Cloned and expressed fungal phyA gene in alfalfa produces a stable phytase

Safety assessment of phytase transgenic maize 11TPY001 by 90-day feeding study in rats

11TPY001 is a transgenic maize that expresses the Aspergillus niger phyA2 gene which could significantly improve phosphorus bioavailability in monogastric animals. The present study was conducted to investigate the potential health effects of phytase transgenic maize 11TPY001 through a 90-day subchronic rodent feeding study. Maize grains from 11TPY001 or its parental counterpart maize OSL963 were incorporated into rodent diets at 12.5%, 25% and 50% concentrations by mass and administered to Sprague-Dawley rats (n = 10/sex/group) for 90 days. An additional control group of rats (n = 10/sex/group) were fed with common maize Zhengdan958 diets at 50% by mass. All formulated diets were nutritionally balanced. Body weights, food intake, hematology, serum chemistry, absolute and relative organ weights were measured, and gross as well as microscopic pathology were examined. Compared with rats fed OSL963 maize and the common maize diet groups, no adverse diet-related differences were observed in rats fed 11TPY001 maize diets with respect to clinical signs of toxicity, body weight/gain, food consumption/efficiency, hematology, clinical chemistry, organ weights, and gross and microscopic pathology. Under the conditions of this study, the results indicated that 11TPY001 did not cause any treatment related adverse effects in rats compared with its non-transgenic parental maize OSL963.

Effects of a novel corn-expressed E. coli phytase on digestibility of calcium and phosphorous, growth performance, and bone ash in young growing pigs1

Two experiments were conducted to test the hypothesis that a corn-expressed phytase increases growth performance, bone measurements, and nutrient digestibility by young growing pigs, if added to diets that are deficient in Ca and P. In Exp. 1, 60 pigs (initial BW: 10.78 ± 0.67 kg) were randomly allotted to 6 dietary treatments that included a positive control diet (PC; 0.70% total Ca and 0.60% total P) and a negative control diet (NC; 0.50% total Ca and 0.42% total P). Four additional diets were formulated by supplementing the NC diet with 250, 500, 1,000, or 1,500 phytase units (FTU)/kg. Diets were fed for 28 d and the individual BW of pigs on days 1 and 28 were recorded. Fecal samples were collected from days 25 to 27 to calculate apparent total tract digestibility (ATTD) of Ca and P. On the last day of the experiment, all pigs were euthanized, and the left femur was removed and analyzed for ash, Ca, and P. Results indicated that growth performance, ATTD of Ca and P, and bone ash measurements were reduced (P < 0.05) in NC fed pigs compared with PC fed pigs. However, growth performance, ATTD of Ca and P, and bone ash measurements were improved (linear and quadratic, P < 0.05) by including increasing concentrations of phytase to the NC diet. In Exp. 2, experimental procedures were similar to those used in Exp. 1. Forty-eight pigs (initial BW: 11.15 ± 0.85 kg) were randomly allotted to 6 dietary treatments in a 28-d experiment. Treatments included a PC diet, an NC diet, and 4 diets in which 500 or 1,000 FTU/kg of either the corn-expressed phytase or a commercial microbial phytase were added to the NC diet. Pigs fed the NC diet had reduced (P < 0.01) final BW, ADG, G:F, and bone ash concentrations compared with pigs fed the PC diet. When 500 FTU/kg phytase was fed, no differences were observed in growth performance or bone ash measurements between phytase sources, and there were no differences in growth performance among pigs fed 1,000 FTU/kg of either phytase source or the PC diet. However, regardless of concentration or source of phytase, pigs fed the PC diet had greater (P < 0.001) amount of bone ash, bone Ca, and bone P compared with pigs fed phytase diets. In conclusion, the corn-expressed phytase is effective in improving growth performance, Ca and P digestibility, and bone measurements in pigs fed diets that are deficient in Ca and P.

Multifunctionalizing the marine diatom Phaeodactylum tricornutum for sustainable co-production of omega-3 long chain polyunsaturated fatty acids and recombinant phytase

There is an urgent requirement for sustainable sources of food and feed due to world population growth. Aquaculture relies heavily on the fish meal and fish oils derived from capture fisheries, challenging sustainability of the production system. Furthermore, substitution of fish oil with vegetable oil and fish meal with plant seed meals in aquaculture feeds reduces the levels of valuable omega-3 long chain polyunsaturated fatty acids such as eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids, and lowers the nutritional value due to the presence of phytate. Addition of exogenous phytase to fish feed is beneficial for enhancing animal health and reducing phosphorus pollution. We have engineered the marine diatom Phaeodactylum tricornutum, accumulating high levels of EPA and DHA together with recombinant proteins: the fungal Aspergillus niger PhyA or the bacterial Escherichia coli AppA phytases. The removal of the N-terminal signal peptide further increased phytase activity. Strains engineered with fcpA and CIP1 promoters showed the highest level of phytase activity. The best engineered strain achieved up to 40,000 phytase activity units (FTU) per gram of soluble protein, thus demonstrating the feasibility of development of multifunctionalized microalgae to simultaneously produce industrially useful proteins and fatty acids to meet the demand of intensive fish farming activity.

Genetic transformation of tropical maize (Zea mays L.) inbred line with a phytase gene from Aspergillus niger

A full-length cDNA of phyA gene of Aspergillus niger, encoding phytase enzyme, was cloned and expressed in E. coli BL21 cells and assayed for its activity. The phyA cDNA consisted of 1404 bp, which encoded 467 amino acid residues. The phytase activity of purified phytase was 826.33 U/mL. The phyA gene under the control of endosperm-specific promoters was transformed into an Indian maize inbred line, UMI29, using particle bombardment-mediated transformation method to generate transgenic maize plants over-expressing phytase in seeds. PCR and GUS analyses demonstrated the presence of transgenes in T₀ transgenic plants and their stable inheritance in the T₁ progenies. Three transgenic events expressing detectable level of A. niger phytase were characterized by western blot analysis. Phytase activity of 463.158 U/kg of seed was observed in one of the events, JB-UMI29-Z17/2. The phytase activity of transgenic maize seeds was 5.5- to 7-fold higher than the wild-type UMI29 seeds and, consequently, the seeds had 0.6- to 5-fold higher inorganic phosphorus content.

Heterologous Expression of Secreted Bacterial BPP and HAP Phytases in Plants Stimulates Arabidopsis thaliana Growth on Phytate

Phytases are specialized phosphatases capable of releasing inorganic phosphate from myo-inositol hexakisphosphate (phytate), which is highly abundant in many soils. As inorganic phosphorus reserves decrease over time in many agricultural soils, genetic manipulation of plants to enable secretion of potent phytases into the rhizosphere has been proposed as a promising approach to improve plant phosphorus nutrition. Several families of biotechnologically important phytases have been discovered and characterized, but little data are available on which phytase families can offer the most benefits toward improving plant phosphorus intake. We have developed transgenic Arabidopsis thaliana plants expressing bacterial phytases PaPhyC (HAP family of phytases) and 168phyA (BPP family) under the control of root-specific inducible promoter Pht1;2. The effects of each phytase expression on growth, morphology and inorganic phosphorus accumulation in plants grown on phytate hydroponically or in perlite as the only source of phosphorus were investigated. The most enzymatic activity for both phytases was detected in cell wall-bound fractions of roots, indicating that these enzymes were efficiently secreted. Expression of both bacterial phytases in roots improved plant growth on phytate and resulted in larger rosette leaf area and diameter, higher phosphorus content and increased shoot dry weight, implying that these plants were indeed capable of utilizing phytate as the source of phosphorus for growth and development. When grown on phytate the HAP-type phytase outperformed its BPP-type counterpart for plant biomass production, though this effect was only observed in hydroponic conditions and not in perlite. Furthermore, we found no evidence of adverse side effects of microbial phytase expression in A. thaliana on plant physiology and seed germination. Our data highlight important functional differences between these members of bacterial phytase families and indicate that future crop biotechnologies involving such enzymes will require a very careful evaluation of phytase source and activity. Overall, our data suggest feasibility of using bacterial phytases to improve plant growth in conditions of phosphorus deficiency and demonstrate that inducible expression of recombinant enzymes should be investigated further as a viable approach to plant biotechnology.

Genetically modified phytase crops role in sustainable plant and animal nutrition and ecological development: a review

Globally, plant-derivatives especially cereals and legumes are the major staple food sources for animals. The seeds of these crops comprise of phytic acid, the major repository form of the phosphorus, which is not digestible by simple-stomached animals. However, it is the most important factor responsible for impeding the absorption of minerals by plants that eventually results in less use of fertilizers that ultimately cause eutrophication in water bodies. Although abundant phosphorus (P) exists in the soils, plants cannot absorb most of the P due to its conversion to unavailable forms. Hence, additional P supplementation is indispensable to the soil to promote crop yields which not only leads to soil infertility but also rapid depletion of non-renewable P reservoirs. Phytase/phosphatase enzyme is essential to liberate P from soils by plants and from seeds by monogastric animals. Phytases are kind of phosphatases which can hydrolyse the indigestible phytate into inorganic Phosphate (Pi) and lower myo-inositol. There are several approaches to mitigate the problems associated with phytate indigestibility. One of the best possible solutions is engineering crops to produce heterologous phytase to improve P utilization by monogastric animals, plant nutrition and sustainable ecological developments. Previously published reviews were focused on either soil phytate or seed-phytate, related issues, but this review will address both the problems as well as phytate related ecological problems. This review summarizes the overall view of engineered phytase crops and their role in sustainable agriculture, animal nutrition and ecological development.

Barley HvPAPhy_a as transgene provides high and stable phytase activities in mature barley straw and in grains

The phytase purple acid phosphatase (HvPAPhy_a) expressed during barley seed development was evaluated as transgene for overexpression in barley. The phytase was expressed constitutively driven by the cauliflower mosaic virus 35S-promoter, and the phytase activity was measured in the mature grains, the green leaves and in the dry mature vegetative plant parts left after harvest of the grains. The T2 -generation of HvPAPhy_a transformed barley showed phytase activity increases up to 19-fold (29 000 phytase units (FTU) per kg in mature grains). Moreover, also in green leaves and mature dry straw, phytase activities were increased significantly by 110-fold (52 000 FTU/kg) and 57-fold (51 000 FTU/kg), respectively. The HvPAPhy_a-transformed barley plants with high phytase activities possess triple potential utilities for the improvement of phosphate bioavailability. First of all, the utilization of the mature grains as feed to increase the release of bio-available phosphate and minerals bound to the phytate of the grains; secondly, the utilization of the powdered straw either directly or phytase extracted hereof as a supplement to high phytate feed or food; and finally, the use of the stubble to be ploughed into the soil for mobilizing phytate-bound phosphate for plant growth.

Bacillus phytases: Current status and future prospects

Phytases catalyze the hydrolysis of phytic acid in a stepwise manner to lower inositol phosphates, myo-inositol (having important role in metabolism and signal transduction pathways), and inorganic phosphate. These enzymes have been widely used in animal feed in order to improve phosphorus nutrition and to decrease pollution in animal waste. Compared to previously described phytases, the phytase (PhyL) from Bacillus licheniformis ATCC 14580 has attractive biochemical properties which can increase the profitability of several biotechnological procedures (animal nutrition, humain health…etc). Due to its amino acid sequence with critical substitutions, the PhyL could be a model to enhance other phytases features, in terms of thermal stability and high activity. Otherwise, an engineered PhyL, with low pH optimum, will represent a challenge within the class of β- propeller phytases.

Expression of Aspergillus nidulans phy gene in Nicotiana benthamiana produces active phytase with broad specificities

A full-length phytase gene (phy) of Aspergillus nidulans was amplified from the cDNA library by polymerase chain reaction (PCR), and it was introduced into a bacterial expression vector, pET-28a. The recombinant protein (rPhy-E, 56 kDa) was overexpressed in the insoluble fraction of Escherichia coli culture, purified by Ni-NTA resin under denaturing conditions and injected into rats as an immunogen. To express A. nidulans phytase in a plant, the full-length of phy was cloned into a plant expression binary vector, pPZP212. The resultant construct was tested for its transient expression by Agrobacterium-infiltration into Nicotiana benthamiana leaves. Compared with a control, the agro-infiltrated leaf tissues showed the presence of phy mRNA and its high expression level in N. benthamiana. The recombinant phytase (rPhy-P, 62 kDa) was strongly reacted with the polyclonal antibody against the nonglycosylated rPhy-E. The rPhy-P showed glycosylation, two pH optima (pH 4.5 and pH 5.5), an optimum temperature at 45~55 °C, thermostability and broad substrate specificities. After deglycosylation by peptide-N-glycosidase F (PNGase-F), the rPhy-P significantly lost the phytase activity and retained 1/9 of the original activity after 10 min of incubation at 45 °C. Therefore, the deglycosylation caused a significant reduction in enzyme thermostability. In animal experiments, oral administration of the rPhy-P at 1500 U/kg body weight/day for seven days caused a significant reduction of phosphorus excretion by 16% in rat feces. Besides, the rPhy-P did not result in any toxicological changes and clinical signs.

Production of Lupin Acid Phosphatase in Transgenic Rice for Use as a Phytate-hydrolyzing Enzyme in Animal Feed

The acid phosphatase gene from lupin was expressed in transgenic rice plants under the control of the maize ubiquitin promoter or rice chlorophyll a/b binding protein (Cab) promoter. Transgenic rice leaves exhibited up to an 18-fold increase in phytate-hydrolyzing activity. Based on the phytate-hydrolyzing activity at pH 5.5, more than 85% this activity was retained after heat-treatment at 80 degrees C for 15 min, and the heterologous enzyme in leaf sections and leaf extracts was relatively stable during storage. A distinct increase in released phosphate was observed when the heterologous enzyme was mixed with the feed extract. These results suggest that the heterologous enzyme in rice plants may maintain its desired characteristics as a phytate-hydrolyzing enzyme when added to animal feed.

Microbial phytases in phosphorus acquisition and plant growth promotion

Phosphorus (P) is one of the major constituents in energy metabolism and biosynthesis of nucleic acids and cell membranes with an important role in regulation of a number of enzymes. Soil phosphorous is an important macronutrient for plant growth. Phosphorus deficiency in soil is a major problem for agricultural production. Total soil P occurs in either organic or in organic form. Phytic acid as phytate (salts of phytic acid) is the major form of organic phosphorus in soil and it is not readily available to plants as a source of phosphorus because it either forms a complex with cations or adsorbs to various soil components. Phosphate solubilizing microorganisms are ubiquitous in soils and could play an important role in supplying P to plants. Microorganisms utilizing phytate are found in cultivated soils as well as in wetland, grassland and forest soils. Various fungi and bacteria (including plant growth promoting rhizobacteria) hydrolyze this organic form of phosphorus secreting phosphatases such as phytases and acidic/alkaline phosphatases. A large number of transgenic plants have been developed which were able to utilize sodium phytate as sole source of phosphorus. However, the recombinant phytases were similar to their wild type counterparts in terms of their properties. Increased phytase/phosphatase activity in transgenic plants may be an effective approach to promote their phytate-phosphorus utilization. The extracellular phytase activity of transgenic plant roots is a significant factor in the utilization of phosphorus from phytate. Furthermore, this indicated that an opportunity exists for using gene technology to improve the ability of plants to utilize accumulated forms of soil organic phosphorus. This review is focused on the role of phytases and phytase producing microbes in promoting the growth of different plants.

Phytase transgenic maize does not affect the development and nutrition utilization of Ostrinia furnacalis and Helicoverpa armigera

Use of transgenic maize expressing phytase in seeds as feedstuff can greatly increase phosphate availability to livestock and poultry. Because phosphorus is an essential mineral for all living organisms, growing of phytase transgenic maize may affect the performance of the arthropod community in maize fields. We conducted a preliminary study to assess the potential effects of phytase transgenic maize (BVLA430101) on two herbivore species, Ostrinia furnacalis (Guenée) and Helicoverpa armigera (Hübner), both of which are directly exposed to high concentrations of phytase caused by ingestion of transgenic maize kernels. Our results showed that for both species, survival and duration of the first and second instars and fresh weight of the third instar were not affected when fed transgenic phytase maize kernels compared with those fed nontransformed near isoline kernels. Similarly, there was no statistical difference detected for the same life table parameters when the herbivores were fed artificial diet containing either transgenic phytase maize meal or nontransformed maize meal. In addition, the nutrition utilization of the two species was evaluated with the same diet treatments by comparing the following indices: relative food consumption rate (RCR), relative metabolic rate (RMR), efficiency of approximate digestibility (EAD), efficiency of conversation of ingested food (ECI), and efficiency of conversation of digested food (ECD). No statistical difference was detected for any index of either species between transgenic maize and nontransformed maize treatments. These results provide useful baseline information for further studies to assess the potential effects of phytase transgenic maize on other arthropods in maize fields.

Expression of Acidothermus cellulolyticus E1 endo-beta-1,4-glucanase catalytic domain in transplastomic tobacco

As part of an effort to develop transgenic plants as a system for the production of lignocellulose-degrading enzymes, we evaluated the production of the endo-beta-1,4-glucanase E1 catalytic domain (E1cd) of Acidothermus cellulolyticus in transplastomic tobacco. In an attempt to increase the translation efficiency of the E1cd cassette, various lengths of the N-terminus of the psbA gene product were fused to the E1cd protein. The psbA gene of the plastid genome encodes the D1 polypeptide of photosystem II and is known to encode an efficiently translated mRNA. Experiments in an Escherichia coli expression system indicated that the fusion of short (10-22 amino acid) segments of D1 to E1cd resulted in modest increases in E1cd abundance and were compatible with E1cd activity. Plastid expression cassettes encoding unmodified E1cd and a 10-amino-acid D1 fusion (10nE1cd) were used to generate transplastomic tobacco plants. Expression of the E1cd open reading frame in transplastomic tobacco resulted in very low levels of the enzyme. The transplastomic plants accumulated a high level of E1cd mRNA, however, indicating that post-transcriptional processes were probably limiting the production of recombinant protein. The accumulation of 10nE1cd in transplastomic tobacco was approximately 200-fold higher than that of unmodified E1cd, yielding 10nE1cd in excess of 12% of total soluble protein in the extracts of the lower leaves. Most importantly, the active recombinant enzyme was recovered very easily and efficiently from dried plant material and constituted as much as 0.3% of the dry weight of leaf tissue.

Improving phosphorus acquisition of white clover (Trifolium repens L.) by transgenic expression of plant-derived phytase and acid phosphatase genes

Phosphate is one of the least available macronutrients restricting crop production in many ecosystems. A phytase gene (MtPHY1) and a purple acid phosphatase gene (MtPAP1), both isolated from the model legume Medicago truncatula, were introduced into white clover (Trifolium repens L.) by Agrobacterium-mediated transformation. The transgenes were driven by the constitutive CaMV35S promoter or the root-specific MtPT1 promoter. Transcripts were detected in roots of the transgenic plants. Phytase or acid phosphatase (APase) activities in root apoplasts of the transgenic plants were increased up to three-fold compared to the wild type control. After the plants were grown 80 days in sand pots supplied with organic phosphorus (Po) as the sole P source, dry weights of shoot tissues of the best performing transgenic plants almost doubled that of the control and were comparable to the counterparts supplied with inorganic phosphorus (Pi). Relative biomass production of the transgenics under Po treatment was over 90% and 80% of that from the Pi treatment when the plants were grown in hydroponics (40 days) and sand pots (80 days), respectively. In contrast, biomass of the wild type controls under Po treatment was only about 50% of the Pi treatment in either hydroponic cultures or sand pots. In addition, shoot P concentrations of the transgenic plants were significantly increased compared to the control. Transgenic plants accumulated much higher amounts of total P (up to 2.6-fold after 80 days of growth) than the control in Po supplied sand pots. The results showed that transgenic expression of MtPHY1 or MtPAP1 in white clover plants increased their abilities of utilizing organic phosphorus in response to P deficiency.

Yeast Phytases: Present Scenario and Future Perspectives

Phytases hydrolyze phytates to liberate soluble and thus readily utilizable inorganic phosphate. Although phytases are produced by various groups of microbes, yeasts being simple eukaryotes and mostly non-pathogenic with proven probiotic benefits can serve as ideal candidates for phytase research. The full potential of yeast phytases has not, however, been exploited. This review focuses attention on the present status of knowledge on the production, characterization, molecular characteristics, and cloning and over-expression of yeast phytases. Several potential applications of the yeast phytases in feeds and foods, and in the synthesis of lower myo-inositol phosphates are also discussed.

High levels of stable phytase accumulate in the culture medium of transgenic Medicago truncatula cell suspension cultures

The use of plants for production of recombinant proteins is becoming widely accepted. More recently, plant cell cultures have been proposed as valuable systems for producing a wide range of biologically active proteins. Such systems provide certain advantages over whole plants, but yields are still considered a limitation. In this study we established a Medicago truncatula cell suspension line expressing phytase from Aspergillus niger. Phytase is an N-glycosylated enzyme that breaks down indigestible phytate, resulting in an increased availability of phosphorus and other minerals in monogastric animals and reduced levels of phosphorus output in their manure. Various production systems have previously been used to express heterologous phytase, including several plant species. In this work, remarkable amounts of enzymatically active recombinant phytase were produced and secreted into the culture medium. Recombinant phytase accumulated to at least 25 mg/L and remained stable along the growth curve, and an enriched fraction with high enzymatic activity was easily obtained. We therefore propose M. truncatula cell suspension cultures as a potential system for the production of recombinant proteins. Most importantly, we have shown that, contrary to general belief, it is possible to achieve high levels of a functional recombinant protein in plant cell culture systems.

The sweet potato sporamin promoter confers high-level phytase expression and improves organic phosphorus acquisition and tuber yield of transgenic potato

The sweet potato sporamin promoter was used to control the expression in transgenic potato of the E. coli appA gene, which encodes a bifunctional enzyme exhibiting both acid phosphatase and phytase activities. The sporamin promoter was highly active in leaves, stems and different size tubers of transgenic potato, with levels of phytase expression ranging from 3.8 to 7.4% of total soluble proteins. Phytase expression levels in transgenic potato tubers were stable over several cycles of propagation. Field tests showed that tuber size, number and yield increased in transgenic potato. Improved phosphorus (P) acquisition when phytate was provided as a sole P source and enhanced microtuber formation in cultured transgenic potato seedlings when phytate was provided as an additional P source were observed, which may account for the increase in leaf chloroplast accumulation (important for photosynthesis) and tuber yield of field-grown transgenic potato supplemented with organic fertilizers. Animal feeding tests indicated that the potato-produced phytase supplement was as effective as a commercially available microbial phytase in increasing the availability of phytate-P to weanling pigs. This study demonstrates that the sporamin promoter can effectively direct high-level recombinant protein expression in potato tubers. Moreover, overexpression of phytase in transgenic potato not only offers an ideal feed additive for improving phytate-P digestibility in monogastric animals but also improves tuber yield, enhances P acquisition from organic fertilizers, and has a potential for phytoremediation.

Phytate: impact on environment and human nutrition. A challenge for molecular breeding

Phytic acid (PA) is the primary storage compound of phosphorus in seeds accounting for up to 80% of the total seed phosphorus and contributing as much as 1.5% to the seed dry weight. The negatively charged phosphate in PA strongly binds to metallic cations of Ca, Fe, K, Mg, Mn and Zn making them insoluble and thus unavailable as nutritional factors. Phytate mainly accumulates in protein storage vacuoles as globoids, predominantly located in the aleurone layer (wheat, barley and rice) or in the embryo (maize). During germination, phytate is hydrolysed by endogenous phytase(s) and other phosphatases to release phosphate, inositol and micronutrients to support the emerging seedling. PA and its derivatives are also implicated in RNA export, DNA repair, signalling, endocytosis and cell vesicular trafficking. Our recent studies on purification of phytate globoids, their mineral composition and dephytinization by wheat phytase will be discussed. Biochemical data for purified and characterized phytases isolated from more than 23 plant species are presented, the dephosphorylation pathways of phytic acid by different classes of phytases are compared, and the application of phytase in food and feed is discussed.

Functional specialization of Medicago truncatula leaves and seeds does not affect the subcellular localization of a recombinant protein

A number of recent reports suggest that the functional specialization of plant cells in storage organs can influence subcellular protein sorting, so that the fate of a recombinant protein tends to differ between seeds and leaves. In order to test the general applicability of this hypothesis, we investigated the fate of a model recombinant glycoprotein in the leaves and seeds of a leguminous plant, Medicago truncatula. Detailed analysis of immature seeds by immunofluorescence and electron microscopy showed that recombinant phytase carrying a signal peptide for entry into the endoplasmic reticulum was efficiently secreted from storage cotyledon cells. A second version of the protein carrying a C-terminal KDEL tag for retention in the endoplasmic reticulum was predominantly retained in the ER of seed cotyledon cells, but some of the protein was secreted to the apoplast and some was deposited in storage vacuoles. Importantly, the fate of the recombinant protein in the leaves was nearly identical to that in the seeds from the same plant. This shows that in M. truncatula, the unanticipated partial vacuolar delivery and secretion is not a special feature of seed cotyledon tissue, but are conserved in different specialized tissues. Further investigation revealed that the unexpected fate of the tagged variant of phytase likely resulted from partial loss of the KDEL tag in both leaves and seeds. Our results indicate that the previously observed aberrant deposition of recombinant proteins into storage organelles of seed tissue is not a general reflection of functional specialization, but also depends on the species of plant under investigation. This discovery will have an impact on the production of recombinant pharmaceutical proteins in plants.

Transgenic maize plants expressing a fungal phytase gene

Maize seeds are the major ingredient of commercial pig and poultry feed. Phosphorus in maize seeds exists predominantly in the form of phytate. Phytate phosphorus is not available to monogastric animals and phosphate supplementation is required for optimal animal growth. Undigested phytate in animal manure is considered a major source of phosphorus pollution to the environment from agricultural production. Microbial phytase produced by fermentation as a feed additive is widely used to manage the nutritional and environmental problems caused by phytate, but the approach is associated with production costs for the enzyme and requirement of special cares in feed processing and diet formulation. An alternative approach would be to produce plant seeds that contain high phytase activities. We have over-expressed Aspergillus niger phyA2 gene in maize seeds using a construct driven by the maize embryo-specific globulin-1 promoter. Low-copy-number transgenic lines with simple integration patterns were identified. Western-blot analysis showed that the maize-expressed phytase protein was smaller than that expressed in yeast, apparently due to different glycosylation. Phytase activity in transgenic maize seeds reached approximately 2,200 units per kg seed, about a 50-fold increase compared to non-transgenic maize seeds. The phytase expression was stable across four generations. The transgenic seeds germinated normally. Our results show that the phytase expression lines can be used for development of new maize hybrids to improve phosphorus availability and reduce the impact of animal production on the environment.

Growth promoting effect of a transgenic Bacillus mucilaginosus on tobacco planting

In this study, we have investigated the plant growth promoting effect of Bacillus mucilaginosus strain D(4)B(1), a rhizosphere soil organism, and its transgenic strain NKTS-3 on tobacco planting. The transgenic strain contains a phytase expression cassette that can express high active phytase extracellularly and hydrolyze phytate in the soil to liberate inorganic phosphorus for the growth of tobacco plants. Greenhouse study and field experiments showed that both wild-type B. mucilaginosus and the transgenic strain could promote tobacco plant growth. Moreover, the transgenic strain promoted tobacco plant growth (235% more than control in pot experiments and 125% more than control in field experiments) was higher than the wild-type B. mucilaginosus (183% more than control in pot experiments and 108% more than control in field experiments). In addition, the inoculation with transgenic rhizobacteria could significantly improve root acquisition of phosphorus and increase the phosphorus content of the plant.

Shifting the pH profile of Aspergillus niger PhyA phytase to match the stomach pH enhances its effectiveness as an animal feed additive

Environmental pollution by phosphorus from animal waste is a major problem in agriculture because simple-stomached animals, such as swine, poultry, and fish, cannot digest phosphorus (as phytate) present in plant feeds. To alleviate this problem, a phytase from Aspergillus niger PhyA is widely used as a feed additive to hydrolyze phytate-phosphorus. However, it has the lowest relative activity at the pH of the stomach (3.5), where the hydrolysis occurs. Our objective was to shift the pH optima of PhyA to match the stomach condition by substituting amino acids in the substrate-binding site with different charges and polarities. Based on the crystal structure of PhyA, we prepared 21 single or multiple mutants at Q50, K91, K94, E228, D262, K300, and K301 and expressed them in Pichia pastoris yeast. The wild-type (WT) PhyA showed the unique bihump, two-pH-optima profile, whereas 17 mutants lost one pH optimum or shifted the pH optimum from pH 5.5 to the more acidic side. The mutant E228K exhibited the best overall changes, with a shift of pH optimum to 3.8 and 266% greater (P < 0.05) hydrolysis of soy phytate at pH 3.5 than the WT enzyme. The improved efficacy of the enzyme was confirmed in an animal feed trial and was characterized by biochemical analysis of the purified mutant enzymes. In conclusion, it is feasible to improve the function of PhyA phytase under stomach pH conditions by rational protein engineering.

The intracellular fate of a recombinant protein is tissue dependent

Recombinant proteins directed to the secretory pathway in plants require a signal peptide for entry into the endoplasmic reticulum. In the absence of further targeting information, such proteins are generally secreted via the default pathway to the apoplast. This has been well documented in protoplasts and leaf tissue, but the trafficking of recombinant proteins in seeds and other storage tissues has rarely been investigated. We used Aspergillus niger phytase as a model glycoprotein to compare the intracellular fate of a recombinant protein in the leaves and seeds of rice (Oryza sativa). Using fluorescence and electron microscopy we showed that the recombinant protein was efficiently secreted from leaf cells as expected. In contrast, within endosperm cells it was retained in endoplasmic reticulum-derived prolamin bodies and protein storage vacuoles. Consistent with our immunolocalization data, the phytase produced in endosperm cells possessed oligomannose and vacuolar-type N-glycans [Man(3)(Xyl)(Fuc)GlcNAc(2)], whereas the phytase produced in leaves contained predominantly secretion-type N-glycans [GlcNAc(2)Man(3)(Xyl)(Fuc)GlcNAc(2)]. The latter could not be detected in preparations of the endosperm-derived phytase. Our results show that the intracellular deposition and modification of a recombinant protein is tissue dependent.

Properties of beta-propeller phytase expressed in transgenic tobacco

Phytases are enzymes that liberate inorganic phosphates from phytate. In a previous study, a beta-propeller phytase (168phyA) from Bacillus subtilis was introduced into transgenic tobacco, which resulted in certain phenotypic changes. In the study described herein, the recombinant phytase (t168phyA) was purified from transgenic tobacco to near homogeneity by a three-step purification scheme. The biochemical properties and kinetic parameters of t168phyA were compared with those of its counterpart from B. subtilis. t168phyA was glycosylated, and it showed a 4 kDa increase in molecular size in SDS-PAGE (44 kDa vs. 40 kDa). Although its thermostability remained unchanged, its temperature optimum shifted from 60 degrees C to 45-50 degrees C and its pH optimum shifted from pH 5.5 to 6.0. Kinetic data showed that the t168phyA had a lower Kcat, but a higher Km than the native enzyme. Despite these changes, t168phyA remained catalytically active and has a specific activity of 2.3 U/mg protein. These results verify the activity of recombinant Bacillus phytase that is expressed in plants.

Codon-modifications and an endoplasmic reticulum-targeting sequence additively enhance expression of an Aspergillus phytase gene in transgenic canola

Transgenic plants offer advantages for biomolecule production because plants can be grown on a large scale and the recombinant macromolecules can be easily harvested and extracted. We introduced an Aspergillus phytase gene into canola (Brassica napus) (line 9412 with low erucic acid and low glucosinolates) by Agrobacterium-mediated transformation. Phytase expression in transgenic plant was enhanced with a synthetic phytase gene according to the Brassica codon usage and an endoplasmic reticulum (ER) retention signal KDEL that confers an ER accumulation of the recombinant phytase. Secretion of the phytase to the extracellular fluid was also established by the use of the tobacco PR-S signal peptide. Phytase accumulation in mature seed accounted for 2.6% of the total soluble proteins. The enzyme can be glycosylated in the seeds of transgenic plants and retain a high stability during storage. These results suggest a commercial feasibility of producing a stable recombinant phytase in canola at a high level for animal feed supplement and for reducing phosphorus eutrophication problems.

Endosperm-specific co-expression of recombinant soybean ferritin and Aspergillus phytase in maize results in significant increases in the levels of bioavailable iron

We have generated transgenic maize plants expressing Aspergillus phytase either alone or in combination with the iron-binding protein ferritin. Our aim was to produce grains with increased amounts of bioavailable iron in the endosperm. Maize seeds expressing recombinant phytase showed enzymatic activities of up to 3 IU per gram of seed. In flour paste prepared from these seeds, up to 95% of the endogenous phytic acid was degraded, with a concomitant increase in the amount of available phosphate. In seeds expressing ferritin in addition to phytase, the total iron content was significantly increased. To evaluate the impact of the recombinant proteins on iron absorption in the human gut, we used an in vitro digestion/Caco-2 cell model. We found that phytase in the maize seeds was associated with increased cellular iron uptake, and that the rate of iron uptake correlated with the level of phytase expression regardless of the total iron content of the seeds. We also investigated iron bioavailability under more complex meal conditions by adding ascorbic acid, which promotes iron uptake, to all samples. This resulted in a further increase in iron absorption, but the effects of phytase and ascorbic acid were not additive. We conclude that the expression of recombinant ferritin and phytase could help to increase iron availability and enhance the absorption of iron, particularly in cereal-based diets that lack other nutritional components.

Biotechnological production and applications of phytases

Phytases decompose phytate, which is the primary storage form of phosphate in plants. More than 10 years ago, the first commercial phytase product became available on the market. It offered to help farmers reduce phosphorus excretion of monogastric animals by replacing inorganic phosphates by microbial phytase in the animal diet. Phytase application can reduce phosphorus excretion by up to 50%, a feat that would contribute significantly toward environmental protection. Furthermore, phytase supplementation leads to improved availability of minerals and trace elements. In addition to its major application in animal nutrition, phytase is also used for processing of human food. Research in this field focuses on better mineral absorption and technical improvement of food processing. All commercial phytase preparations contain microbial enzymes produced by fermentation. A wide variety of phytases were discovered and characterized in the last 10 years. Initial steps to produce phytase in transgenic plants were also undertaken. A crucial role for its commercial success relates to the formulation of the enzyme solution delivered from fermentation. For liquid enzyme products, a long shelf life is achieved by the addition of stabilizing agents. More comfortable for many customers is the use of dry enzyme preparations. Different formulation technologies are used to produce enzyme powders that retain enzyme activity, are stable in application, resistant against high temperatures, dust-free, and easy to handle.

Construction of transgenic Bacillus mucilaginosus strain with improved phytase secretion

AIMS

To construct a transgenic Bacillus mucilaginosus strain to increase the secretion capability of a wild-type isolate of B. mucilaginosus D4B1 to hydrolyse phytate phosphorus, which can be used as a microbial fertilizer in field application.

METHODS AND RESULTS

We constructed a phytase secreting expression vector pSP43 with a mini-Tn5 transposon and a Aspergillus fumigatus phytase expression cassette. The vector pSP43 was successfully transferred into the wild-type B. mucilaginosus using the particle bombardment method, and three transgenic strains with a stable copy of phytase expression cassette integrated into the chromosome of the B. mucilaginosus by Tn5 transposition were selected. The phytase activity of the engineered strains increased 36-46-fold when compared with the wild-type strain of D4B1.

CONCLUSIONS

The A. fumigatus phytase gene can be expressed under the direction of p43 promoter in B. mucilaginosus. The expression protein is secreted extracellularly and newly constructed strains showed a high phytase activity.

SIGNIFICANCE AND IMPACT OF THE STUDY

A transgenic Bacillus strain by the particle bombardment method was constructed.

Plants as bioreactors: a comparative study suggests that Medicago truncatula is a promising production system

Plants are emerging as a promising alternative to conventional platforms for the large-scale production of recombinant proteins. This field of research, known as molecular farming, is developing rapidly and several plant-derived recombinant proteins are already in advanced clinical trials. However, the full potential of molecular farming can only be realized if we gain a fundamental understanding of biological processes regulating the production and accumulation of functional recombinant proteins in plants. Recent studies indicate that species- and tissue-specific factors as well as plant physiology can have a significant impact on the amount and quality of the recombinant product. More detailed comparative studies are needed for each product, including the analysis of expression levels, biochemical properties, in vitro activity and subcellular localization. In this review we include the first results from an extensive comparative study in which the highly glycosylated enzyme phytase (from the fungus Aspergillus niger) was produced in different plant species (including tobacco and the model legume Medicago truncatula). Special emphasis is placed on M. truncatula, whose leaves accumulated the highest levels of active phytase. We discuss the potential of this species as a novel production host.

High-level production of yeast (Schwanniomyces occidentalis) phytase in transgenic rice plants by a combination of signal sequence and codon modification of the phytase gene

This study was designed to produce yeast (Schwanniomyces occidentalis) phytase in rice with a view to future applications in the animal feed industry. To achieve high-level production, chimeric genes with the secretory signal sequence of the rice chitinase-3 gene were constructed using either the original full-length or N-truncated yeast phytase gene, or a modified gene whose codon usage was changed to be more similar to that of rice, and then introduced into rice (Oryza sativa L.). When the original phytase genes were used, the phytase activity in the leaves of transgenic rice was of the same level as in wild-type plants, whose mean value was 0.039 U/g fresh weight (g-FW) (1 U of activity was defined as 1 micromol P released per min at 37 degrees C). In contrast, the enzyme activity was increased markedly when codon-modified phytase genes were introduced: up to 4.6 U/g-FW of leaves for full-length codon-modified phytase, and 10.6 U/g-FW for truncated codon-modified phytase. A decrease in the optimum temperature and thermal stability was observed in the truncated heterologous enzyme, suggesting that the N-terminal region plays an important role in enzymatic properties. In contrast, the optimum temperature and pH of full-length heterologous phytase were indistinguishable from those of the benchmark yeast phytase, although the heterologous enzyme was less glycosylated. Full-length heterologous phytase in leaf extract showed extreme stability. These results indicate that codon modification, combined with the use of a secretory signal sequence, can be used to produce substantial amounts of yeast phytase, and possibly any phytases from various organisms, in an active and stable form.

Modification of plant N-glycans processing: The future of producing therapeutic protein by transgenic plants

Transgenic plants are regarded as one of the most promising systems for the production of human therapeutic proteins. The number of therapeutic proteins successfully produced in plants is steadily arising. However, the glycoproteins normally produced from plants are not the same as native therapeutic proteins produced from mammals or humans. In addition to in vitro enzymatic modeling glycoproteins, there are two gene manipulation strategies to humanize plant N-glycans connected to the glycoproteins. One is retaining the recombinant glycoproteins in endoplasmic reticulum (ER), the site where few specific modifications of N-glycans occurs. The other is inhibiting the plant endogenous Golgi glycosyltransferase and/or adding new glycosyltransferase from mammalians. In this review, the biosynthesis of N-glycans in plants, the modification of the plant N-glycans processing will be discussed.

Production of two highly active bacterial phytases with broad pH optima in germinated transgenic rice seeds

Phytate is the main storage form of phosphorus in many plant seeds, but phosphate bound in this form is not available to monogastric animals. Phytase, an enzyme that hydrolyzes phosphate from phytate, has the potential to enhance phosphorus availability in animal diets when engineered in rice seeds as a feed additive. Two genes, derived from a ruminal bacterium Selenomonas ruminantium (SrPf6) and Escherichia coli (appA), encoding highly active phytases were expressed in germinated transgenic rice seeds. Phytase expression was controlled by a germination inducible alpha-amylase gene (alphaAmy8) promoter, and extracellular phytase secretion directed by an betaAmy8 signal peptide sequence. The two phytases were expressed in germinated transgenic rice seeds transiently and in a temporally controlled and tissue-specific manner. No adverse effect on plant development or seed formation was observed. Up to 0.6 and 1.4 U of phytase activity per mg of total extracted cellular proteins were obtained in germinated transgenic rice seeds expressing appA and SrPf6 phytases, respectively, which represent 46-60 times of phytase activities compared to the non-transformant. The appA and SrPf6 phytases produced in germinated transgenic rice seeds had high activity over broad pH ranges of 3.0-5.5 and 2.0-6.0, respectively. Phytase levels and inheritance of transgenes in one highly expressing plant were stable over four generations. Germinated transgenic rice seeds, which produce a highly active recombinant phytase and are rich in hydrolytic enzymes, nutrients and minerals, could potentially be an ideal feed additive for improving the phytate-phosphorus digestibility in monogastric animals.

Phytases: microbial sources, production, purification, and potential biotechnological applications

The review deals with phytase-producing microorganisms along with optimum conditions for its production. Various methods used for purifying phytases and their characteristics are discussed. Heterologous gene expression, cost-effective large-scale phytase production, and various biotechnological applications of the enzyme in animal feed and food industries are also discussed.

Directed evolution of industrial enzymes: an update

The use of enzymes in industrial processes can often eliminate the use of high temperatures, organic solvents and extremes of pH, while at the same time offering increased reaction specificity, product purity and reduced environmental impact. The growing use of industrial enzymes is dependent on constant innovation to improve performance and reduce cost. This innovation is driven by a rapidly increasing database of natural enzyme diversity, recombinant DNA and fermentation technologies that allow this diversity to be produced at low cost, and protein modification tools that enable enzymes to be tuned to fit into the industrial marketplace.

Fungal phyA gene expressed in potato leaves produces active and stable phytase

Fungal phyA gene from Aspergillus ficuum (niger) was cloned and expressed in potato leaves. The recombinant enzyme was stable and catalytically active. The expressed protein in the leaves of the dicotyledonous plant retained most physical and catalytic properties of the benchmark A. ficuum phytase. The expressed enzyme was, however, 15% less glycosylated than the native phytase. The usual bi-hump pH optima profile, which is characteristic of the fungal phytase, was altered; however, the pH optimum at 5.0 was unchanged for phytate and at 4.0 for synthetic substrate p-nitrophenyl phosphate. The temperature was, however, unchanged. The expressed phytase was found to be as sensitive as the native enzyme to the inhibitory action of pseudo substrate, myo-inositol hexasulfate, while losing about 90% of the activity at 20 microM inhibitor concentration. Similar to the benchmark phytase, the expressed phytase in leaves was completely inactivated by Arg modifier phenylglyoxal at 60 nM. In addition, the expressed phytase in the leaves was inhibited by antibody raised against a 20-mer internal peptide, which is present on the surface of the molecule as shown by the X-ray deduced 3D structure of fungal phytase. Taken together, the biochemical evidences indicate that fungal phytase when cloned and expressed in potato leaves produces a stable and active biocatalyst. 'Biofarming,' therefore, is an alternative way to produce functional hydrolytic enzymes as exemplified by the expression of A. ficuum (niger) phyA gene in potato leaf.