Molecular characterization of maize acetylcholinesterase: a novel enzyme family in the plant kingdom

Genome-wide identification of the GDSL-type esterase/lipase protein (GELP) gene family in Ricinus communis and its transcriptional regulation during germination and seedling establishment under different abiotic stresses

GDSL-type esterase/lipase protein (GELP) genes are crucial in the specialized lipid metabolism, in the responses to abiotic stresses, and in the regulation of plant homeostasis. R. communis is an important oilseed crop species that can sustain growth and productivity when exposed to harsh environmental conditions. Herein, we raised the question of whether the GELP gene family could be involved in the acquisition of R. communis tolerance to abiotic stresses during seed germination and seedling establishment. Thus, we used bioinformatics and transcriptomics to characterize the R. communis GELP gene family. R. communis genome possesses 96 GELP genes that were characterized by extensive bioinformatics, including phylogenetic analysis, subcellular localization, exon-intron distribution, the analysis of regulatory cis-elements, tandem duplication, and physicochemical properties. Transcriptomics indicated that numerous RcGELP genes are readily responsive to high-temperature and salt stresses and might be potential candidates for genome editing techniques to develop abiotic stress-tolerant crops.

Role of acetylcholine and acetylcholinesterase in improving abiotic stress resistance/tolerance

Abiotic stress that plants face may impact their growth and limit their productivity. In response to abiotic stress, several endogenous survival mechanisms get activated, including the synthesis of quaternary amines in plants. Acetylcholine (ACh), a well-known quaternary amine, and its components associated with cholinergic signaling are known to contribute to a variety of physiological functions. However, their role under abiotic stress is not well documented. Even after several studies, there is a lack of a comprehensive understanding of how cholinergic components mitigate abiotic stress in plants. Acetylcholine hydrolyzing enzyme acetylcholinesterase (AChE) belongs to the GDSL lipase/acylhydrolase protein family and has been found in several plant species. Several studies have demonstrated that GDSL members are involved in growth, development, and abiotic stress. This review summarizes all the possible mitigating effects of the ACh-AChE system on abiotic stress tolerance and will try to highlight all the progress made so far in this field.

Contributions of Non-Neuronal Cholinergic Systems to the Regulation of Immune Cell Function, Highlighting the Role of α7 Nicotinic Acetylcholine Receptors

Loewi's discovery of acetylcholine (ACh) release from the frog vagus nerve and the discovery by Dale and Dudley of ACh in ox spleen led to the demonstration of chemical transmission of nerve impulses. ACh is now well-known to function as a neurotransmitter. However, advances in the techniques for ACh detection have led to its discovery in many lifeforms lacking a nervous system, including eubacteria, archaea, fungi, and plants. Notably, mRNAs encoding choline acetyltransferase and muscarinic and nicotinic ACh receptors (nAChRs) have been found in uninnervated mammalian cells, including immune cells, keratinocytes, vascular endothelial cells, cardiac myocytes, respiratory, and digestive epithelial cells. It thus appears that non-neuronal cholinergic systems are expressed in a variety of mammalian cells, and that ACh should now be recognized not only as a neurotransmitter, but also as a local regulator of non-neuronal cholinergic systems. Here, we discuss the role of non-neuronal cholinergic systems, with a focus on immune cells. A current focus of much research on non-neuronal cholinergic systems in immune cells is α7 nAChRs, as these receptors expressed on macrophages and T cells are involved in regulating inflammatory and immune responses. This makes α7 nAChRs an attractive potential therapeutic target.

Exploring the Evolvability of Plant Specialized Metabolism: Uniqueness Out Of Uniformity and Uniqueness Behind Uniformity

The huge structural diversity exhibited by plant specialized metabolites has primarily been considered to result from the catalytic specificity of their biosynthetic enzymes. Accordingly, enzyme gene multiplication and functional differentiation through spontaneous mutations have been established as the molecular mechanisms that drive metabolic evolution. Nevertheless, how plants have assembled and maintained such metabolic enzyme genes and the typical clusters that are observed in plant genomes, as well as why identical specialized metabolites often exist in phylogenetically remote lineages, is currently only poorly explained by a concept known as convergent evolution. Here, we compile recent knowledge on the co-presence of metabolic modules that are common in the plant kingdom but have evolved under specific historical and contextual constraints defined by the physicochemical properties of each plant specialized metabolite and the genetic presets of the biosynthetic genes. Furthermore, we discuss a common manner to generate uncommon metabolites (uniqueness out of uniformity) and an uncommon manner to generate common metabolites (uniqueness behind uniformity). This review describes the emerging aspects of the evolvability of plant specialized metabolism that underlie the vast structural diversity of plant specialized metabolites in nature.

Acetylation of amines and alcohols catalyzed by acetylcholinesterase from Pseudomonas aeruginosa PAO1

Acetylcholinesterase (AChE) from Pseudomonas aeruginosa PAO1 has a catalytic Ser residue in its active site. In this study, we examined the aminolysis and alcoholysis reactions of AChE that occurred alongside its hydrolysis reaction. The recombinant AChE recognized ethyl acetate as a substrate. Therefore, we evaluated acetylation of the amine and hydroxyl group by AChE, using acetylcholine and ethyl acetate as the acetyl donor. AChE recognized diaminoalkanes with 4- to 12-carbon chains and aminoalcohols with 4- to 8-carbon chains as acetyl acceptors, resulting in their acetylated products. In the acetylation of 1,6-diaminohexane, AChE preferentially used ethyl acetate as the acetyl donor above pH 8.0 and the efficiency increased with increasing pH. In contrast, the acetylation of 6-amino-1-hexanol was efficient with acetylcholine as the acetyl donor in the pH range of 4-10. In addition, acetylated 6-amino-1-hexanol was decomposed by AChE. The kinetic study indicated that the acetyl donor and acceptor are competitively recognized by AChE as substrates.

Metabolites That Confirm Induction and Release of Dormancy Phases in Sweet Cherry Buds

Here we report on metabolites found in a targeted profiling of 'Summit' flower buds for nine years, which could be indicators for the timing of endodormancy release (t₁) and beginning of ontogenetic development (t₁*). Investigated metabolites included chrysin, arabonic acid, pentose acid, sucrose, abscisic acid (ABA), and abscisic acid glucose ester (ABA-GE). Chrysin and water content showed an almost parallel course between leaf fall and t₁*. After 'swollen bud', water content raised from ~60 to ~80% at open cluster, while chrysin content decreased and lost its function as an acetylcholinesterase inhibitor. Both parameters can be suitable indicators for t₁*. Arabonic acid showed a clear increase after t₁*. Pentose acid would be a suitable metabolite to identify t₁ and t₁*, but would not allow describing the ecodormancy phase, because of its continuously low value during this time. Sucrose reached a maximum during ecodormancy and showed a significant correlation with air temperature, which confirms its cryoprotective role in this phase. The ABA content showed maximum values during endodormancy and decreased during ecodormancy, reaching 50% of its content t₁ at t₁*. It appears to be the key metabolite to define the ecodormancy phase. The ABA-GE was present at all stages and phases and was much higher than the ABA content and is a readily available storage pool in cherry buds.

Genome-Wide Classification and Phylogenetic Analyses of the GDSL-Type Esterase/Lipase (GELP) Family in Flowering Plants

GDSL-type esterase/lipase (GELP) enzymes have key functions in plants, such as developmental processes, anther and pollen development, and responses to biotic and abiotic stresses. Genes that encode GELP belong to a complex and large gene family, ranging from tens to more than hundreds of members per plant species. To facilitate functional transfer between them, we conducted a genome-wide classification of GELP in 46 plant species. First, we applied an iterative phylogenetic method using a selected set of representative angiosperm genomes (three monocots and five dicots) and identified 10 main clusters, subdivided into 44 orthogroups (OGs). An expert curation for gene structures, orthogroup composition, and functional annotation was made based on a literature review. Then, using the HMM profiles as seeds, we expanded the classification to 46 plant species. Our results revealed the variable evolutionary dynamics between OGs in which some expanded, mostly through tandem duplications, while others were maintained as single copies. Among these, dicot-specific clusters and specific amplifications in monocots and wheat were characterized. This approach, by combining manual curation and automatic identification, was effective in characterizing a large gene family, allowing the establishment of a classification framework for gene function transfer and a better understanding of the evolutionary history of GELP.

An amino acid transporter-like protein (OsATL15) facilitates the systematic distribution of thiamethoxam in rice for controlling the brown planthopper

Characterization and genetic engineering of plant transporters involved in the pesticide uptake and translocation facilitate pesticide relocation to the tissue where the pests feed, thus improving the bioavailability of the agrichemicals. We aimed to identify thiamethoxam (THX) transporters in rice and modify their expression for better brown planthopper (BPH) control with less pesticide application. A yeast library expressing 1385 rice transporters was screened, leading to the identification of an amino acid transporter-like (ATL) gene, namely OsATL15, which facilitates THX uptake in both yeast cells and rice seedlings. In contrast to a decrease in THX content in osatl15 knockout mutants, ectopic expression of OsATL15 under the control of the CaMV 35S promoter or a vascular-bundle-specific promoter gdcsPpro significantly increased THX accumulation in rice plants, thus further enhancing the THX efficacy against BPH. OsATL15 was localized in rice cell membrane and abundant in the root transverse sections, vascular bundles of leaf blade, and stem longitudinal sections, but not in hull and brown rice at filling stages. Our study shows that OsATL15 plays an essential role in THX uptake and its systemic distribution in rice. OsATL15 could be valuable in achieving precise pest control by biotechnology approaches.

Identification and molecular characterization of propionylcholinesterase, a novel pseudocholinesterase in rice

Cholinesterase is consisting of acetylcholinesterase (AChE) and pseudocholinesterase in vertebrates and invertebrates. AChE gene has been identified in several plant species, while pseudocholinesterase gene has not yet been found in any plant species. In this study, we report that the AChE gene paralog encodes propionylcholinesterase (PChE), a pseudocholinesterase in rice. PChE was found to be located adjacent to AChE (Os07g0586200) on rice chromosome 7 and designated as Os07g0586100. Phylogenetic tree analysis showed a close relationship between rice AChE and PChE. PChE-overexpressing rice had higher hydrolytic activity toward propionylthiocholine than acetylthiocholine and showed extremely low activity against butyrylthiocholine. Therefore, the PChE gene product was characterized as a propionylcholinesterase, a pseudocholinesterase. The rice PChE displayed lower sensitivity to the cholinesterase inhibitor, neostigmine bromide, than electric eel, maize, and rice AChEs. The recombinant PChE functions as a 171 kDa homotetramer. PChE was expressed during the later developmental stage, and it was found be localized in the extracellular spaces of the rice leaf tissue. These results suggest that the rice plant possesses PChE, which functions in the extracellular spaces at a later developmental stage. To the best of our knowledge, this study provides the first direct evidence and molecular characterization of PChE in plants.

Comparative transcriptome analysis reveals the regulatory effects of acetylcholine on salt tolerance of Nicotiana benthamiana

Salinity is a major cause of crop losses worldwide. Acetylcholine (ACh) can ameliorate the adverse effects of abiotic stresses on plant growth, including salinity stress; however, the underlying molecular mechanisms of this process are unclear. Here, seedlings of Nicotiana benthamiana grown under normal conditions or exposed to 150 mmol L-1 NaCl salinity stress were then treated with a root application of 10 μM ACh. Exogenous ACh application resulted in the downregulation of the activity of the antioxidant enzymes, ascorbate peroxidase, and catalase. ACh-treated plants had lower levels of reactive oxygen species, including the superoxide anion radical and hydrogen peroxide. Transcriptome analysis indicated that ACh treatment under salt stress promoted the differential expression of 658 genes in leaves of N. benthamiana (527 were upregulated and 131 were downregulated). Gene ontology enrichment and Kyoto Encyclopedia of Genes and Genomes pathway analyses revealed that exogenous ACh application was associated with a substantial increase in the transcripts of genes related to cell wall peroxidases, xyloglucan endotransglucosylases or hydrolases, and expansins, indicating that ACh activates cell wall biosynthesis in salt-stressed plants. ACh also enhanced the expression of genes associated with the auxin, gibberellin, brassinosteroid, and salicylic acid signalling pathways, indicating that ACh induces the activation of these pathways under salt stress. Collectively, these findings indicate that ACh-induced salt tolerance in N. benthamiana seedlings is mediated by the inhibition of antioxidant enzymes, activation of cell wall biosynthesis, and hormone signalling pathways. Stress-induced genes involved in osmotic regulation and oxidation resistance were induced by ACh under salt stress. The genes whose transcript levels were elevated by ACh treatment in salt-stressed N. benthamiana could be used as molecular markers of the physiological status of plants under salt stress.

Acetylcholine ameliorates the adverse effects of cadmium stress through mediating growth, photosynthetic activity and subcellular distribution of cadmium in tobacco (Nicotiana benthamiana)

Acetylcholine (ACh), a well-known major neurotransmitter, plays a potential role in response to abiotic stresses. However, the mechanism of ACh-mediated cadmium (Cd) toxicity in tobacco seedlings is largely uncharacterized. In this study, a hydroponics experiment was conducted under 100 μM Cd stress in the presence or absence of ACh (50 μM) to investigate the potential effects of ACh on Cd toxicity. The results revealed that ACh application effectively alleviated Cd-induced reductions in plant growth, photosynthetic pigments and gas exchange attributes and improved the photosystem II activity. Ultrastructural observation indicated that Cd exposure ruptured the internal structure of chloroplasts, and even caused the accumulation of osmiophilic granules in chloroplasts, whereas these phenomena were alleviated by the addition of ACh. Cd stress also caused a marked increase in oxidative stress, as evidenced by the accumulation of O2- and H2O2, which were efficiently minimized after ACh application by up-regulating antioxidant enzyme activities (superoxide dismutase, SOD; catalase, CAT; ascorbate peroxidase, APX; glutathione reductase, GR). Besides, Cd stress considerably increased the levels of glutathione (GSH), Non-protein thiols (NPTs) and phytochelatins (PCs), whereas ACh application to Cd-stressed seedlings further increased those contents, thereby enhancing the tolerance of Cd-stressed plants. Moreover, exogenously applied ACh declined the accumulation of Cd and minimized the damage from Cd toxicity by modulating the distribution of Cd in the vacuole and cell wall. Therefore, these results provide insights into the ameliorative effects of ACh on Cd-induced a series of physiological reactions.

Beneficial role of acetylcholine in chlorophyll metabolism and photosynthetic gas exchange in Nicotiana benthamiana seedlings under salinity stress

Acetylcholine (ACh) is believed to improve plant growth. However, regulation at biochemical and molecular levels is largely unknown. The present study investigated the impact of exogenously applied ACh (10 µm) on growth and chlorophyll metabolism in hydroponically grown Nicotiana benthamiana under salt stress (150 mm NaCl). Salinity reduced root hydraulic conductivity while ACh-treated seedlings exhibited a significant increase, resulting in increased relative water content. Salinity induced a reduction in chlorophyll biosynthetic intermediates, such as protoporphyrin-IX, Mg-photoporphyrin-IX and protochlorophyllide, which were significantly ameliorated in the presence of ACh. This influence of ACh on chlorophyll synthesis was confirmed by up-regulation of HEMA1, CHLH, CAO and POR genes. Gas exchange parameters, i.e. stomatal conductance, internal CO2 concentration and transpiration rate, increased with ACh, thereby alleviating the salinity effects on photosynthesis. In addition, the salinity-induced enhancement of lipid peroxidation declined after ACh treatment through modulation of the activity of the assayed antioxidant enzymes (superoxide dismutase and peroxidase). Importantly, ACh significantly reduced the uptake of Na and increased uptake of K, resulting in a decline in the Na/K ratio. Results of the present study indicate that ACh can be effective in ameliorating NaCl-induced osmotic stress, altering chlorophyll metabolism and thus photosynthesis by maintaining ion homeostasis, hydraulic conductivity and water balance.

Metabolite signatures of grasspea suspension-cultured cells illustrate the complexity of dehydration response

This represents the first report deciphering the dehydration response of suspension-cultured cells of a crop species, highlighting unique and shared pathways, and adaptive mechanisms via profiling of 330 metabolites. Grasspea, being a hardy legume, is an ideal model system to study stress tolerance mechanisms in plants. In this study, we investigated the dehydration-responsive metabolome in grasspea suspension-cultured cells (SCCs) to identify the unique and shared metabolites crucial in imparting dehydration tolerance. To reveal the dehydration-induced metabolite signatures, SCCs of grasspea were exposed to 10% PEG, followed by metabolomic profiling. Chromatographic separation by HPLC coupled with MRM-MS led to the identification of 330 metabolites, designated dehydration-responsive metabolites (DRMs), which belonged to 28 varied functional classes. The metabolome was found to be constituted by carboxylic acids (17%), amino acids (13.5%), flavonoids (10.9%) and plant growth regulators (10%), among others. Pathway enrichment analysis revealed predominance of metabolites involved in phytohormone biosynthesis, secondary metabolism and osmotic adjustment. Exogenous application of DRMs, arbutin and acetylcholine, displayed improved physiological status in stress-resilient grasspea as well as hypersensitive pea, while administration of lauric acid imparted detrimental effects. This represents the first report on stress-induced metabolomic landscape of a crop species via a suspension culture system, which would provide new insights into the molecular mechanism of stress responses and adaptation in crop species.

Characterization and kinetic study of the brain and muscle acetylcholinesterase from Danio rerio

Acetylcholinesterase (AChE) plays an important role in the therapy of Alzheimer's disease and in the detection of pesticides such as organophosphates which are also widely used in chemical warfare. The aim of this study is the physicochemical and kinetic characterization of brain and muscle ChE from Danio rerio (Zebrafish). Optimal activity was found for brain ChE at alkaline pH 9.0 at 30 °C, and for muscle ChE at alkaline pH 8.5 at temperatures between 20 °C and 35 °C. The apparent kinetic constants, K_m^app and V_max^app, for brain ChE were determined as 0.191 ± 0.024 mM and 0.566 ± 0.028 U/mg protein, and for muscle ChE as 0.230 ± 0.030 mM and 0.677 ± 0.039 U/mg protein. Both brain and muscle ChE showed inhibition at high substrate concentrations. Brain and muscle ChE showed IC50 values for physostigmine of 0.61 μM and 0.37 μM, respectively. The ChE activity in brain was significantly inhibited by BW254c51 in all concentrations tested, but not by Iso-OMPA, while muscle ChE presented a moderate decrease (13 to 29%) in the activity values, indicating that BuChE is present.

Ohm R, Drobne D, Jemec Kokalj A. First evidence of cholinesterase-like activity in Basidiomycota

Cholinesterases (ChE), the enzymes whose primary function is the hydrolysis of choline esters, are widely expressed throughout the nature. Although they have already been found in plants and microorganisms, including ascomycete fungi, this study is the first report of ChE-like activity in fungi of the phylum Basidiomycota. This activity was detected in almost a quarter of the 45 tested aqueous fungal extracts. The ability of these extracts to hydrolyse acetylthiocholine was about ten times stronger than the hydrolytic activity towards butyrylthiocholine and propionylthiocholine. In-gel detection of ChE-like activity with acetylthiocholine indicated a great variability in the characteristics of these enzymes which are not characterized as vertebrate-like based on (i) differences in inhibition by excess substrate, (ii) susceptibility to different vertebrate acetylcholinesterase and butyrylcholinesterase inhibitors, and (iii) a lack of orthologs using phylogenetic analysis. Limited inhibition by single inhibitors and multiple activity bands using in-gel detection indicate the presence of several ChE-like enzymes in these aqueous extracts. We also observed inhibitory activity of the same aqueous mushroom extracts against insect acetylcholinesterase in 10 of the 45 samples tested; activity was independent of the presence of ChE-like activity in extracts. Both ChE-like activities with different substrates and the ability of extracts to inhibit insect acetylcholinesterase were not restricted to any fungal family but were rather present across all included Basidiomycota families. This study can serve as a platform for further research regarding ChE activity in mushrooms.

Differential Expression of Cholinergic System Components in Human Induced Pluripotent Stem Cells, Bone Marrow-Derived Multipotent Stromal Cells, and Induced Pluripotent Stem Cell-Derived Multipotent Stromal Cells

The components of the cholinergic system are evolutionary very old and conserved molecules that are expressed in typical spatiotemporal patterns. They are involved in signaling in the nervous system, whereas their functions in nonneuronal tissues are hardly understood. Stem cells present an attractive cellular system to address functional issues. This study therefore compared human induced pluripotent stem cells (iPSCs; from cord blood endothelial cells), mesenchymal stromal cells derived from iPSCs (iPSC-MSCs), and bone marrow-derived MSCs (BM-MSCs) from up to 33 different human donors with respect to gene expressions of components of the cholinergic system. The status of cells was identified and characterized by the detection of cell surface antigens using flow cytometry. Acetylcholinesterase expression in iPSCs declined during their differentiation into MSCs and was comparably low in BM-MSCs. Butyrylcholinesterase was present in iPSCs, increased upon transition from the three-dimensional embryoid body phase into monolayer culture, and declined upon further differentiation into iPSC-MSCs. In BM-MSCs a notable butyrylcholinesterase expression could be detected in only four donors, but was elusive in other patient-derived samples. Different nicotinic acetylcholine receptor subunits were preferentially expressed in iPSCs and during early differentiation into iPSC-MSCs, low expression was detected in iPS-MSCs and in BM-MSCs. The m2 and m3 variants of muscarinic acetylcholine receptors were detected in all stem cell populations. In BM-MSCs, these gene expressions varied between donors. Together, these data reveal the differential expression of cholinergic signaling system components in stem cells from specific sources and suggest the utility of our approach to establish informative biomarkers.

Efforts toward treatments against aging of organophosphorus-inhibited acetylcholinesterase

Aging is a dealkylation reaction of organophosphorus (OP)-inhibited acetylcholinesterase (AChE). Despite many studies to date, aged AChE cannot be reactivated directly by traditional pyridinium oximes. This review summarizes strategies that are potentially valuable in the treatment against aging in OP poisoning. Among them, retardation of aging seeks to lower the rate of aging through the use of AChE effectors. These drugs should be administered before AChE is completely aged. For postaging treatment, realkylation of aged AChE by appropriate alkylators may pave the way for oxime treatment by neutralizing the oxyanion at the active site of aged AChE. The other two strategies, upregulation of AChE expression and introduction of exogenous AChE, cannot resurrect aged AChE but may compensate for lowered active AChE levels by in situ production or external introduction of active AChE. Upregulation of AChE expression can be triggered by some peptides. Sources of exogenous AChE can be whole blood or purified AChE, either from human or nonhuman species.

New Trends and Perspectives in the Evolution of Neurotransmitters in Microbial, Plant, and Animal Cells

The evolutionary perspective on the universal roles of compounds known as neurotransmitters may help in the analysis of relations between all organisms in biocenosis-from microorganisms to plant and animals. This phenomenon, significant for chemosignaling and cellular endocrinology, has been important in human health and the ability to cause disease or immunity, because the "living environment" influences every organism in a biocenosis relationship (microorganism-microorganism, microorganism-plant, microorganism-animal, plant-animal, plant-plant and animal-animal). Non-nervous functions of neurotransmitters (rather "biomediators" on a cellular level) are considered in this review and ample consideration is given to similarities and differences that unite, as well as distinguish, taxonomical kingdoms.

The Pollen Coat Proteome: At the Cutting Edge of Plant Reproduction

The tapetum is a single layer of secretory cells which encloses the anther locule and sustains pollen development and maturation. Upon apoptosis, the remnants of the tapetal cells, consisting mostly of lipids and proteins, fill the pits of the sculpted exine to form the bulk of the pollen coat. This extracellular matrix forms an impermeable barrier that protects the male gametophyte from water loss and UV light. It also aids pollen adhesion and hydration and retains small signaling compounds involved in pollen-stigma communication. In this study, we have updated the list of the pollen coat's protein components and also discussed their functions in the context of sexual reproduction.

Altered expression of acetylcholinesterase gene in rice results in enhancement or suppression of shoot gravitropism

Acetylcholinesterase (AChE), an acetylcholine-hydrolyzing enzyme, exists widely in plants, although its role in plant signal transduction is still unclear. We have hypothesized that the plant AChE regulates asymmetric distribution of hormones and substrates due to gravity stimulus, based on indirect pharmacological experiments using an AChE inhibitor. As a direct evidence for this hypothesis, our recent study has shown that AChE overexpression causes an enhanced gravitropic response in rice seedlings and suggested that the function of the rice AChE relates to the promotion of shoot gravitropism in the seedlings. Here, we report that AChE suppression inhibited shoot gravitropism in rice seedlings, as supportive evidence demonstrating the role of AChE as a positive regulator of shoot gravitropic response in plants.

Overexpression of acetylcholinesterase gene in rice results in enhancement of shoot gravitropism

Acetylcholine (ACh), a known neurotransmitter in animals and acetylcholinesterase (AChE) exists widely in plants, although its role in plant signal transduction is unclear. We previously reported AChE in Zea mays L. might be related to gravitropism based on pharmacological study using an AChE inhibitor. Here we clearly demonstrate plant AChE play an important role as a positive regulator in the gravity response of plants based on a genetic study. First, the gene encoding a second component of the ACh-mediated signal transduction system, AChE was cloned from rice, Oryza sativa L. ssp. Japonica cv. Nipponbare. The rice AChE shared high homology with maize, siratro and Salicornia AChEs. Similar to animal and other plant AChEs, the rice AChE hydrolyzed acetylthiocholine and propionylthiocholine, but not butyrylthiocholine. Thus, the rice AChE might be characterized as an AChE (E.C.3.1.1.7). Similar to maize and siratro AChEs, the rice AChE exhibited low sensitivity to the AChE inhibitor, neostigmine bromide, compared with the electric eel AChE. Next, the functionality of rice AChE was proved by overexpression in rice plants. The rice AChE was localized in extracellular spaces of rice plants. Further, the rice AChE mRNA and its activity were mainly detected during early developmental stages (2 d-10 d after sowing). Finally, by comparing AChE up-regulated plants with wild-type, we found that AChE overexpression causes an enhanced gravitropic response. This result clearly suggests that the function of the rice AChE relate to positive regulation of gravitropic response in rice seedlings.

High-resolution mass spectrometry for detecting Acetylcholine in Arabidopsis

Acetylcholine (ACh) was first identified a century ago, and has long been known as a neurotransmitter in animals. However, it has been shown recently that the occurrence of ACh is widespread among various non-animal species including higher plants. Although previous reports suggest that various plant species are capable of responding to exogenously applied ACh, the molecular basis for ACh biosynthesis and regulatory mechanisms mediated by endogenous ACh are largely unclear. This is partly because of the lack of conclusive data on the occurrence and the tissue specificity of ACh in plants. To this end, we performed various analyses including liquid chromatography electro-chemical detection (LC-ECD), liquid chromatography tandem mass spectrometry (LC-MS/MS) analysis. The results, together with electrospray ionization-orbitrap Fourier transform mass spectrometry (ESI-orbitrap FT-MS) analysis provide strong evidence that ACh exists in Arabidopsis thaliana tissues. The results also showed that the level of ACh is highest in seed, followed by root and cotyledon. Moreover, exogenously applied ACh inhibited the elongation of Arabidopsis root hairs. These results collectively indicate that ACh exists primarily in seed and root in Arabidopsis seedlings, and plays a pivotal role during the initial stages of seedling development by controlling root hair elongation in Arabidopsis.

Microorganism and filamentous fungi drive evolution of plant synapses

In the course of plant evolution, there is an obvious trend toward an increased complexity of plant bodies, as well as an increased sophistication of plant behavior and communication. Phenotypic plasticity of plants is based on the polar auxin transport machinery that is directly linked with plant sensory systems impinging on plant behavior and adaptive responses. Similar to the emergence and evolution of eukaryotic cells, evolution of land plants was also shaped and driven by infective and symbiotic microorganisms. These microorganisms are the driving force behind the evolution of plant synapses and other neuronal aspects of higher plants; this is especially pronounced in the root apices. Plant synapses allow synaptic cell–cell communication and coordination in plants, as well as sensory-motor integration in root apices searching for water and mineral nutrition. These neuronal aspects of higher plants are closely linked with their unique ability to adapt to environmental changes.

Dynamic protoneural networks in plants: a new approach of spontaneous extracellular potential variations

Taking as a basis of discussion Kalanchoe's spontaneous and evoked extracellular activities recorded at the whole plant level, we put the challenging questions: do these low-voltage variations, together with endocellular events, reflect integrative properties and complex behavior in plants? Does it reflect common perceptive systems in animal and plant species? Is the ability of plants to treat short-term variations and information transfer without nervous system relevant? Is a protoneural construction of the world by lower organisms possible? More generally, the aim of this paper is to reevaluate the probably underestimated role of plant surface potentials in the plant relation life, carefully comparing the biogenesis of both animal and plant organisms in the era of plant neurobiology. Knowing that surface potentials participate at least to morphogenesis, cell to cell coupling, long distance transmission and transduction of stimuli, some hypothesis are given indicating that plants have to be studied as environmental biosensors and non linear dynamic systems able to detect transitional states between perception and response to stimuli. This study is conducted in the frame of the "plasticity paradigm," which gives a theoretical model of evolutionary processes and suggests some hypothesis about the nature of complexity, information and behavior.

The Arabidopsis thaliana ortholog of a purported maize cholinesterase gene encodes a GDSL-lipase

Acetylcholinesterase is an enzyme that is intimately associated with regulation of synaptic transmission in the cholinergic nervous system and in neuromuscular junctions of animals. However the presence of cholinesterase activity has been described also in non-metazoan organisms such as slime molds, fungi and plants. More recently, a gene purportedly encoding for acetylcholinesterase was cloned from maize. We have cloned the Arabidopsis thaliana homolog of the Zea mays gene, At3g26430, and studied its biochemical properties. Our results indicate that the protein encoded by the gene exhibited lipase activity with preference to long chain substrates but did not hydrolyze choline esters. The At3g26430 protein belongs to the SGNH clan of serine hydrolases, and more specifically to the GDS(L) lipase family.

Biochemical and molecular characterisation of acetylcholinesterase in four field populations of Bactrocera dorsalis (Hendel) (Diptera: Tephritidae)

BACKGROUND

The oriental fruit fly, Bactrocera dorsalis, is a major pest that infects fruits and agricultural products worldwide. The latest resistance monitoring of B. dorsalis from mainland China has identified high levels of resistance to insecticides. In this study, the biochemical and molecular characteristics of acetylcholinesterase (AChE) in four field populations of B. dorsalis are investigated.

RESULTS

Among the four populations, the DG population and its purified AChE were found to be the least susceptible to malathion and five inhibitors, whereas the KM population and its purified AChE were the most susceptible. The highest catalytic activity of purified AChE was found for the KM population, and the catalytic activity of the DG population was the lowest. Among developmental stages, the AChE purified from larvae was found to be the most insusceptible to inhibitors, but its catalytic activity was the highest. Sequence analysis of the cDNA encoding AChE showed that some residue differences existed. However, no significant differences in expression levels of the AChE gene among populations and developmental stages were detected.

CONCLUSION

The results suggest that the decrease in susceptibility of B. dorsalis was mainly caused by decrease in AChE activity, and they provide a broad view on the relation between AChE and resistance.

Profiling and functional classification of esterases in olive (Olea europaea) pollen during germination

BACKGROUND AND AIMS

A pollen grain contains a number of esterases, many of which are released upon contact with the stigma surface. However, the identity and function of most of these esterases remain unknown. In this work, esterases from olive pollen during its germination were identifided and functionally characterized.

METHODS

The esterolytic capacity of olive (Olea europaea) pollen was examined using in vitro and in-gel enzymatic assays with different enzyme substrates. The functional analysis of pollen esterases was achieved by inhibition assays by using specific inhibitors. The cellular localization of esterase activities was performed using histochemical methods.

KEY RESULTS

Olive pollen showed high levels of non-specific esterase activity, which remained steady after hydration and germination. Up to 20 esterolytic bands were identified on polyacrylamide gels. All the inhibitors decreased pollen germinability, but only diisopropyl fluorophosphate (DIFP) hampered pollen tube growth. Non-specific esterase activity is localized on the surface of oil bodies (OBs) and small vesicles, in the pollen intine and in the callose layer of the pollen tube wall. Acetylcholinesterase (AChE) activity was mostly observed in the apertures, exine and pollen coat, and attached to the pollen tube wall surface and to small cytoplasmic vesicles.

CONCLUSIONS

In this work, for the first time a systematic functional characterization of esterase enzymes in pollen from a plant species with wet stigma has been carried out. Olive pollen esterases belong to four different functional groups: carboxylesterases, acetylesterases, AChEs and lipases. The cellular localization of esterase activity indicates that the intine is a putative storage site for esterolytic enzymes in olive pollen. Based on inhibition assays and cellular localization of enzymatic activities, it can be concluded that these enzymes are likely to be involved in pollen germination, and pollen tube growth and penetration of the stigma.

Multifunctionality and diversity of GDSL esterase/lipase gene family in rice (Oryza sativa L. japonica) genome: new insights from bioinformatics analysis

BACKGROUND

GDSL esterases/lipases are a newly discovered subclass of lipolytic enzymes that are very important and attractive research subjects because of their multifunctional properties, such as broad substrate specificity and regiospecificity. Compared with the current knowledge regarding these enzymes in bacteria, our understanding of the plant GDSL enzymes is very limited, although the GDSL gene family in plant species include numerous members in many fully sequenced plant genomes. Only two genes from a large rice GDSL esterase/lipase gene family were previously characterised, and the majority of the members remain unknown. In the present study, we describe the rice OsGELP (Oryza sativa GDSL esterase/lipase protein) gene family at the genomic and proteomic levels, and use this knowledge to provide insights into the multifunctionality of the rice OsGELP enzymes.

RESULTS

In this study, an extensive bioinformatics analysis identified 114 genes in the rice OsGELP gene family. A complete overview of this family in rice is presented, including the chromosome locations, gene structures, phylogeny, and protein motifs. Among the OsGELPs and the plant GDSL esterase/lipase proteins of known functions, 41 motifs were found that represent the core secondary structure elements or appear specifically in different phylogenetic subclades. The specification and distribution of identified putative conserved clade-common and -specific peptide motifs, and their location on the predicted protein three dimensional structure may possibly signify their functional roles. Potentially important regions for substrate specificity are highlighted, in accordance with protein three-dimensional model and location of the phylogenetic specific conserved motifs. The differential expression of some representative genes were confirmed by quantitative real-time PCR. The phylogenetic analysis, together with protein motif architectures, and the expression profiling were analysed to predict the possible biological functions of the rice OsGELP genes.

CONCLUSIONS

Our current genomic analysis, for the first time, presents fundamental information on the organization of the rice OsGELP gene family. With combination of the genomic, phylogenetic, microarray expression, protein motif distribution, and protein structure analyses, we were able to create supported basis for the functional prediction of many members in the rice GDSL esterase/lipase family. The present study provides a platform for the selection of candidate genes for further detailed functional study.

Tomato GDSL1 is required for cutin deposition in the fruit cuticle

The plant cuticle consists of cutin, a polyester of glycerol, hydroxyl, and epoxy fatty acids, covered and filled by waxes. While the biosynthesis of cutin building blocks is well documented, the mechanisms underlining their extracellular deposition remain unknown. Among the proteins extracted from dewaxed tomato (Solanum lycopersicum) peels, we identified GDSL1, a member of the GDSL esterase/acylhydrolase family of plant proteins. GDSL1 is strongly expressed in the epidermis of growing fruit. In GDSL1-silenced tomato lines, we observed a significant reduction in fruit cuticle thickness and a decrease in cutin monomer content proportional to the level of GDSL1 silencing. A significant decrease of wax load was observed only for cuticles of the severely silenced transgenic line. Fourier transform infrared (FTIR) analysis of isolated cutins revealed a reduction in cutin density in silenced lines. Indeed, FTIR-attenuated total reflectance spectroscopy and atomic force microscopy imaging showed that drastic GDSL1 silencing leads to a reduction in ester bond cross-links and to the appearance of nanopores in tomato cutins. Furthermore, immunolabeling experiments attested that GDSL1 is essentially entrapped in the cuticle proper and cuticle layer. These results suggest that GDSL1 is specifically involved in the extracellular deposition of the cutin polyester in the tomato fruit cuticle.

Tissue localization of maize acetylcholinesterase associated with heat tolerance in plants

Our recent study reported that maize acetylcholinesterase (AChE) activity in the coleoptile node is enhanced through a post-translational modification response to heat stress and transgenic plants overexpressing maize AChE gene had an elevated heat tolerance, which strongly suggests that maize AChE plays a positive, important role in maize heat tolerance. Here we present (1) maize AChE activity in the mesocotyl also enhances during heat stress and (2) maize AChE mainly localizes in vascular bundles including endodermis and epidermis in coleoptile nodes and mesocotyls of maize seedlings.

A Pseudomonas aeruginosa PAO1 acetylcholinesterase is encoded by the PA4921 gene and belongs to the SGNH hydrolase family

Through the use of molecular and biochemical experiments and bioinformatic tools, this work demonstrates that the PA4921 gene of the Pseudomonas aeruginosa PAO1 genome is a gene responsible for cholinesterase (ChoE) activity. Similar to the acetylcholinesterase (AchE) of Zea mays, this ChoE belongs to the SGNH hydrolase family. In mature ChoE, i.e., without a signal peptide, (18)Ser, (78)Gly, (127)N, and (268)H are conserved aminoacyl residues. Acetylthiocholine (ATC) and propionylthiocholine (PTC) are substrates of this enzyme, but butyrylcholine is an inhibitor. The enzyme also catalyzes the hydrolysis of the artificial esters p-nitrophenyl propionate (pNPP) and p-nitrophenyl butyrate (pNPB) but with lower catalytic efficiency with respect to ATC or PTC. The second difference is that pNPP and pNPB did not produce inhibition at high substrate concentrations, as occurred with ATC and PTC. These differences plus preliminary biochemical and kinetic studies with alkylammonium compounds led us to propose that this enzyme is an acetylcholinesterase (AchE) or propionylcholinesterase. Studies performed with the purified recombinant enzyme indicated that the substrate saturation curves and the catalytic mechanism are similar to those properties described for mammalian AchEs. Therefore, the results of this work suggest that the P. aeruginosa ChoE is an AchE that may also be found in Pseudomonas fluorescens.

Maize acetylcholinesterase is a positive regulator of heat tolerance in plants

We previously reported that native tropical zone plants showed high acetylcholinesterase (AChE) activity during heat stress, and that AChE activity in endodermal cells of maize seedlings was increased by heat treatment. However, the physiological role of AChE in heat stressed plants is still unclear. Here we report (1) tissue-specific expression and subcellular localization of maize AChE, (2) elevation of AChE activity and possible post-translational modifications of this enzyme under heat stress, and (3) involvement of AChE in plant heat stress tolerance. Maize AChE was mainly expressed in coleoptile nodes and seeds. Maize AChE fused with green fluorescent protein (GFP) was localized in extracellular spaces of transgenic rice plants. Therefore, in maize coleoptile nodes and seeds AChE mainly functions in the cell wall matrix. After heat treatment, enhanced maize AChE activity was observed by in vitro activity measurement and by in situ cytochemical staining; transcript and protein levels, however, were not changed. Protein gel blot analysis revealed two AChE isoforms (upper and lower); the upper-form gradually disappeared after heat treatment. Thus, maize AChE activity might be enhanced through a post-translational modification response to heat stress. Finally, we found that overexpression of maize AChE in transgenic tobacco plants enhanced heat tolerance relative to that of non-transgenic plants, suggesting AChE plays a positive role in maize heat tolerance.

Immobilization of rat brain acetylcholinesterase on porous gold-nanoparticle-CaCO₃ hybrid material modified Au electrode for detection of organophosphorous insecticides

An acetylcholinesterase (AChE) purified from rat brain was immobilized onto gold nanoparticles (AuNPs) assembled on the surface of porous calcium carbonate (CaCO(3)) microsphere. The resulting AChE-AuNPs-CaCO(3) bioconjugate was mounted on the surface of Au electrode with the help of silica sol-gel matrix to prepare the working electrode. This electrode was connected to Ag/AgCl (3M/saturated KCl) as standard and Pt wire as an auxiliary electrode through a potentiostat to construct an organophosphorus (OP) biosensor. The biosensor was based on inhibition of AChE by OP compounds/insecticides. The biosensor showed optimum response at pH 7.0, 30°C, when polarized at +0.2V. Two OP compounds, malathion and chlorpyrifos could be detected in the range of 0.1-100 nM and 0.1-70 nM, respectively at 2.0-3.0% inhibition level of AChE. The sensor was reactivated by immersing it in 0.1 mM 2-pyridine aldoxime for 10 min. The detection limit of the sensor was 0.1 nM for both malathion and chlorpyrifos. The biosensor exhibited good reusability (50 times without considerable loss) and storage stability (50% within 60 days, when stored at 4°C).

Cholinesterases: Structure, Role, and Inhibition

Acetilkolinesteraza (AChE; E.C. 3.1.1.7) i butirilkolinesteraza (BChE; E.C. 3.1.1.8) enzimi su koji se zbog svoje uloge u organizmu intenzivno istražuju unutar područja biomedicine i toksikologije. Iako strukturno homologni, ovi enzimi razlikuju se prema katalitičkoj aktivnosti, odnosno specifičnosti prema supstratima koje mogu hidrolizirati te selektivnosti za vezanje mnogih liganada. U ovom radu dan je pregled dosadašnjih istraživanja kolinesteraza i njihovih interakcija s ligandima i inhibitorima te su izdvojene aminokiseline aktivnog mjesta koje sudjeluju u tim interakcijama.

Comparative studies of acetylcholinesterase purified from three field populations of Liposcelis entomophila (enderlein) (psocoptera: liposcelididae)

Acetylcholinesterace (AChE) is known to be the major target for organophophate and carbamate insecticides and biomolecular changes to AChE have been demonstrated to be an important mechanism for insecticide resistance in many insect species. In this study, AChE from three field populations of Liposcelis entomophila (Enderlein) (Psocoptera: Liposcelididae) was purified by affinity chromatography and subsequently characterized by its Michaelis-Menten kinetics to determine if detectable changes to AChE have occurred. Bioassays revealed that the potential resistance threat of psocids in Sichuan Province (GH) was greater than either Hubei Province (WH) or Chongqing Municipality (BB). Compared to the other two populations, the WH population possessed the highest specific activity of purified AChE. Kinetic analyses indicated that the purified AChE from GH population expressed a significantly lower affinity to the substrate and a higher catalytic activity toward acetylthiocholine iodide (ATChI) (i.e., higher K(m) and V(max) values) than BB and WH populations. In vitro studies of AChE suggest that five inhibitors (aldicarb, eserine, BW284C51, omethoate, and propoxur) all possess strong inhibitory effects with eserine having the strongest inhibitory effect against purified AChE. According to bimolecular rate constants (k(i)), the purified AChE from GH population was least sensitive to all inhibitors except for omethoate. The differences in AChE among the three populations may be partially attributed to the differences in pesticide application and control practices for psocids among the three locations.

Characterization, sub-cellular localization and expression profiling of the isoprenylcysteine methylesterase gene family in Arabidopsis thaliana

BACKGROUND

Isoprenylcysteine methylesterases (ICME) demethylate prenylated protein in eukaryotic cell. Until now, knowledge about their molecular information, localization and expression pattern is largely unavailable in plant species. One ICME in Arabidopsis, encoded by At5g15860, has been identified recently. Over-expression of At5g15860 caused an ABA hypersensitive phenotype in transgenic Arabidopsis plants, indicating that it functions as a positive regulator of ABA signaling. Moreover, ABA induced the expression of this gene in Arabidopsis seedlings. The current study extends these findings by examining the sub-cellular localization, expression profiling, and physiological functions of ICME and two other ICME-like proteins, ICME-LIKE1 and ICME-LIKE2, which were encoded by two related genes At1g26120 and At3g02410, respectively.

RESULTS

Bioinformatics investigations showed that the ICME and other two ICME-like homologs comprise a small subfamily of carboxylesterase (EC 3.1.1.1) in Arabidopsis. Sub-cellular localization of GFP tagged ICME and its homologs showed that the ICME and ICME-like proteins are intramembrane proteins predominantly localizing in the endoplasmic reticulum (ER) and Golgi apparatus. Semi-quantitative and real-time quantitative PCR revealed that the ICME and ICME-like genes are expressed in all examined tissues, including roots, rosette leaves, cauline leaves, stems, flowers, and siliques, with differential expression levels. Within the gene family, the base transcript abundance of ICME-LIKE2 gene is very low with higher expression in reproductive organs (flowers and siliques). Time-course analysis uncovered that both ICME and ICME-like genes are up-regulated by mannitol, NaCl and ABA treatment, with ICME showing the highest level of up-regulation by these treatments. Heat stress resulted in up-regulation of the ICME gene significantly but down-regulation of the ICME-LIKE1 and ICME-LIKE2 genes. Cold and dehydration stimuli led to no significant change of both ICME and ICME-like gene expression. Mutant icme-like2-1 showed increased sensitivity to ABA but slightly decreased sensitivity to salt and osmotic stresses during seed germination.

CONCLUSIONS

It is concluded that the ICME family is involved in stress and ABA signaling in Arabidopsis, probably through mediating the process of demethylating prenylated proteins. Identification of these prenylated proteins will help to better understand the significance of protein prenylation in Planta.

Evolution: like any other science it is predictable

Evolutionary biology rejoices in the diversity of life, but this comes at a cost: other than working in the common framework of neo-Darwinian evolution, specialists in, for example, diatoms and mammals have little to say to each other. Accordingly, their research tends to track the particularities and peculiarities of a given group and seldom enquires whether there are any wider or deeper sets of explanations. Here, I present evidence in support of the heterodox idea that evolution might look to a general theory that does more than serve as a tautology ('evolution explains evolution'). Specifically, I argue that far from its myriad of products being fortuitous and accidental, evolution is remarkably predictable. Thus, I urge a move away from the continuing obsession with Darwinian mechanisms, which are entirely uncontroversial. Rather, I emphasize why we should seek explanations for ubiquitous evolutionary convergence, as well as the emergence of complex integrated systems. At present, evolutionary theory seems to be akin to nineteenth-century physics, blissfully unaware of the imminent arrival of quantum mechanics and general relativity. Physics had its Newton, biology its Darwin: evolutionary biology now awaits its Einstein.

The combined effect of Cd2+ and ACh on action potentials of Nitellopsis obtusa cells

Interrelations between the action of acetylcholine (ACh) and cadmium ions (Cd2+) on bioelectrogenesis of Nitellopsis obtusa cells were investigated. We analyzed repetitively triggered action potentials (AP), their reproducibility, shape and dynamics of membrane potential after AP induction. ACh significantly increased membrane permeability only at high concentrations (1 mM and 5 mM). Repolarisation level of action potential after the first stimulus was much more positive in all cells treated with ACh as compared to the control. Differences of membrane potentials between points just before the first and the second stimuli were 23.4±.0 mV (control); 40.4±5.9 mV (1 mM ACh solution) and 57.7 ± 8.5 mV (5 mM ACh solution). Cd2+ at 20 μM concentration was examined as a possible inhibitor of acetylcholinesterase (AChE) in vivo. We found that cadmium strengthens depolarizing effect of acetylcholine after the first stimulus. The highest velocity of AP repolarization was reduced after ACh application and Cd2+strengthened this effect. There were no differences in dynamics of membrane potential after repetitively triggered action potentials in ACh or ACh and Cd2+ solutions. This shows that cadmium in small concentration acts as inhibitor of acetylcholinesterase.

Cloning and expression of carp acetylcholinesterase gene in Pichia pastoris and characterization of the recombinant enzyme

The gene encoding acetylcholinesterase (AChE) was cloned from common carp muscle tissue. The full-length cDNA was 2368 bp that contains a coding region of 1902 bp, corresponding to a protein of 634 amino acids. The deduced amino acid sequence showed a significant homology with those of ichthyic AChEs and several common features among them, including T peptide encoded by exon T in the C-terminus. Three yeast expression vectors were constructed and introduced into the yeast Pichia pastoris. The transformant harboring carp AChE gene lacking exon T most effectively produced AChE activity extracellularly. The replacement of the native signal sequence with the yeast alpha-factor prepro signal sequence rather decreased the production. A decrease in cultivation temperature from 30 to 15 degrees C increased the activity production 32.8-fold. The purified recombinant AChE lacking T peptide, eluted as a single peak with a molecular mass of about 230 kDa on the gel filtration chromatography, exhibited the specific activity of 4970 U/mg. On the SDS-PAGE, three proteins with molecular masses of 73, 54, and 22 kDa were observed. These proteins were N-glycosylated, and their N-terminal sequence showed that the latter two were produced from the former probably by proteolytic cleavage at the C-terminal region. Thus, the recombinant AChE is homotrimer of three identical subunits with 73 kDa. The optimal temperature and pH of the recombinant were comparable to those of the native enzyme purified previously, but the values of kinetic parameters and the sensitivities to substrate inhibition and inhibitors were considerably different between them.

Subcellular localization of overexpressed maize AChE gene in rice plant

The ACh-mediated system consisting of acetylcholine (ACh), acetylcholine receptor (AChR) and acetylcholinesterase (AChE) is fundamental for nervous system function in animals and insects. Although plants lack a nervous system, both ACh and ACh-hydrolyzing activity have been widely recognized in the plant kingdom. The function of the plant ACh-mediated system is still unclear, despite more than 30 years of research. To understand ACh-mediated systems in plants, we previously purified maize AChE and cloned the corresponding gene from maize seedlings (Plant Physiology). In a recent paper in Planta, we also purified and cloned AChE from the legume plant siratro (Macroptilium atropurpureum). In comparison with electric eel AChE, both plant AChEs showed enzymatic properties of both animal AChE and animal butyrylcholinesterase. On the other hand, based on Pfam protein family analysis, both plant AChEs contain a consensus sequence of the lipase GDSL family, while the animal AChEs possess a distinct alpha/beta-hydrolase fold superfamily sequence, but no lipase GDSL sequence. Thus, neither plant AChE belongs to the well-known AChE family, which is distributed throughout the animal kingdom. To address the possible physiological roles of plant AChEs, we herein report our data from the immunological analysis of the overexpressed maize AChE gene in plants.

Characterization of trimeric acetylcholinesterase from a legume plant, Macroptilium atropurpureum Urb

We recently identified plant acetylcholinesterases (E.C.3.1.1.7; AChEs) homologous to the AChE purified from a monocotyledon, maize, that are distinct from the animal AChE family. In this study, we purified, cloned and characterized an AChE from a dicotyledon, siratro. The full-length cDNA of siratro AChE is 1,441 nucleotides, encoding a 382-residue protein that includes a signal peptide. This AChE is a disulfide-linked 125-kDa homotrimer consisting of 41-42 kDa subunits, in contrast to the maize AChE, which exists as a mixture of disulfide and non-covalently linked 88-kDa homodimers. The plant AChEs apparently consist of various quaternary structures, depending on the plant species, similar to the animal AChEs. We compared the enzymatic properties of the dimeric maize and trimeric siratro AChEs. Similar to electric eel AChE, both plant AChEs hydrolyzed acetylthiocholine (or acetylcholine) and propionylthiocholine (or propionylcholine), but not butyrylthiocholine (or butyrylcholine), and their specificity constant was highest against acetylcholine. There was no significant difference between the enzymatic properties of trimeric and dimeric AChEs, although two plant AChEs had low substrate turnover numbers compared with electric eel AChE. The two plant AChE activities were not inhibited by excess substrate concentrations. Thus, similar to some plant AChEs, siratro and maize AChEs showed enzymatic properties of both animal AChE and animal BChE. On the other hand, both siratro and maize AChEs exhibited low sensitivity to the AChE-specific inhibitor neostigmine bromide, dissimilar to other plant AChEs. These differences in enzymatic properties of plant AChEs may reflect the phylogenetic evolution of AChEs.

Translational control of recombinant human acetylcholinesterase accumulation in plants

Background

Codon usage differences are known to regulate the levels of gene expression in a species-specific manner, with the primary factors often cited to be mRNA processing and accumulation. We have challenged this conclusion by expressing the human acetylcholinesterase coding sequence in transgenic plants in its native GC-rich sequence and compared to a matched sequence with (dicotyledonous) plant-optimized codon usage and a lower GC content.

Results

We demonstrate a 5 to 10 fold increase in accumulation levels of the "synaptic" splice variant of human acetylcholinesterase in Nicotiana benthamiana plants expressing the optimized gene as compared to the native human sequence. Both transient expression assays and stable transformants demonstrated conspicuously increased accumulation levels. Importantly, we find that the increase is not a result of increased levels of acetylcholinesterase mRNA, but rather its facilitated translation, possibly due to the reduced energy required to unfold the sequence-optimized mRNA.

Conclusion

Our findings demonstrate that codon usage differences may regulate gene expression at different levels and anticipate translational control of acetylcholinesterase gene expression in its native mammalian host as well.

Ubiquitous expression of acetylcholine and its biological functions in life forms without nervous systems

Using a radioimmunoassay (RIA) with high specificity and sensitivity (1 pg/tube) for acetylcholine (ACh), we have been able to measure the ACh content in samples from the bacteria, archaea and eucarya domains of the universal phylogenetic tree. We found detectable levels of ACh to be ubiquitous in bacteria (e.g., Bacillus subtilis), archaea (e.g., Thermococcus kodakaraensis KOD1), fungi (e.g., shiitake mushroom and yeast), plants (e.g., bamboo shoot and fern) and animals (e.g., bloodworm and lugworm). The levels varied considerably, however, with the highest ACh content detected in the top portion of bamboo shoot (2.9 micromol/g), which contained about 80 times that found in rat brain. In addition, using the method of Fonnum, various levels of ACh-synthesizing activity also were detected, a fraction of which was catalyzed by a choline acetyltransferase (ChAT)-like enzyme (sensitive to bromoACh, a selective ChAT inhibitor) in T. kodakaraensis KOD1 (15%), bamboo shoot (91%) and shiitake mushroom (51%), bloodworm (91%) and lugworm (81%). Taken together, these findings demonstrate the ubiquitous expression of ACh and ACh-synthesizing activity among life forms without nervous systems, and support the notion that ACh has been expressed and may be active as a local mediator and modulator of physiological functions since the early beginning of life.