid indole alkaloid (TIA) biosynthesis pathway may be present in D. officinale. In this study, protocorm-like bodies (PLBs) with a high-yielding production of alkaloids were obtained by the optimization of tryptophan, secologanin and methyl jasmonate (MeJA) treatment. The results showed that the total alkaloid content was 2.05 times greater than that of the control group when the PLBs were fed with 9 μM tryptophan, 6 μM secologanin and 100 μM MeJA after 36 days. HPLC analysis showed that strictosidine synthase (STR) activity also increased in the treated plants. A total of 78 metabolites were identified using gas chromatography-mass spectrometry (GC-MS) in combination with liquid chromatography-mass spectrometry (LC-MS) methods; 29 differential metabolites were identified according to the multivariate statistical analysis. Among them, carapanaubine, a kind of TIA, exhibited dramatically increased levels. In addition, a possible underlying process of the metabolic flux from related metabolism to the TIA biosynthetic pathway was enhanced. These results provide a comprehensive view of the metabolic changes related to alkaloid biosynthesis, especially TIA biosynthesis, in response to tryptophan, secologanin and MeJA treatment. [ABSTRACT FROM AUTHOR]

Main conclusion A Catharanthus roseus mutant accumulates high levels of ajmalicine at the expense of catharanthine and vindoline. The altered chemistry depends on increased expression and biochemical activities of strictosidine ß-glucosidase and ajmalicine synthase activities and reduced expression and biochemical activity of geissoschizine synthase. The Madagascar periwinkle [Catharanthus roseus (L.) G. Don] is a commercially important horticultural flower species and is a valuable source for several monoterpenoid indole alkaloids (MIAs), such as the powerful antihypertensive drug ajmalicine and the antineoplastic agents, vinblastine and vincristine. While biosynthesis of the common MIA precursor strictosidine and its reactive aglycones has been elucidated, the branch point steps leading to the formation of different classes of MIAs remain poorly characterized. Screening of 3600 ethyl methyl sulfonate mutagenized C. roseus plants using a simple thin-layer chromatography screen yielded a mutant (M2-0754) accumulating high levels of ajmalicine together with significantly lower levels of catharanthine and vindoline. Comparative bioinformatic analyses, virus-induced gene silencing, and biochemical characterization identified geissoschizine synthase, the gateway enzyme that controls flux for the formation of iboga and aspidosperma MIAs. The reduction of geissoschizine synthase transcripts in this high ajmalicine mutant, together with increased transcripts and enzyme activities of strictosidine β-glucosidase and of heteroyohimbine synthase, explains the preferential formation of ajmalicine in the mutant instead of catharanthine and vindoline that accumulates in the wild-type parent. Reciprocal crosses established that that the high ajmalicine phenotype is inherited as a Mendelian recessive trait. [ABSTRACT FROM AUTHOR]

[Display omitted] • The metabolomics and transcriptomics of hook, leaf and stem of Uncaria rhynchophylla were analyzed. • A proposal biosynthetic pathway for TOAs was fully devised. • Three enzymes, tryptophan decarboxylase TDC, STR and SGD, were identified for the first time in Uncaria rhynchophylla. Tetracyclic oxindole alkaloids (TOAs), main active ingredients of Uncaria rhynchophylla (UR) , has inspired the interest of pharmacologists and chemists because of its great potential in the treatment of the diseases of the nervous system and cardiovascular system and its special spirooxindole scaffold, but the biosynthetic pathway of this compounds is still unknown. In this work, the metabolomics and transcriptomics of hook, leaf and stem of UR were analyzed, and 31 alkaloids and 47,423 unigenes were identified, as well as the relative contents of these alkaloids were evaluated. Based on the above results and literatures, a proposal biosynthetic pathway for TOAs was devised. Furthermore, three unigenes were suggested mediating the biosynthesis of TOAs through the integrated analysis of metabolomics and transcriptomics, and three enzymes, tryptophan decarboxylase, strictosidine synthase and strictosidine- β - d -glucosidase, were identified as important catalytic enzymes for the synthesis of tryptamine, strictosidine (7) and 4,21-dehydrogeissochizine, respectively, which are considered as the important precursors of TOAs. [ABSTRACT FROM AUTHOR]

A fast regenerating Agrobacterium tumefaciens-mediated transformation protocol for Bacopa monnieri (L.) Wettst. was developed as a model system for heterologous expression of terpenoid indole alkaloid pathway genes from Catharanthus roseus (L.) G. Don. The direct regeneration of shoots from leaf explants co-cultured with A. tumefaciens resulted in the integration of a tryptophan decarboxylase ( tdc) and strictosidine synthase ( str) cassette () in the regenerated progeny. The highest transformation efficiency (83.88%) was achieved when leaf explants were infected on the adaxial laminar surface by manual pricking with 48- to 72-h-old suspensions (OD = 0.5-0.6) of A. tumefaciens strain LBA1119 (carrying the binary vector pMOG22). The heterologous expression of tryptophan decarboxylase and strictosidine synthase genes that are otherwise not present in B. monnieri plants was confirmed through semi-quantitative PCR and metabolite quantification assays. The entire protocol duration from co-cultivation through regeneration of transgenic plants to their establishment in the glass house took 40-45 d. The developed B. monnieri model can be used to test expression cassettes carrying genes for plant secondary metabolic pathway engineering, especially those genes that are expressed in differentiated cell, tissue, or organs. [ABSTRACT FROM AUTHOR]

Introduction: Hamelia patens is a perennial shrub native from Mexico which is used in traditional medicine to treat chronic wounds and tumors. Bioactive monoterpenoid indole alkaloids (MIAs) and monoterpenoid oxindole alkaloids (MOAs) have been isolated from this species, associated with the ethnomedical use. Objectives: In order to study the biosynthesis and production of these alkaloids, H. patens plants were treated with the stress hormone jasmonic acid. Methods: Nuclear magnetic resonance-based metabolic profiles and multivariate data analysis were applied to explore changes or variability in elicited and control plants. Results: According to the partial least square-discriminant analysis from MeOH/HO fractions, sucrose, tryptophan, glutamic acid, glutamine, strictosidine, p-coumaric acid, chlorogenic acid, and the MOAs isopteropodine, palmirine and pteropodine were predominant in the treated plants, while glucose, aspartic acid, acetic acid, and loganic acid concentrations were higher in control plants. HPLC analysis showed that accumulation of pteropodine, isopteropodine, speciophylline, rumberine, hameline and palmirine in elicited plants was preceded by an increase in the transcription level of 1-deoxy- d-xylulose-5-phosphate synthase (DXS, EC 2.2.1.7) and strictosidine synthase (STR, EC 4.3.3.2), and STR activity during a time course. However, no inductions of transcription and enzyme activity of strictosidine β-glucosidase (SGD, EC 3.2.1.105) were observed in elicited plants. Conclusion: Correlations between primary and secondary metabolism biosynthetic pathways, such as the alkaloid and chlorogenic acid biosynthesis were found. Also, their implications in the plant fitness to stress are proposed. Confirmation of tryptophan as a precursor of MIA and MOA, via shikimate pathway, was done by L-[3′-C]-tryptophan feeding. [ABSTRACT FROM AUTHOR]

Camptothecin (CPT), a monoterpene indole alkaloid, is a potent inhibitor of DNA topoisomerase I and has applications in treating ovarian, small lung and refractory ovarian cancers. Stem wood tissue of Nothapodytes nimmoniana (Graham) Mabb. (family Icacinaceae) is one of the richest sources of CPT. Since there is no genomic or transcriptome data available for the species, the present work sequenced and analysed transcriptome of stem wood tissue on an Illumina platform. From a total of 77,55,978 reads, 9,187 transcripts were assembled with an average length of 255 bp. Functional annotation and categorization of these assembled transcripts unraveled the transcriptome architecture and also a total of 13 genes associated with CPT biosynthetic pathway were identified in the stem wood tissue. Four genes of the pathway were cloned to full length by RACE to validate the transcriptome data. Expression analysis of 13 genes associated with CPT biosynthetic pathway in 11 different tissues vis-à-vis CPT content analysis suggested an important role of NnPG10H, NnPSLS and NnPSTR genes in the biosynthesis of CPT. These results indicated that CPT might be synthesized in the leaves and then perhaps exported to stem wood tissue for storage. [ABSTRACT FROM AUTHOR]

The Rauvolfia serpentina strictosidine synthase (RsSTR) enzyme with a bisubstrate activity is central to monoterpenoid indole alkaloid (MIA) biosynthesis pathways, as it stereoselectively condenses the terpenoid and indole metabolites, secologanin and tryptamine, respectively, into strictosidine. Here, cooperativity was aimed to be deciphered by proxy with help of a non-substrate tryptamine analog (decoy compound) to allow a bisubstrate binding without reaction, facilitating an isothermal titration calorimetry (ITC)-based analysis of the effect of the presence of one substrate on the binding of the other. Tryptamine and tryptamine analog bound to RsSTR with similar binding affinities (K d ). On the contrary, ITC revealed an exothermic titration of secologanin to RsSTR but could not fully quantify it because of weak binding. Interestingly, secologanin bound to RsSTR with an apparent binding affinity (K d,app ) of 212.1 μM in the presence of the decoy compound, as opposed to a lack of binding to RsSTR alone, strongly suggesting a "tryptamine-first" mode of binding. Conversely, binding of tryptamine analog in the presence of secologanin was enhanced >3-fold. Further, molecular dynamics simulation (MDS) analyses revealed the conformational flexibility needed for such cooperativity. Our binding studies complemented with the computational analyses suggested cooperativity in the ordered bisubstrate binding to RsSTR. Therefore, understanding thermodynamics and cooperativity in the binding of substrates or ligands would help to unravel the mechanism of enzyme catalysis and ligand-receptor interactions, and would guide the redesign of enzymes for enhanced properties and the design of inhibitors against enzymes and receptors.Communicated by Ramaswamy H. Sarma.

Tryptophan decarboxylase (TDC) and strictosidine synthase (STR) genes from Catharanthus roseus have been successfully over-expressed in the rol gene integrated cell suspensions of V. minor. Thirty seconds SAAT (sonication-assisted Agrobacterium transformation) treatment of plant cell suspension with LBA1119 having construct () generated three stable TDC + STR over-expressing cell lines-PVG1, PVG2, and PVG3. The transgenes were confirmed by β-glucuronidase GUS histochemical assay and PCR amplification of rol genes/GUS gene. All the three cell suspension lines were found to be slow growing. In comparison to the control cell suspensions (GI = 241.0 ± 5.8), PVG3 cell line registered a growth index (GI) of 208.0 ± 10.0 followed by PVG1 (GI = 140.0 ± 14.2) and PVG2 (GI = 85.0 ± 9.6). The PVG3 cell line was also up-scaled in the 5-l stirred tank bioreactor with GI of 745.6 ± 35.3 under optimized parameters. Only PVG3 line registered a twofold increase in total alkaloid content (2.1 ± 0.1 % dry wt.) and showed vincamine presence (0.003 ± 0.001 % dry wt.) which was further enhanced at the bioreactor level (2.7 ± 0.3 and 0.005 ± 0.001 % dry wt., respectively). Real-time (RT) qPCR analysis of PVG3 showed more than sevenfold to eightfold increase in TDC and STR expression [relative quantity value (RQ) = 7.6 ± 0.8 (TDC); RQ = 8.5 ± 0.9 (STR)]. [ABSTRACT FROM AUTHOR]

Strictosidine synthases catalyze the formation of strictosidine, a key intermediate in the biosynthesis of a large variety of monoterpenoid indole alkaloids. Efforts to utilize these biocatalysts for the preparation of strictosidine analogs have however been of limited success due to the high substrate specificity of these enzymes. We have explored the impact of a protein engineering approach called circular permutation on the activity of strictosidine synthase from the Indian medicinal plant Rauvolfia serpentina . To expedite the discovery process, our study departs from the usual process of creating a random protein library, followed by extensive screening. Instead, a small, focused library of circular permutated variants of the six bladed β-propeller protein was prepared, specifically probing two regions which cover the enzyme active site. The observed activity changes suggest important roles of both regions in protein folding, stability and catalysis. [ABSTRACT FROM AUTHOR]

The activity and gene expression of strictosidine-related enzymes in Uncaria tomentosa root cultures exposed to oxidative stress were studied. Elicitation with 0.2 mM hydrogen peroxide (H2O2) or a combination of 0.8 mM buthionine sulfoximine and 0.2 mM jasmonic acid (BSO-JA) increased peroxidase activities by twofold at Day 8 and glutathione reductase by 1.4-fold at Day 5 in H2O2 elicited cultures respect to the control. Production of monoterpenoid oxindole alkaloids (MOA), 3α-dihydrocadambine, and dolichantoside was stimulated after H2O2 elicitation, reaching levels of 886.4 ± 23.6, 847.7 ± 25.4, and 87.5 ± 7.2 µg/g DW, at Day 8 which were 1.7-, 2.1-, and 2.3-fold higher relative to control. BSO-JA elicited cultures produced about twice alkaloids than H2O2-treated cultures, following a biphasic pattern with maxima at 0.5 and 8 days. Alkaloid production was preceded by increase in strictosidine synthase (STR) and strictosidine glucosidase (SGD) activities. After elicitation with H2O2 or BSO-JA, the STR activity (pKat/mg protein) increased by 1.9-fold (93.8 ± 17.8 at 24 h) or 2.5-fold (102.4 ± 2.2 at 6 h) and the SGD activity (pKat/mg protein) by 2.8-fold (245.2 ± 14.4 at 6 h) or 4.2-fold (421.2 ± 1.8 at 18 h) relative to control. STR and SGD transcripts were upregulated after elicitation. H2O2-treated roots showed higher levels of STR at 48-192 h and SGD at 24-48 h, while BSO-JA treatments showed STR increased at 12 h and SGD at 24 h. Also, LC/ESI-MS confirmed the biosynthesis of dolichantoside from N-ω-methyltryptamine and secologanin by U. tomentosa protein extracts. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 29:621-630, 2013 [ABSTRACT FROM AUTHOR]

The article discusses specialized metabolism of enzymes. It defines specialized metabolism as the metabolic pathways synthesizing chemicals that are not immediately required for host organism survival but play a role in the reproductive success in complex ecosystems. It presents some new catalytic mechanisms emerging from specialized metabolic systems, one is the strictosidine synthase (STR) activity. It explores the role of catalytic promiscuity in the ability of the enzyme to evolve.

Camptothecin is one of the clinically used anticancer compounds derived from plants. We have established a hairy root culture Ophiorrhiza pumila, which efficiently produces camptothecin. The strictosidine synthase cDNA was obtained from O. pumila, and its properties were characterized using recombinant protein expressed in Escherichia coli. The mechanisms of camptothecin transport and self-resistance of producing plant cells have also been investigated. These studies offer a basis for pathway engineering of camptothecin in the future. [ABSTRACT FROM AUTHOR]

We isolated lap3-1 and lap3-2 mutants in a screen for pollen that displays abnormal stigma binding. Unlike wild-type pollen, lap3-1 and lap3-2 pollen exine is thinner, weaker, and is missing some connections between their roof-like tectum structures. We describe the mapping and identification of LAP3 as a novel gene that contains a repetitive motif found in β-propeller enzymes. Insertion mutations in LAP3 lead to male sterility. To investigate possible roles for LAP3 in pollen development, we assayed the metabolite profile of anther tissues containing developing pollen grains and found that the lap3-2 defect leads to a broad range of metabolic changes. The largest changes were seen in levels of a straight-chain hydrocarbon nonacosane and in naringenin chalcone, an obligate compound in the flavonoid biosynthesis pathway. [ABSTRACT FROM AUTHOR]