Nelumbo nucifera leaves extract ameliorated scopolamine-induced cognition impairment via enhanced adult hippocampus neurogenesis

In this presentation, we explored the molecular mechanisms of N. nucifera leaf water extracts (NLWEs) and polyphenol extract (NLPE) on scopolamine-induced cell apoptosis and cognition defects. The administration of NLWE and NLPE did not alter the body weight and serum biomarker rs and significantly ameliorated scopolamine-induced cognition impairment according to Y-maze test analysis. In mice, treatment with scopolamine disrupted normal histoarchitecture in the hippocampus, whereas the administration of NLWE and NLPE reversed the phenomenon. Western blot analysis revealed that scopolamine mitigated the expression of doublecortin (DCX), nestin, and NeuN, and cotreatment with NLWE or NLPE significantly recovered the expression of these proteins. NLWE and NLPE upregulated DCX and NeuN expression in the hippocampus region, as evidenced by immunohistochemical staining analysis of scopolamine-treated mice. NLWE and NLPE obviously elevated brain-derived neurotrophic factor (BDNF) and enhanced its downstream proteins activity. NLWE and NLPE attenuated scopolamine-induced apoptosis by reducing Bax and increased Bcl-2 expression. In addition, scopolamine also triggered apoptosis in human neuroblastoma SH-SY5Y cells whereas co-treatment with NLWE or quercetin-3-glucuronide (Q3G) reversed the phenomenon. NLWE or Q3G enhanced Bcl-2 and reduced Bax expression in the presence of scopolamine in SH-SY5Y cells. NLWE or Q3G recovered the inhibitory effects of scopolamine on neurogenesis and BDNF signals in SH-SY5Y cells. Overall, our results revealed that N. nucifera leaf extracts and Q3G promoted adult hippocampus neurogenesis and prevented apoptosis to mitigate scopolamine-induced cognition dysfunction through the regulation of BDNF signaling pathway.

Total alkaloids from the seed embryo of Nelumbo nucifera Gaertn. improve cognitive impairment in APP/PS1 mice and protect Aβ-damaged PC12 cells

The seed embryo of Nelumbo nucifera Gaertn. is a famous traditional Chinese medicine and food which is considered conducive to the prevention of Alzheimer's disease (AD). In this study, the effect and mechanism of TASENN (total alkaloids from the seed embryo of Nelumbo nucifera Gaertn.) on AD mice and amyloid-β (Aβ) injured PC12 cells were evaluated. HPLC-UV analysis showed that the extracted TASENN (purity = 95.6%) mainly contains Liensinine, Isoliensinine, and Neferine (purity was 23.01, 28.02, and 44.57%, respectively). In vivo, oral treatment with TASENN (50 mg/kg/day for 28 days) improved the learning and memory functions of APP/PS1 transgenic mice, ameliorated the histopathological changes of cortical and hippocampal neurons, and inhibited neuronal apoptosis. We found that TASENN reduced the phosphorylation of Tau and the formation of neurofibrillary tangles (NFTs) in APP/PS1 mouse brain. Moreover, TASENN down-regulated the expression of APP and BACE1, ameliorated Aβ deposition, and inhibited microglial proliferation and aggregation. The elevated protein expression of CaM and p-CaMKII in APP/PS1 mouse brain was also reduced by TASENN. In vitro, TASENN inhibited the apoptosis of PC12 cells injured by Aβ25-35 and increased the cell viability. Aβ25-35-induced increase of cytosolic free Ca2+ level and high expression of CaM, p-CaMKII, and p-Tau were decreased by TASENN. Our findings indicate that TASENN has a potential therapeutic effect on AD mice and a protective effect on PC12 cells. The anti-AD activity of TASENN may be closely related to its negative regulation of the CaM pathway.

Transcription factor NnMYB5 controls petal color by regulating GLUTATHIONE S-TRANSFERASE2 in Nelumbo nucifera

Lotus (Nelumbo spp.) is an important aquatic ornamental genus in the family Nelumbonaceae comprising only 2 species: Nelumbo lutea with yellow flowers and Nelumbo nucifera with red or white flowers. The petal color variations between these 2 species have previously been associated with the potential activities of FLAVONOL SYNTHASE (FLS) and MYB5. However, the underlying genetic mechanisms of flower color divergence within the N. nucifera species remain unclear. Here, quantitative trait locus mapping led to the identification of MYB5, a candidate gene controlling petal color in N. nucifera. Genotyping of 213 natural lotus accessions revealed an 80 kb presence/absence variant (PAV) of the NnMYB5 gene that is associated with petal color variation. Transcriptome analysis, dual-luciferase, and yeast 1-hybrid assays showed that NnMYB5 could directly activate the anthocyanin transporter gene GLUTATHIONE S-TRANSFERASE2 (NnGST2). Heterologous expression of NnGST2 in Arabidopsis (Arabidopsis thaliana) and its overexpression in lotus petals induced anthocyanin accumulation. Deletion of the 80 kb PAV within NnMYB5 inactivated NnGST2 expression and blocked anthocyanin accumulation in white N. nucifera petals. In contrast, the anthocyanin deficiency of N. lutea occurred due to pseudogenized NlMYB5 alleles. Our results establish a regulatory link between NnMYB5 and NnGST2 in petal anthocyanin accumulation and demonstrate the independent mechanisms controlling flower coloration in Nelumbo.

Metabolite profiling and screening of callus browning-related genes in lotus (Nelumbo nucifera)

Callus browning is a major drawback to lotus callus proliferation and regeneration. However, the underlying mechanism of its formation remains largely unknown. Herein, we aimed to explore the metabolic and molecular basis of lotus callus browning by combining histological staining, high-throughput metabolomics, and transcriptomic assays for lotus callus at three browning stages. Histological stained brown callus cross sections displayed severe cell death symptoms, accompanied by an obvious accumulation of polyphenols and lignified materials. Widely targeted metabolomics revealed extensively decreased accumulation of most detected flavonoids and benzylisoquinoline alkaloids (BIAs), as well as a few phenolic acids, amino acids and their derivatives in callus with browning symptoms. Conversely, the contents of most detected tannins were significantly increased. Subsequent comparative transcriptomics identified a set of differentially expressed genes (DEGs) associated with the biosynthesis and regulation of flavonoids and BIAs in lotus. Notably, callus browning was coupled with significantly up-regulated expression of two polyphenol oxidase (PPO) and 17 peroxidase (POD) encoding genes, while the expression of ethylene associated genes remained at marginal levels. These results suggest that lotus callus browning is primarily controlled at the level of metabolism, wherein the oxidation of flavonoids and BIAs is crucially decisive.

Pathway elucidation and microbial synthesis of proaporphine and bis-benzylisoquinoline alkaloids from sacred lotus (Nelumbo nucifera)

Sacred lotus (Nelumbo nucifera) has been utilized as a food, medicine, and spiritual symbol for nearly 3000 years. The medicinal properties of lotus are largely attributed to its unique profile of benzylisoquinoline alkaloids (BIAs), which includes potential anti-cancer, anti-malarial and anti-arrhythmic compounds. BIA biosynthesis in sacred lotus differs markedly from that of opium poppy and other members of the Ranunculales, most notably in an abundance of BIAs possessing the (R)-stereochemical configuration and the absence of reticuline, a major branchpoint intermediate in most BIA producers. Owing to these unique metabolic features and the pharmacological potential of lotus, we set out to elucidate the BIA biosynthesis network in N. nucifera. Here we show that lotus CYP80G (NnCYP80G) and a superior ortholog from Peruvian nutmeg (Laurelia sempervirens; LsCYP80G) stereospecifically convert (R)-N-methylcoclaurine to the proaporphine alkaloid glaziovine, which is subsequently methylated to pronuciferine, the presumed precursor to nuciferine. While sacred lotus employs a dedicated (R)-route to aporphine alkaloids from (R)-norcoclaurine, we implemented an artificial stereochemical inversion approach to flip the stereochemistry of the core BIA pathway. Exploiting the unique substrate specificity of dehydroreticuline synthase from common poppy (Papaver rhoeas) and pairing it with dehydroreticuline reductase enabled de novo synthesis of (R)-N-methylcoclaurine from (S)-norcoclaurine and its subsequent conversion to pronuciferine. We leveraged our stereochemical inversion approach to also elucidate the role of NnCYP80A in sacred lotus metabolism, which we show catalyzes the stereospecific formation of the bis-BIA nelumboferine. Screening our collection of 66 plant O-methyltransferases enabled conversion of nelumboferine to liensinine, a potential anti-cancer bis-BIA from sacred lotus. Our work highlights the unique benzylisoquinoline metabolism of N. nucifera and enables the targeted overproduction of potential lotus pharmaceuticals using engineered microbial systems.

Sleep-promoting activity of lotus (Nelumbo nucifera) rhizome water extract via GABAA receptors

CONTEXT

The sleep-promoting activity of Nelumbo nucifera Gaertn. (Nymphaeaceae) alkaloids in leaves or seeds are well known. However, the sleep-promoting activity of the lotus rhizome (LE), which is used mainly as food, has not yet been evaluated.

OBJECTIVE

We investigated the sleep-promoting activity of LE water extract.

MATERIALS AND METHODS

Institute of Cancer Research (ICR) mice (n = 8) were subject to a pentobarbital-induced sleep test to assess changes in sleep latency and duration following the administration of LE (80-150 mg/kg). In addition, electroencephalography analysis was performed to determine the sleep quality after LE treatment as well as the sleep recovery effect of LE using a caffeine-induced insomnia SD rat model. Real-time PCR and western blot analysis were performed to investigate the expression of neurotransmitter receptors, and the GABA_A receptor antagonists were used for receptor binding analysis.

RESULTS

An oral administration of 150 mg/kg LE significantly increased sleep duration by 24% compared to the control. Furthermore, LE increased nonrapid eye movement (NREM) sleep by increasing theta and delta powers. In the insomnia model, LE increased sleep time by increasing NREM sleep. Moreover, treatment with picrotoxin and flumazenil decreased the sleep time by 33% and 23%, respectively, indicating an involvement of the GABA_A receptor in the sleep-enhancing activity of LE. The expression of GABA_A receptors and the concentration of GABA in the brain were increased by LE.

DISCUSSION AND CONCLUSIONS

The results suggest that the sleep-promoting activity of LE was via the GABA_A receptor. Collectively, these data show that LE may promote sleep.

Novel Insights into Floral Thermogenesis: In Vivo Analyses of Mitochondrial Dynamics in Nelumbo nucifera Flowers

Animal-like thermogenic (TM) activities in flowers have been reported in several families of seed plants. While an association of mitochondria with floral thermogenesis has been described, how mitochondrial dynamics are involved in the regulation of floral thermogenesis is unclear. In this study, the morphological and functional dynamics of mitochondria in vivo were assessed in Nelumbo nucifera Gaertn. flowers during floral thermogenesis. The results showed that mitochondrial biogenesis increased considerably in N. nucifera flowers during thermogenesis, accompanied by notable morphological changes in the mitochondria, including long elliptical, rod-shaped, and dumbbell-shaped morphologies, as well as increased mitochondrial reactive oxygen species (ROS) levels in TM cells. An increase in the expression of alternative oxidase (AOX) during the thermogenesis of N. nucifera flowers was also observed. These observations suggested the rapid change in mitochondrial morphology and increased density during thermogenesis implied activation of mitochondrial fission, which combined with elevated levels of mitochondrial ROS trigger a substantial increase in AOX within the respiratory pathway of TM N. nucifera.

Inhibition of Three Diabetes-Related Enzymes by Procyanidins from Lotus (Nelumbo nucifera Gaertn.) Seedpods

The inhibitory effects of procyanidins from lotus (Nelumbo nucifera Gaertn.) seedpods on the activities of α-amylase, α-glucosidase and protein tyrosine phosphatase 1B (PTP1B), were studied and compared with those of (+)-catechin, (-)-epicatechin, epigallocatechin gallate (EGCG), procyanidin dimer B2 and trimer C1. The results showed that Lotus procyanidin extract (LPE) significantly inhibited α-amylase, α-glucosidase and PTP1B with IC₅₀ values of 5.5, 1.0, and 0.33 μg/mL, respectively. The inhibition increased with the degree of polymerization and the existence of galloyl or gallocatechin units. Kinetic analysis showed that LPE inhibited α-glucosidase activity in a mixed competitive and noncompetitive mode. Fluorescence quenching revealed that α-glucosidase interacted with LPE or EGCG in an apparent static mode, or the model of "sphere of action". The apparent static (K) and bimolecular (k_q) constants were 4375 M^-1 and 4.375 × 10¹¹ M^-1 s^-1, respectively, for LPE and 1195 M^-1 and 1.195 × 10¹¹ M^-1 s^-1, respectively, for EGCG. Molecular docking analysis provided further information on the interactions of (+)-catechin, (-)-epicatechin, EGCG, B2 and C1 with α-glucosidase. It is hypothesized that LPE may bind to multiple sites of the enzyme through hydrogen bonding and hydrophobic interactions, leading to conformational changes in the enzyme and thus inhibiting its activity. These findings first elucidate the inhibitory effect of LPE on diabetes-related enzymes and highlight the usefulness of LPE as a dietary supplement for the prophylaxis of diabetes.

Hepatoprotective Activity of Nelumbo nucifera Gaertn. Seedpod Extract Attenuated Acetaminophen-Induced Hepatotoxicity

The aim is to investigate the effect of lotus (Nelumbo nucifera Gaertn.) seedpod extract (LSE) on acetaminophen (APAP)-induced hepatotoxicity. LSE is rich in polyphenols and has potent antioxidant capacity. APAP is a commonly used analgesic, while APAP overdose is the main reason for drug toxicity in the liver. Until now, there has been no in vitro test of LSE in drug-induced hepatotoxicity responses. LSEs were used to evaluate the effect on APAP-induced cytotoxicity, ROS level, apoptotic rate, and molecule mechanisms. The co-treatment of APAP and LSEs elevated the survival rate and decreased intracellular ROS levels on HepG2 cells. LSEs treatment could significantly reduce APAP-induced HepG2 apoptosis assessed by DAPI and Annexin V/PI. The further molecule mechanisms indicated that LSEs decreased Fas/FasL binding and reduced Bax and tBid to restore mitochondrial structure and subsequently suppress downstream apoptosis cascade activation. These declines in COX-2, NF-κB, and iNOS levels were observed in co-treatment APAP and LSEs, which indicated that LSEs could ameliorate APAP-induced inflammation. LSE protected APAP-induced apoptosis by preventing extrinsic, intrinsic, and JNK-mediated pathways. In addition, the restoration of mitochondria and inflammatory suppression in LSEs treatments indicated that LSEs could decrease oxidative stress induced by toxic APAP. Therefore, LSE could be a novel therapeutic option for an antidote against overdose of APAP.

Comparative analyses of American and Asian lotus genomes reveal insights into petal color, carpel thermogenesis and domestication

Nelumbo lutea (American lotus), which differs from Nelumbo nucifera (Asian lotus) morphologically, is one of the two remaining species in the basal eudicot family Nelumbonaceae. Here, we assembled the 843-Mb genome of American lotus into eight pseudochromosomes containing 31 382 protein-coding genes. Comparative analyses revealed conserved synteny without large chromosomal rearrangements between the genomes of American and Asian lotus and identified 29 533 structural variants (SVs). Carotenoid and anthocyanin pigments determine the yellow and red petal colors of American and Asian lotus, respectively. The structural genes encoding enzymes of the carotenoid and anthocyanin biosynthesis pathways were conserved between two species but differed in expression. We detected SVs caused by repetitive sequence expansion or contraction among the anthocyanin biosynthesis regulatory MYB genes. Further transient overexpression of candidate NnMYB5 induced anthocyanin accumulation in lotus petals. Alternative oxidase (AOX), uncoupling proteins (UCPs), and sugar metabolism and transportation contributed to carpel thermogenesis. Carpels produce heat with sugars transported from leaves as the main substrates, because there was weak tonoplast sugar transporter (TST) activity, and with SWEETs were highly expressed during thermogenesis. Cell proliferation-related activities were particularly enhanced in the warmer carpels compared with stamens during the cold night before blooming, which suggested that thermogenesis plays an important role in flower protogyny. Population genomic analyses revealed deep divergence between American and Asian lotus, and independent domestication affecting seed, rhizome, and flower traits. Our findings provide a high-quality reference genome of American lotus for exploring the genetic divergence and variation between two species and revealed possible genomic bases for petal color, carpel thermogenesis and domestication in lotus.

Color fading in lotus (Nelumbo nucifera) petals is manipulated both by anthocyanin biosynthesis reduction and active degradation

Flower color is a key trait that determines the ornamental quality of aquatic lotus (Nelumbo nucifera). Color fading significantly decreases the ornamental value of lotus flowers. However, the molecular mechanism underlying lotus petal discoloration remains largely unknown. Here, the anthocyanin content and global transcriptional profiling of lotus petals of cultivar 'Qiusanse' in four developmental stages were analyzed. Five anthocyanin components were detected, and the total anthocyanin content decreased as the petal color changed from red to nearly white. Moreover, the malondialdehyde (MDA) content and peroxidase (POD) activity increased during color fading. RNA-seq analysis revealed a total of 4,092 differentially expressed genes (DEGs) between petal developmental stages. Notably, oxidoreductase and hydrolase activity related genes were overrepresented in DEGs. The expression pattern of key anthocyanin biosynthesis genes including, CHS, F3H, ANS, UFGT, and transcription factor regulators, including MYBs, WRKYs and bHLHs were correlated with anthocyanin accumulation. Interestingly, DEGs associated with anthocyanin degradation and vacuolar pH regulation, including peroxidase, proton pumps regulators such as WRKY3 and MYB5-like, were significantly upregulated during the late stages of flowering. This study reveals for the first time the transcriptional dynamics during lotus petal discoloration. Our results suggest the involvement of anthocyanin biosynthesis repressors and degrading genes as well as pH regulators in controlling color fading of lotus petals. The study also provides valuable information and candidate genes for improving the lotus flower color.

Lignin Synthesis, Affected by Sucrose in Lotus (Nelumbo nucifera) Seedlings, Was Involved in Regulation of Root Formation in the Arabidopsis thanliana

Adventitious roots (ARs) have an unmatched status in plant growth and metabolism due to the degeneration of primary roots in lotuses. In the present study, we sought to assess the effect of sucrose on ARs formation and observed that lignin synthesis was involved in ARs development. We found that the lignification degree of the ARs primordium was weaker in plants treated with 20 g/L sucrose than in 50 g/L sucrose treatment and control plants. The contents of lignin were lower in plants treated with 20 g/L sucrose and higher in plants treated with 50 g/L sucrose. The precursors of monomer lignin, including p-coumaric acid, caffeate, sinapinal aldehyde, and ferulic acid, were lower in the GL50 library than in the GL20 library. Further analysis revealed that the gene expression of these four metabolites had no novel difference in the GL50/GL20 libraries. However, a laccase17 gene (NnLAC17), involved in polymer lignin synthesis, had a higher expression in the GL50 library than in the GL20 library. Therefore, NnLAC17 was cloned and the overexpression of NnLAC17 was found to directly result in a decrease in the root number in transgenic Arabidopsis plants. These findings suggest that lignin synthesis is probably involved in ARs formation in lotus seedlings.

Enzymatic basis for stepwise C-glycosylation in the formation of flavonoid di-C-glycosides in sacred lotus (Nelumbo nucifera Gaertn.)

Lotus plumule, the embryo of the seed of the sacred lotus (Nelumbo nucifera), contains a high accumulation of secondary metabolites including flavonoids and possesses important pharmaceutical value. Flavonoid C-glycosides, which accumulate exclusively in lotus plumule, have attracted considerable attention in recent decades due to their unique chemical structure and special bioactivities. As well as mono-C-glycosides, lotus plumule also accumulates various kinds of di-C-glycosides by mechanisms which are as yet unclear. In this study we identified two C-glycosyltransferase (CGT) genes by mining sacred lotus genome data and provide in vitro and in planta evidence that these two enzymes (NnCGT1 and NnCGT2, also designated as UGT708N1 and UGT708N2, respectively) exhibit CGT activity. Recombinant UGT708N1 and UGT708N2 can C-glycosylate 2-hydroxyflavanones and 2-hydroxynaringenin C-glucoside, forming flavone mono-C-glycosides and di-C-glycosides, respectively, after dehydration. In addition, the above reactions were successfully catalysed by cell-free extracts from tobacco leaves transiently expressing NnCGT1 or NnCGT2. Finally, enzyme assays using cell-free extracts of lotus plumule suggested that flavone di-C-glycosides (vicenin-1, vicenin-3, schaftoside and isoschaftoside) are biosynthesized through sequentially C-glucosylating and C-arabinosylating/C-xylosylating 2-hydroxynaringenin. Taken together, our results provide novel insights into the biosynthesis of flavonoid di-C-glycosides by proposing a new biosynthetic pathway for flavone C-glycosides in N. nucifera and identifying a novel uridine diphosphate-glycosyltransferase (UGT708N2) that specifically catalyses the second glycsosylation, C-arabinosylating and C-xylosylating 2-hydroxynaringenin C-glucoside.

A bHLH gene NnTT8 of Nelumbo nucifera regulates anthocyanin biosynthesis

Lotus is an important aquatic ornamental plant, whose flower color is one of the key horticultural traits that determines its ornamental value. Previous studies revealed that anthocyanins largely determined the red color of lotus flower, which are also the main component that has beneficial effects on human health. However, the regulation mechanism of flower pigmentation in lotus flower remains unclear. In the present study, in order to further understand the regulatory mechanism underlying the anthocyanin biosynthesis, a bHLH gene NnTT8 was characterized to be phylogenetically close to AtTT8 and the bHLH proteins from other plant species that have been indicated to be involved in the positive regulation of anthocyanin biosynthesis. Complementation analysis in Arabidopsis tt8 mutant showed that NnTT8 could function similarly to AtTT8 in regulating anthocyanin and proanthocyanin biosynthesis. An MYB transcription factor capable of interacting with NnTT8 was also characterized from lotus. The identification of a bHLH transcription factor playing regulatory roles in anthocyanin biosynthesis is crucial, as it might help to obtain more in-depth insight into the coloration of lotus and help in breeding high anthocyanin content lotus variety that can be explored for lotus flower beverages.

Integrated Omics Analyses Identify Key Pathways Involved in Petiole Rigidity Formation in Sacred Lotus

Sacred lotus (Nelumbo nucifera Gaertn.) is a relic aquatic plant with two types of leaves, which have distinct rigidity of petioles. Here we assess the difference from anatomic structure to the expression of genes and proteins in two petioles types, and identify key pathways involved in petiole rigidity formation in sacred lotus. Anatomically, great variation between the petioles of floating and vertical leaves were observed. The number of collenchyma cells and thickness of xylem vessel cell wall was higher in the initial vertical leaves’ petiole (IVP) compared to the initial floating leaves’ petiole (IFP). Among quantified transcripts and proteins, 1021 and 401 transcripts presented 2-fold expression increment (named DEGs, genes differentially expressed between IFP and IVP) in IFP and IVP, 421 and 483 proteins exhibited 1.5-fold expression increment (named DEPs, proteins differentially expressed between IFP and IVP) in IFP and IVP, respectively. Gene function and pathway enrichment analysis displayed that DEGs and DEPs were significantly enriched in cell wall biosynthesis and lignin biosynthesis. In consistent with genes and proteins expressions in lignin biosynthesis, the contents of lignin monomers precursors were significantly different in IFP and IVP. These results enable us to understand lotus petioles rigidity formation better and provide valuable candidate genes information on further investigation.

Small RNA and Transcriptome Sequencing Reveals miRNA Regulation of Floral Thermogenesis in Nelumbo nucifera

The sacred lotus (Nelumbo nucifera Gaertn.) can produce heat autonomously and maintain a relatively stable floral chamber temperature for several days when blooming. Floral thermogenesis is critical for flower organ development and reproductive success. However, the regulatory role of microRNA (miRNA) underlying floral thermogenesis in N. nucifera remains unclear. To comprehensively understand the miRNA regulatory mechanism of thermogenesis, we performed small RNA sequencing and transcriptome sequencing on receptacles from five different developmental stages. In the present study, a total of 172 known miRNAs belonging to 39 miRNA families and 126 novel miRNAs were identified. Twenty-nine thermogenesis-related miRNAs and 3024 thermogenesis-related mRNAs were screened based on their expression patterns. Of those, seventeen differentially expressed miRNAs (DEMs) and 1765 differentially expressed genes (DEGs) had higher expression during thermogenic stages. The upregulated genes in the thermogenic stages were mainly associated with mitochondrial function, oxidoreductase activity, and the energy metabolism process. Further analysis showed that miR156_2, miR395a_5, miR481d, and miR319p may play an important role in heat-producing activity by regulating cellular respiration-related genes. This study provides comprehensive miRNA and mRNA expression profile of receptacle during thermogenesis in N. nucifera, which advances our understanding on the regulation of floral thermogenesis mediated by miRNA.

Isolation and characterization of two O-methyltransferases involved in benzylisoquinoline alkaloid biosynthesis in sacred lotus (Nelumbo nucifera)

Benzylisoquinoline alkaloids (BIAs) are a major class of plant metabolites with many pharmacological benefits. Sacred lotus (Nelumbo nucifera) is an ancient aquatic plant of medicinal value because of antiviral and immunomodulatory activities linked to its constituent BIAs. Although more than 30 BIAs belonging to the 1-benzylisoquinoline, aporphine, and bisbenzylisoquinoline structural subclasses and displaying a predominant R-enantiomeric conformation have been isolated from N. nucifera, its BIA biosynthetic genes and enzymes remain unknown. Herein, we report the isolation and biochemical characterization of two O-methyltransferases (OMTs) involved in BIA biosynthesis in sacred lotus. Five homologous genes, designated NnOMT1-5 and encoding polypeptides sharing >40% amino acid sequence identity, were expressed in Escherichia coli Functional characterization of the purified recombinant proteins revealed that NnOMT1 is a regiospecific 1-benzylisoquinoline 6-O-methyltransferase (6OMT) accepting both R- and S-substrates, whereas NnOMT5 is mainly a 7-O-methyltransferase (7OMT), with relatively minor 6OMT activity and a strong stereospecific preference for S-enantiomers. Available aporphines were not accepted as substrates by either enzyme, suggesting that O-methylation precedes BIA formation from 1-benzylisoquinoline intermediates. Km values for NnOMT1 and NnOMT5 were 20 and 13 μm for (R,S)-norcoclaurine and (S)-N-methylcoclaurine, respectively, similar to those for OMTs from other BIA-producing plants. Organ-based correlations of alkaloid content, OMT activity in crude extracts, and OMT gene expression supported physiological roles for NnOMT1 and NnOMT5 in BIA metabolism, occurring primarily in young leaves and embryos of sacred lotus. In summary, our work identifies two OMTs involved in BIA metabolism in the medicinal plant N. nucifera.

Differences in flavonoid pathway metabolites and transcripts affect yellow petal colouration in the aquatic plant Nelumbo nucifera

BACKGROUND

The Asia lotus (Nelumbo nucifera Gaertn.) is an ornamental aquatic plant with high economic value. Flower colour is an important ornamental trait, with much of N. nucifera breeding focusing on its yellow flowers. To explore the yellow flower colouration mechanism in N. nucifera, we analysed its pigment constituents and content, as well as gene expression in the flavonoid pathway, in two N. nucifera cultivars.

RESULTS

We performed metabolomic and gene expression analyses in two N. nucifera cultivars with yellow and white flowers, Molinqiuse (MLQS) and Yeguangbei (YGB), respectively, at five stages of flower colouration. Based on phenotypic observation and metabolite analyses, the later stages of flower colouration (S3-S5) were determined to be key periods for differences between MLQS and YGB, with dihydroflavonols and flavonols differing significantly between cultivars. Dihydroquercetin, dihydrokaempferol, and isorhamnetin were significantly higher in MLQS than in YGB, whereas kaempferol was significantly higher in YGB. Most of the key homologous structural genes in the flavonoid pathway were significantly more active in MLQS than in YGB at stages S1-S4.

CONCLUSION

In this study, we performed the first analyses of primary and secondary N. nucifera metabolites during flower colouration, and found that isorhamnetin and kaempferol shunting resulted in petal colour differences between MLQS and YGB. Based on our data integration analyses of key enzyme expression in the putative flavonoid pathways of the two N. nucifera cultivars, NnFLS gene substrate specificity and differential expression of NnOMTs may be related to petal colour differences between MLQS and YGB. These results will contribute to determining the mechanism of yellow flower colouration in N. nucifera, and will improve yellow petal colour breeding in lotus species.

Benzylisoquinoline Alkaloids Biosynthesis in Sacred Lotus

Sacred lotus (Nelumbo nucifera Gaertn.) is an ancient aquatic plant used throughout Asia for its nutritional and medicinal properties. Benzylisoquinoline alkaloids (BIAs), mostly within the aporphine and bisbenzylisoquinoline structural categories, are among the main bioactive constituents in the plant. The alkaloids of sacred lotus exhibit promising anti-cancer, anti-arrhythmic, anti-HIV, and anti-malarial properties. Despite their pharmacological significance, BIA metabolism in this non-model plant has not been extensively investigated. In this review, we examine the diversity of BIAs in sacred lotus, with an emphasis on the distinctive stereochemistry of alkaloids found in this species. Additionally, we discuss our current understanding of the biosynthetic genes and enzymes involved in the formation of 1-benzylisoquinoline, aporphine, and bisbenzylisoquinoline alkaloids in the plant. We conclude that a comprehensive functional characterization of alkaloid biosynthetic enzymes using both in vitro and in vivo methods is required to advance our limited knowledge of BIA metabolism in the sacred lotus.

Evolutionarily conserved function of the sacred lotus (Nelumbo nucifera Gaertn.) CER2-LIKE family in very-long-chain fatty acid elongation

Identification of NnCER2 and NnCER2-LIKE from Nelumbo nucifera, which are required for the very-long-chain fatty acid elongation, provides new evidence that CER2 proteins are evolutionarily conserved across the eudicots. CER2-LIKE family proteins have been described as core components of the fatty acid elongase complex in Arabidopsis, maize, and rice, having specific function in synthesis of the C₃₀ to C₃₄ fatty acyl-CoA precursors of cuticular waxes. Little is known about the functional conservation in this gene family across species. In this study, two CER2-LIKE family proteins, NnCER2 and NnCER2-LIKE, were characterized from sacred lotus (Nelumbo nucifera), which is an ancient basal eudicot. The transcriptional expression of NnCER2 and NnCER2-LIKE was found in floating leaf blades, emergent petioles and vertical leaves, petals, and anthers. The NnCER2 and NnCER2-LIKE proteins were localized to the endoplasmic reticulum and nucleus. Overexpressing NnCER2 and NnCER2-LIKE in Arabidopsis led to alteration of cuticle wax structure in inflorescence stems, and this was associated with elevated 30, 32, and 34 carbon length wax compounds, and their derivatives. The different substrate specificities of NnCER2 and NnCER2-LIKE were explored using co-expression with AtCER6 in yeast cells. These findings provide clear evidence that the function of CER2 family proteins in producing VLCFAs is highly conserved across the eudicots.

Analysis of Isoquinoline Alkaloid Composition and Wound-Induced Variation in Nelumbo Using HPLC-MS/MS

Alkaloids are the most relevant bioactive components in lotus, a traditional herb in Asia, but little is known about their qualitative and quantitative distributions. Here, we report on the alkaloid composition in various lotus organs. Lotus laminae and embryos are rich in isoquinoline alkaloids, whereas petioles and rhizomes contain trace amounts of alkaloids. Wide variation of alkaloid accumulation in lamina and embryo was observed among screened genotypes. In laminae, alkaloid accumulation increases during early developmental stages, reaches the highest level at full size stage, and then decreases slightly during senescence. Vegetative and embryogenic tissues accumulate mainly aporphine-type and bisbenzylisoquinoline-type alkaloids, respectively. Bisbenzylisoquinoline-type alkaloids may be synthesized mainly in lamina and then transported into embryo via latex through phloem translocation. In addition, mechanical wounding was shown to induce significant accumulation of specific alkaloids in lotus leaves.

Cloning and expression of an APETALA1-like gene from Nelumbo nucifera

The objective of this study was to clone the full-length cDNA of the APETALA1 (AP1) gene from lotus and analyze its sequence and expression pattern. The full-length cDNA sequence of the NnAP1 gene was amplified from the petals of Nelumbo nucifera 'Hongxia' using RT-PCR and rapid amplification of cDNA ends. Bioinformatic methods were used to analyze the sequence characteristics of the gene. Quantitative real-time PCR methods were used to investigate the expression pattern of NnAP1 in various organs and during different developmental stages. The cloned full-length NnAP1 cDNA (GenBank accession No. KF361315) was 902 bp, containing a 795-bp open reading frame encoding 264 amino acids with a relative molecular mass of 30,288.4 and an isoelectric point of 9.13. NnAP1 had a MADS-box domain and a K-box domain, which is typical of the SQUA/AP1 gene family. A protein sequence identity search showed that NnAP1 was 75-96% similar to other plant AP1s. Phylogenetic tree analysis indicated that NnAP1 was very closely related to AP1 of Glycine max, suggesting that they shared the same protein ancestor. Quantitative real-time PCR analysis showed that NnAP1 was expressed in various organs during different developmental stages; it had the highest expression in blooming flowers and had trace expression in the young vegetative and flower senescence stages. Our analysis suggests that NnAP1 plays an important role in controlling floral meristem identity and floral organ formation.

Biogenesis of C-glycosyl flavones and profiling of flavonoid glycosides in lotus (Nelumbo nucifera)

Flavonoids in nine tissues of Nelumbo nucifera Gaertner were identified and quantified by high-performance liquid chromatography with diode array detector (HPLC-DAD) and HPLC-electrospray ionization-mass spectrometry (HPLC-ESI-MSn). Thirty-eight flavonoids were identified; eleven C-glycosides and five O-glycosides were discovered for the first time in N. nucifera. Most importantly, the C-glycosyl apigenin or luteolin detected in lotus plumules proved valuable for deep elucidation of flavonoid composition in lotus tissues and for further utilization as functional tea and medicine materials. Lotus leaves possessed the significantly highest amount of flavonoids (2.06E3±0.08 mg 100 g(-1) FW) and separating and purifying the bioactive compound, quercetin 3-O-glucuronide, from leaves showed great potential. In contrast, flavonoids in flower stalks, seed coats and kernels were extremely low. Simultaneously, the optimal picking time was confirmed by comparing the compound contents in five developmental phases. Finally, we proposed the putative flavonoid biosynthesis pathway in N. nucifera.

Phosphorus removal from domestic wastewater by Nelumbo nucifera Gaertn. and Cyperus alternifolius L

Domestic wastewater is a source of phosphorus contamination that causes eutrophication when it contaminates aquatic environments. Nelumbo nucifera Gaertn. and Cyperus alternifolius L. were applied for phosphorus removal from domestic wastewater. From the study, phosphorus in domestic wastewater was removed from the initial concentration of 1.038 ± 0.001 mgL(-1) to 0.094 ± 0.001 and 0.048 ± 0.004 mgL(-1) by N. nucifera and C. alternifolius, respectively, within 5 days. In addition, total Kjeldahl nitrogen (TKN) and chemical oxygen demand (COD) also decreased when wetland systems were applied the same as treatment with conventional method (chemical + activated sludge process). However, the plant removed TDS better than the conventional method. During 5 cycles of exposure, the two plants still survived and were healthy. The weight of plants increased after the experiment from 4060 ± 0.05 g to 4820 ± 0.17 g of N. nucifera, and from 4000 ± 0.00 g to 4600 ± 0.14 g of C. alternifolius. Phosphorus content also increased in both plants after the experiment. However, in the wetland system, phosphorus was removed mainly by the soil, followed by the plants, and then microorganisms. The domain group in the microbial community of both wetland systems was Pseudomas sp.

Stomata actively regulate internal aeration of the sacred lotus Nelumbo nucifera

The sacred lotus Nelumbo nucifera (Gaertn.) possesses a complex system of gas canals that channel pressurized air from its leaves, down through its petioles and rhizomes, before venting this air back to the atmosphere through large stomata found in the centre of every lotus leaf. These central plate stomata (CPS) lie over a gas canal junction that connects with two-thirds of the gas canals within the leaf blade and with the larger of two discrete pairs of gas canals within the petiole that join with those in the rhizome. It is hypothesized that the lotus actively regulates the pressure, direction and rate of airflow within its gas canals by opening and closing these stomata. Impression casting the CPS reveal that they are open in the morning, close at midday and reopen in the afternoon. The periodic closure of the CPS during the day coincides with a temporary reversal in airflow direction within the petiolar gas canals. Experiments show that the conductance of the CPS decreases in response to increasing light level. This behaviour ventilates the rhizome and possibly directs benthic CO2 towards photosynthesis in the leaves. These results demonstrate a novel function for stomata: the active regulation of convective airflow.

Isolation and functional characterization of a salt responsive transcriptional factor, LrbZIP from lotus root (Nelumbo nucifera Gaertn)

Basic leucine zipper transcription factor (bZIP) is involved in signaling transduction for various stress responses. Here we reported a bZIP transcription factor (accession: JX887153) isolated from a salt-resistant lotus root using cDNA-AFLP approach with RT-PCR and RACE-PCR method. Full-length cDNA which consisted of a single open reading frame encoded a putative polypeptide of 488 amino acids. On the basis of 78, 76, and 75 % sequence similarity with the bZIPs from Medicago truncatula (XP_003596814.1), Carica papaya (ABS01351.1) and Arabidopsis thaliana (NP_563810.2), we designed it as LrbZIP. Semi quantitative RT-PCR results, performed on the total RNA extracted from tips of lotus root, showed that LrbZIP expression was increased with 250 mM NaCl treatment for 18 h. Effects of low temperature on the expression of LrbZIP was also studied, and its expression was significantly enhanced with a 4 °C treatment for 12 h. In addition, LrbZIP expression was strongly induced by treatment with exogenous 100 μM ABA. To evaluate its function across the species, tobacco (Nicotiana tabacum L.) was transformed with LrbZIP in a binary vector construct. Transgenic plants exhibited higher resistance as compared with the control according to the results of the root growth, chlorophyll content and electrolyte leakage when exposed to NaCl treatment. In addition, LrCDPK2, LrLEA, and TPP also showed enhanced expression in the transgenic plants. Overall, expression of LrbZIP was probably very important for salt-resistant lotus root to survive through salt stress.

Simultaneous analysis of anthocyanin and non-anthocyanin flavonoid in various tissues of different lotus (Nelumbo) cultivars by HPLC-DAD-ESI-MS(n)

A validated HPLC-DAD-ESI-MS(n) method for the analysis of non-anthocyanin flavonoids was applied to nine different tissues of twelve lotus genotypes of Nelumbo nucifera and N. lutea, together with an optimized anthocyanin extraction and separation protocol for lotus petals. A total of five anthocyanins and twenty non-anthocyanin flavonoids was identified and quantified. Flavonoid contents and compositions varied with cultivar and tissue and were used as a basis to divide tissues into three groups characterized by kaempferol and quercetin derivatives. Influences on flower petal coloration were investigated by principal components analyses. High contents of kaempferol glycosides were detected in the petals of N. nucifera while high quercetin glycoside concentrations occurred in N. lutea. Based on these results, biosynthetic pathways leading to specific compounds in lotus tissues are deduced through metabolomic analysis of different genotypes and tissues and correlations among flavonoid compounds.

[Effects of aquatic plants during their decay and decomposition on water quality]

Taking 6 aquatic plant species as test objects, a 64-day decomposition experiment was conducted to study the temporal variation patterns of nutrient concentration in water body during the process of the aquatic plant decomposition. There existed greater differences in the decomposition rates between the 6 species. Floating-leaved plants had the highest decomposition rate, followed by submerged plants, and emerged plants. The effects of the aquatic plant species during their decomposition on water quality differed, which was related to the plant biomass density. During the decomposition of Phragmites australis, water body had the lowest concentrations of chemical oxygen demand, total nitrogen, and total phosphorus. In the late decomposition period of Zizania latifolia, the concentrations of water body chemical oxygen demand and total nitrogen increased, resulting in the deterioration of water quality. In the decomposition processes of Nymphoides peltatum and Nelumbo nucifera, the concentrations of water body chemical oxygen demand and total nitrogen were higher than those during the decomposition of other test plants. In contrast, during the decomposition of Potamogeton crispus and Myriophyllum verticillatum, water body had the highest concentrations of ammonium, nitrate, and total phosphorus. For a given plant species, the main water quality indices had the similar variation trends under different biomass densities. It was suggested that the existence of moderate plant residues could effectively promote the nitrogen and phosphorus cycles in water body, reduce its nitrate concentration to some extent, and decrease the water body nitrogen load.

Proteomic and functional analyses of Nelumbo nucifera annexins involved in seed thermotolerance and germination vigor

Annexins are multifunctional proteins characterized by their capacity to bind calcium ions and negatively charged lipids. Although there is increasing evidence implicating their importance in plant stress responses, their functions in seeds remain to be further studied. In this study, we identified a heat-induced annexin, NnANN1, from the embryonic axes of sacred lotus (Nelumbo nucifera Gaertn.) using comparative proteomics approach. Moreover, the expression of NnANN1 increased considerably in response to high-temperature treatment. Quantitative real-time PCR (qRT-PCR) revealed that the transcripts of NnANN1 were detected predominantly during seed development and germination in sacred lotus, implicating a role for NnANN1 in plant seeds. Ectopic expression of NnANN1 in Arabidopsis resulted in enhanced tolerance to heat stress in transgenic seeds. In addition, compared to the wild-type seeds, transgenic seeds ectopically expressing NnANN1 exhibited improved resistance to accelerated aging treatment used for assessing seed vigor. Furthermore, transgenic seeds showed enhanced peroxidase activities, accompanied with reduced lipid peroxidation and reduced ROS release levels compared to the wild-type seeds. Taken together, these results indicate that NnANN1 plays an important role in seed thermotolerance and germination vigor.

Overexpression of Nelumbo nucifera metallothioneins 2a and 3 enhances seed germination vigor in Arabidopsis

Metallothioneins (MTs) are small, cysteine-rich and metal-binding proteins which are involved in metal homeostasis and scavenging of reactive oxygen species. Although plant MTs have been intensively studied, their roles in seeds remain to be clearly established. Here, we report the isolation and characterization of NnMT2a, NnMT2b and NnMT3 from sacred lotus (Nelumbo nucifera Gaertn.) and their roles in seed germination vigor. The transcripts of NnMT2a, NnMT2b and NnMT3 were highly expressed in developing and germinating sacred lotus seeds, and were dramatically up-regulated in response to high salinity, oxidative stresses and heavy metals. Analysis of transformed Arabidopsis protoplasts showed that NnMT2a-YFP and NnMT3-YFP were localized in cytoplasm and nucleoplasm. Transgenic Arabidopsis seeds overexpressing NnMT2a and NnMT3 displayed improved resistance to accelerated aging (AA) treatment, indicating their significant roles in seed germination vigor. These transgenic seeds also exhibited higher superoxide dismutase activity compared to wild-type seeds after AA treatment. In addition, we showed that NnMT2a and NnMT3 conferred improved germination ability to NaCl and methyl viologen on transgenic Arabidopsis seeds. Taken together, these data demonstrate that overexpression of NnMT2a and NnMT3 in Arabidopsis significantly enhances seed germination vigor after AA treatment and under abiotic stresses.

[Inhibitory effects of liquor cultured with Nelumbo nucifera and Nymphaea tetragona on the growth of Microcystis aeruginosa]

The inhibitory effects of liquor cultured with Nelumbo nucifera and Nymphaea tetragona on the growth of Microcystis aeruginosa have been investigated by measuring the cell number and the chlorophyll a content of Microcystis aeruginosa of culture in the laboratory. The results showed that the inhibitory effects on the growth of Microcystis aeruginosa with different concentration of the liquor cultured with Nelumbo nucifera and Nymphaea tetragona were dissimilar, and an evident phenomenon appeared that low concentrations could promote the growth of Microcystis aeruginosa. However, the inhibitory effects on the growth of Microcystis aeruginosa with continuous liquor cultured with Nelumbo nucifera and Nymphaea tetragona were obvious, which made the algal cell almost lose the capability of photosynthesis, and the inhibitory effects of liquor cultured with Nymphaea tetragona were better than those of Nelumbo nucifera. The scale-up experiment demonstrated that the algal cell received menace and damage by measuring the activities of peroxidase (SOD) and the accumulated contents of malondialdehyde (MDA) of Microcystis aeruginosa in the co-culture. Sterilization methods influenced the algal growth inhibition experiment so that high temperature couldn't replace micropore filter, which explained that the matter excreted by Nelumbo nucifera and Nymphaea tetragona may contain thermally-instabe matter.

Contribution of the alternative pathway to respiration during thermogenesis in flowers of the sacred lotus

We report results from in vivo measurements, using oxygen isotope discrimination techniques, of fluxes through the alternative and cytochrome respiratory pathways in thermogenic plant tissue, the floral receptacle of the sacred lotus (Nelumbo nucifera). Fluxes through both pathways were measured in thermoregulating flowers undergoing varying degrees of thermogenesis in response to ambient temperature. Significant increases in alternative pathway flux were found in lotus receptacles with temperatures 16 degrees C to 20 degrees C above ambient, but not in those with lesser amounts of heating. Alternative pathway flux in the hottest receptacles was 75% of the total respiratory flux. In contrast, fluxes through the cytochrome pathway did not change significantly during thermogenesis. These data support the hypothesis that increased flux through the alternative pathway is responsible for heating in the lotus and that it is unlikely that uncoupling proteins, which would have produced increased fluxes through the cytochrome pathway, contribute significantly to heating in this tissue. Comparisons of actual flux, with capacity determined using inhibitors, suggested that the alternative pathway was operating at close to maximum capacity in heating tissues of lotus. However, in nonheating tissues the inhibitor data significantly overestimated the alternative pathway flux. This confirms that isotopic measurements are necessary for accurate determination of fluxes through the two pathways.

Herpes simplex virus type 1 propagation in HeLa cells interrupted by Nelumbo nucifera

Inhibitory effects of ethanolic extracts from 10 Chinese herbs on herpes simplex virus type 1 (HSV-1) replication were investigated. By a bioassay-guided fractionation procedure, NN-B-5 was identified from seeds of N. nucifera. NN-B-5 significantly blocked HSV-1 multiplication in HeLa cells without apparent cytotoxicity. To elucidate the point in HSV-1 replication where arrest occurred, a set of key regulatory events leading to the viral multiplication was examined, including HSV-1 DNA synthesis and viral immediate early gene expressions. Data from polymerase chain reaction and Southern blotting showed that there were impairments of HSV-1 DNA replication in HeLa cells treated with NN-B-5. Results indicated that the production and mRNA transcription of infected cell protein (ICP) 0 and ICP4 were decreased in NN-B-5 treated HeLa cells. Results of an electrophoretic mobility shift assay demonstrated that NN-B-5 interrupted the formation of alpha-trans-induction factor/C1/Oct-1/GARAT multiprotein/DNA complexes. The mechanisms of antiviral action of NN-B-5 seem to be mediated, at least in part, through inhibition of immediate early transcripts, such as ICP0 and ICP4 mRNA and then blocking of all downstream viral products accumulation and progeny HSV-1 production.