Recombinant protein expression in proteome-reduced cells under aerobic and oxygen-limited regimes

Industrial cultures are hindered by the physiological complexity of the host and the limited mass transfer capacity of conventional bioreactors. In this study, a minimal cell approach was combined with genetic devices to overcome such issues. A flavin mononucleotide-based fluorescent protein (FbFP) was expressed in a proteome-reduced Escherichia coli (PR). When FbFP was expressed from a constitutive protein generator (CPG), the PR strain produced 47% and 35% more FbFP than its wild type (WT), in aerobic or oxygen-limited regimes, respectively. Metabolic and expression models predicted more efficient biomass formation at higher fluxes to FbFP, in agreement with these results. A microaerobic protein generator (MPG) and a microaerobic transcriptional cascade (MTC) were designed to induce FbFP expression upon oxygen depletion. The FbFP fluorescence using the MTC in the PR strain was 9% higher than that of the WT bearing the CPG under oxygen limitation. To further improve the PR strain, the pyruvate dehydrogenase complex regulator gene was deleted, and the Vitreoscilla hemoglobin was expressed. Compared to oxygen-limited cultures of the WT, the engineered strains increased the FbFP expression more than 50% using the MTC. Therefore, the designed expression systems can be a valuable alternative for industrial cultivations.

Transport-controlled growth decoupling for self-induced protein expression with a glycerol-repressible genetic circuit

Decoupling cell formation from recombinant protein synthesis is a potent strategy to intensify bioprocesses. Escherichia coli strains with mutations in the glucose uptake components lack catabolite repression, display low growth rate, no overflow metabolism, and high recombinant protein yields. Fast growth rates were promoted by the simultaneous consumption of glucose and glycerol, and this was followed by a phase of slow growth, when only glucose remained in the medium. A glycerol-repressible genetic circuit was designed to autonomously induce recombinant protein expression. The engineered strain bearing the genetic circuit was cultured in 3.9 g L-1 glycerol + 18 g L-1 glucose in microbioreactors with online oxygen transfer rate monitoring. The growth was fast during the simultaneous consumption of both carbon sources (C-sources), while expression of the recombinant protein was low. When glycerol was depleted, the growth rate decreased, and the specific fluorescence reached values 17% higher than those obtained with a strong constitutive promoter. Despite the relatively high amount of C-source used, no oxygen limitation was observed. The proposed approach eliminates the need for the substrate feeding or inducers addition and is set as a simple batch culture while mimicking fed-batch performance.

Effect of Basic Amino Acids on Folic Acid Solubility

To prevent neural tube defects and other cardiovascular diseases in newborns, folic acid (FA) is recommended in pregnant women. A daily dose of 600 µg FA consumption is widely prescribed for women during pregnancy and 400 µg for women with childbearing potential. FA is a class IV compound according to the Biopharmaceutics Classification System (BCS) due to its low permeability (1.7 × 10-6 cm/s) and low solubility (1.6 mg/L); therefore, it must be administered via a formulation that enhances its solubility. Studies reported in the literature have proved that co-amorphization and salt formation of a poorly soluble drug with amino acids (AA) can significantly increase its solubility. Although arginine has been used with FA as a supplement, there is no information on the effect of basic AA (arginine and lysine) on the physical and chemical properties of FA-AA binary formulations. The present study implemented a conductimetric titration methodology to find the effective molar ratio to maximize FA solubility. The results showed that a 1:2.5 FA:AA molar ratio maximized solubility for arginine and lysine. Binary formulations were prepared using different methods, which led to an amorphous system confirmed by the presence of a glass transition, broad FTIR bands, and the absence of an X-ray diffraction pattern. Results of FA:AA (1:2.5) solubility increased in the range of 5500-6000 times compared with pure FA. In addition to solubility enhancement, the binary systems presented morphological properties that depend on the preparation method and whose consideration could be strategic for scaling purposes.

Glucose transport engineering allows mimicking fed-batch performance in batch mode and selection of superior producer strains

Background

Fed-batch mode is the standard culture technology for industrial bioprocesses. Nevertheless, most of the early-stage cell and process development is carried out in batch cultures, which can bias the initial selection of expression systems. Cell engineering can provide an alternative to fed-batch cultures for high-throughput screening and host selection. We have previously reported a library of Escherichia coli strains with single and multiple deletions of genes involved in glucose transport. Compared to their wild type (W3110), the mutant strains displayed lower glucose uptake, growth and aerobic acetate production rates. Therefore, when cultured in batch mode, such mutants may perform similar to W3110 cultured in fed-batch mode. To test that hypothesis, we evaluated the constitutive expression of the green fluorescence protein (GFP) in batch cultures in microbioreactors using a semi defined medium supplemented with 10 or 20 g/L glucose + 0.4 g yeast extract/g glucose.

Results

The mutant strains cultured in batch mode displayed a fast-growth phase (growth rate between 0.40 and 0.60 h⁻¹) followed by a slow-growth phase (growth rate between 0.05 and 0.15 h⁻¹), similar to typical fed-batch cultures. The phase of slow growth is most probably caused by depletion of key amino acids. Three mutants attained the highest GFP fluorescence. Particularly, a mutant named WHIC (ΔptsHIcrr, ΔmglABC), reached a GFP fluorescence up to 14-fold greater than that of W3110. Strain WHIC was cultured in 2 L bioreactors in batch mode with 100 g/L glucose + 50 g/L yeast extract. These cultures were compared with exponentially fed-batch cultures of W3110 maintaining the same slow-growth of WHIC (0.05 h⁻¹) and using the same total amount of glucose and yeast extract than in WHIC cultures. The WHIC strain produced approx. 450 mg/L GFP, while W3110 only 220 mg/L.

Conclusion

The combination of cell engineering and high throughput screening allowed the selection of a particular mutant that mimics fed-batch behavior in batch cultures. Moreover, the amount of GFP produced by the strain WHIC was substantially higher than that of W3110 under both, batch and fed-batch schemes. Therefore, our results represent a valuable technology for accelerated bioprocess development.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-022-01906-1.

Global transcriptomic response of Escherichia coli to p-coumaric acid

The aromatic compound p-coumaric acid (p-CA) is a secondary metabolite produced by plants. This aromatic acid and derived compounds have positive effects on human health, so there is interest in producing them in biotechnological processes with recombinant Escherichia coli strains. To determine the physiologic response of E. coli W3110 to p-CA, dynamic expression analysis of selected genes fused to a fluorescent protein reporter as well as RNA-seq and RT-qPCR were performed. The observed transcriptional profile revealed the induction of genes involved in functions related to p-CA active export, synthesis of cell wall and membrane components, synthesis of amino acids, detoxification of formaldehyde, phosphate limitation, acid stress, protein folding and degradation. Downregulation of genes encoding proteins involved in energy production, carbohydrate import and metabolism, as well as several outer and plasma membrane proteins was detected. This response is indicative of cell envelope damage causing the leakage of intracellular components including amino acids and phosphate-containing compounds. The cellular functions responding to p-CA that were identified in this study will help in defining targets for production strains improvement.

Induced Changes in Aroma Compounds of Foods Treated with High Hydrostatic Pressure: A Review

Since conventional thermal processing can have detrimental consequences on aroma compounds, non-thermal technologies such as high hydrostatic pressure (HHP) have been explored. HHP may alter the weak chemical bonds of enzymes. These changes can modify the secondary, tertiary, and quaternary structures of key enzymes in the production of aroma compounds. This can result in either an increase or decrease in their content, along with reactions or physical processes associated with a reduction of molecular volume. This article provides a comprehensive review of HHP treatment's effects on the content of lipid-derived aroma compounds, aldehydes, alcohols, ketones, esters, lactones, terpenes, and phenols, on various food matrices of vegetable and animal origin. The content of aldehydes and ketones in food samples increased when subjected to HHP, while the content of alcohols and phenols decreased, probably due to oxidative processes. Both ester and lactone concentrations appeared to decline due to hydrolysis reactions. There is no clear tendency regarding terpenes concentration when subjected to HHP treatments. Because of the various effects of HHP on aroma compounds, an area of opportunity arises to carry out future studies that allow optimizing and controlling the effect.

Methods for the Modification and Evaluation of Cereal Proteins for the Substitution of Wheat Gluten in Dough Systems

The substitution of wheat gluten in the food industry is a relevant research area because the only known treatment for celiac disease is abstinence from this protein complex. The use of gluten-free cereals in dough systems has demonstrated that the viscoelastic properties of gluten cannot be achieved without the modification of the protein fraction. The quality of the final product is determined by the ability of the modification to form a matrix similar to that of gluten and to reach this, different methods have been proposed and tested. These procedures can be classified into four main types: chemical, enzymatic, physical, and genetic. This article provides a comprehensive review of the most recent research done in protein modification of cereal and pseudocereals for gluten substitution. The reported effects and methodologies for studying the changes made with each type of modification are described; also, some opportunity areas for future works regarding the study of the effect of protein modifications on gluten-free products are presented.

Buccal dental-microwear and feeding ecology of Early Pleistocene Theropithecus oswaldi from Cueva Victoria (Spain)

Despite the scarcity of fossil specimens of Theropithecus oswaldi in Eurasia, its presence out of Africa attests to the great dispersal of this Papionini genus during the Early Pleistocene. In the present study, we analyze the buccal dental microwear of T. oswaldi (T. o. leakeyi) fossil specimens from Cueva Victoria (Southeastern Spain). This analysis is the first characterization of the feeding ecology of T. oswaldi in Europe. The buccal microwear pattern of the molar and premolar teeth of T. oswaldi from Cueva Victoria shows great similarities to that observed for the extant frugivorous forest-dwelling Mandrillus sphinx and mangabeys (Cercocebus sp.)-both species adapted to durophagous dietary habits-while significantly different from that observed for the gramnivorous Theropithecus gelada. These results suggest that T. oswaldi from Cueva Victoria could have exploited both hard-shelled fruits or seeds and succulent fruits from open and forested Mediterranean ecosystems.

Production of Melanins With Recombinant Microorganisms

The melanins constitute a diverse group of natural products found in most organisms, having functions related to protection against chemical and physical stresses. These products originate from the enzyme-catalyzed oxidation of phenolic and indolic substrates that polymerize to yield melanins, which include eumelanin, pheomelanin, pyomelanin, and the allomelanins. The enzymes involved in melanin formation belong mainly to the tyrosinase and laccase protein families. The melanins are polymeric materials having applications in the pharmaceutical, cosmetic, optical, and electronic industries. The biotechnological production of these polymers is an attractive alternative to obtaining them by extraction from plant or animal material, where they are present at low concentrations. Several species of microorganisms have been identified as having a natural melanogenic capacity. The development and optimization of culture conditions with these organisms has resulted in processes for generating melanins. These processes are based on the conversion of melanin precursors present in the culture medium to the corresponding polymers. With the application of genetic engineering techniques, it has become possible to overexpress genes encoding enzymes involved in melanin formation, mostly tyrosinases, leading to an improvement in the productivity of melanogenic organisms, as well as allowing the generation of novel recombinant microbial strains that can produce diverse types of melanins. Furthermore, the metabolic engineering of microbial hosts by modifying pathways related to the supply of melanogenic precursors has resulted in strains with the capacity of performing the total synthesis of melanins from simple carbon sources in the scale of grams. In this review, the latest advances toward the generation of recombinant melanin production strains and production processes are summarized and discussed.

Highly Soluble Glimepiride and Irbesartan Co-amorphous Formulation with Potential Application in Combination Therapy

One-third of the population of the USA suffers from metabolic syndrome (MetS). Treatment of patients with MetS regularly includes drugs prescribed simultaneously to treat diabetes and cardiovascular diseases. Therefore, the development of novel multidrug formulations is recommended. However, the main problem with these drugs is their low solubility. The use of binary co-amorphous systems emerges as a promising strategy to increase drug solubility. In the present study, irbesartan (IBS) and glimepiride (GMP), class II active pharmaceutical ingredients (API), widely used in the treatment of arterial hypertension and diabetes, were selected to develop a novel binary co-amorphous system with remarkable enhancement in the dissolution of both APIs. The phase diagram of IBS-GMP was constructed and co-amorphous systems were prepared by melt-quench, in a wide range of compositions. Dissolution profile (studied at pH 1.2 and 37°C for mole fractions 0.01, 0.1, and 0.5) demonstrated that the x_GMP = 0.01 formulation presents the highest enhancement in its dissolution. GMP went from being practically insoluble to reach 3.9 ± 0.9 μg/mL, and IBS showed a 12-fold increment with respect to the dissolution of its crystalline form. Infrared studies showed that the increase in the dissolution profile is related to the intermolecular interactions (hydrogen bonds), which were dependent of composition. Results of structural and thermal characterization performed by XRD and DSC showed that samples have remained in amorphous state for more than 10 months of storage. This work contributes to the development of a highly soluble co-amorphous drugs with potential used in the treatment of MetS.

Long-Term Stability of New Co-Amorphous Drug Binary Systems: Study of Glass Transitions as a Function of Composition and Shelf Time

The amorphous state is of particular interest in the pharmaceutical industry due to the higher solubility that amorphous active pharmaceutical ingredients show compared to their respective crystalline forms. Due to their thermodynamic instability, drugs in the amorphous state tend to recrystallize; in order to avoid crystallization, it has been a common strategy to add a second component to hinder the crystalline state and form a thermally stable co-amorphous system, that is to say, an amorphous binary system which retains its amorphous structure. The second component can be a small molecule excipient (such as a sugar or an aminoacid) or a second drug, with the advantage that a second active pharmaceutical ingredient could be used for complementary or combined therapeutic purposes. In most cases, the compositions studied are limited to 1:1, 2:1 and 1:2 molar ratios, leaving a gap of information about phase transitions and stability on the amorphous state in a wider range of compositions. In the present work, a study of novel co–amorphous formulations in which the selection of the active pharmaceutical ingredients was made according to the therapeutic effect is presented. Resistance against crystallization and behavior of glass transition temperature (Tg were studied through calorimetric measurements as a function of composition and shelf time. It was found that binary formulations with Tg temperatures higher than those of pure components presented long-term thermal stability. In addition, significant increments of Tg values, of as much as 15 ∘C, were detected as a result of glass relaxation at room temperature during storage time; this behavior of glass transition has not been previously reported for co-amorphous drugs. Based on these results, it can be concluded that monitoring behavior of Tg and relaxation processes during the first weeks of storage leads to a more objective evaluation of the thermomechanical stability of an amorphous formulation.

Complex regulation of Hsf1-Skn7 activities by the catalytic subunits of PKA in Saccharomyces cerevisiae: experimental and computational evidences

Background

The cAMP-dependent protein kinase regulatory network (PKA-RN) regulates metabolism, memory, learning, development, and response to stress. Previous models of this network considered the catalytic subunits (CS) as a single entity, overlooking their functional individualities. Furthermore, PKA-RN dynamics are often measured through cAMP levels in nutrient-depleted cells shortly after being fed with glucose, dismissing downstream physiological processes.

Results

Here we show that temperature stress, along with deletion of PKA-RN genes, significantly affected HSE-dependent gene expression and the dynamics of the PKA-RN in cells growing in exponential phase. Our genetic analysis revealed complex regulatory interactions between the CS that influenced the inhibition of Hsf1/Skn7 transcription factors. Accordingly, we found new roles in growth control and stress response for Hsf1/Skn7 when PKA activity was low (cdc25Δ cells). Experimental results were used to propose an interaction scheme for the PKA-RN and to build an extension of a classic synchronous discrete modeling framework. Our computational model reproduced the experimental data and predicted complex interactions between the CS and the existence of a repressor of Hsf1/Skn7 that is activated by the CS. Additional genetic analysis identified Ssa1 and Ssa2 chaperones as such repressors. Further modeling of the new data foresaw a third repressor of Hsf1/Skn7, active only in theabsence of Tpk2. By averaging the network state over all its attractors, a good quantitative agreement between computational and experimental results was obtained, as the averages reflected more accurately the population measurements.

Conclusions

The assumption of PKA being one molecular entity has hindered the study of a wide range of behaviors. Additionally, the dynamics of HSE-dependent gene expression cannot be simulated accurately by considering the activity of single PKA-RN components (i.e., cAMP, individual CS, Bcy1, etc.). We show that the differential roles of the CS are essential to understand the dynamics of the PKA-RN and its targets. Our systems level approach, which combined experimental results with theoretical modeling, unveils the relevance of the interaction scheme for the CS and offers quantitative predictions for several scenarios (WT vs. mutants in PKA-RN genes and growth at optimal temperature vs. heat shock).

Electronic supplementary material

The online version of this article (doi:10.1186/s12918-015-0185-8) contains supplementary material, which is available to authorized users.

Production of cinnamic and p-hydroxycinnamic acid from sugar mixtures with engineered Escherichia coli

Background

The aromatic compounds cinnamic acid (CA) and p-hydroxycinnamic acid (pHCA) are used as flavoring agents as well as precursors of chemicals. These compounds are present in plants at low concentrations, therefore, complex purification processes are usually required to extract the product. An alternative production method for these aromatic acids is based on the use of microbial strains modified by metabolic engineering. These biotechnological processes are usually based on the use of simple sugars like glucose as a raw material. However, sustainable production processes should preferably be based on the use of waste material such as lignocellulosic hydrolysates.

Results

In this study, E. coli strains with active (W3110) and inactive phosphoenolpyruvate:sugar phosphotransferase system (PTS) (VH33) were engineered for CA and pHCA production by transforming them with plasmids expressing genes encoding phenylalanine/tyrosine ammonia lyase (PAL/TAL) enzymes from Rhodotorula glutinis or Arabidopsis thaliana as well as genes aroG^fbr and tktA, encoding a feedback inhibition resistant version of 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase and transketolase, respectively. The generated strains were evaluated in cultures with glucose, xylose or arabinose, as well as a simulated lignocellulosic hydrolysate containing a mixture of these three sugars plus acetate. Production of CA was detected in strains expressing PAL/TAL from A. thaliana, whereas both CA and pHCA accumulated in strains expressing the enzyme from R. glutinis. These experiments identified arabinose and W3110 expressing PAL/TAL from A. thaliana, aroG^fbr and tktA as the carbon source/strain combination resulting in the best CA specific productivity and titer. To improve pHCA production, a mutant with inactive pheA gene was generated, causing an 8-fold increase in the yield of this aromatic acid from the sugars in a simulated hydrolysate.

Conclusions

In this study the quantitative contribution of active or inactive PTS as well as expression of PAL/TAL from R. glutinis or A. thaliana were determined for production performance of CA and pHCA when growing on carbon sources derived from lignocellulosic hydrolysates. These data will be a useful resource in efforts towards the development of sustainable technologies for the production of aromatic acids.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-014-0185-1) contains supplementary material, which is available to authorized users.

Stabilization of amorphous paracetamol based systems using traditional and novel strategies

There is a special interest in having pharmaceutical active ingredients in the amorphous state due to their increased solubility and therefore, higher bioavailability. Nevertheless, not all of them present stable amorphous phases. In particular, paracetamol is an active ingredient widely known for its instability when prepared in the amorphous state. In the present work thermally stable amorphous binary paracetamol based systems were obtained showing stability on a wide range of temperatures: below its glass transition temperature (Tg) as amorphous solids in the glassy state and above their glass transition temperature, where these materials exist as stable supercooled liquids. To achieve stabilization of the binary paracetamol based system several strategies were applied and optimized, being the selection of the container material a key and novel approach to control the mechanical stress during cooling, eliminating cracks which act as nucleation centers leading to crystallization.

Global transcriptomic analysis of an engineered Escherichia coli strain lacking the phosphoenolpyruvate: carbohydrate phosphotransferase system during shikimic acid production in rich culture medium

BACKGROUND

Efficient production of SA in Escherichia coli has been achieved by modifying key genes of the central carbon metabolism and SA pathway, resulting in overproducing strains grown in batch- or fed-batch-fermentor cultures using a complex broth including glucose and YE. In this study, we performed a GTA to identify those genes significantly upregulated in an engineered E. coli strain, PB12.SA22, in mid EXP (5 h), early STA (STA1, 9 h), and late STA (STA2, 44 h) phases, grown in complex fermentation broth in batch-fermentor cultures.

RESULTS

Growth of E. coli PB12.SA22 in complex fermentation broth for SA production resulted in an EXP growth during the first 9 h of cultivation depending of supernatant available aromatic amino acids provided by YE because, when tryptophan was totally consumed, cells entered into a second, low-growth phase (even in the presence of glucose) until 26 h of cultivation. At this point, glucose was completely consumed but SA production continued until the end of the fermentation (50 h) achieving the highest accumulation (7.63 g/L of SA). GTA between EXP/STA1, EXP/STA2 and STA1/STA2 comparisons showed no significant differences in the regulation of genes encoding enzymes of central carbon metabolism as in SA pathway, but those genes encoding enzymes involved in sugar, amino acid, nucleotide/nucleoside, iron and sulfur transport; amino acid catabolism and biosynthesis; nucleotide/nucleoside salvage; acid stress response and modification of IM and OM were upregulated between comparisons.

CONCLUSIONS

GTA during SA production in batch-fermentor cultures of strain PB12.SA22 grown in complex fermentation broth during the EXP, STA1 and STA2 phases was studied. Significantly, upregulated genes during the EXP and STA1 phases were associated with transport, amino acid catabolism, biosynthesis, and nucleotide/nucleoside salvage. In STA2, upregulation of genes encoding transporters and enzymes involved in the synthesis and catabolism of Arg suggests that this amino acid could have a key role in the fuelling of carbon toward SA synthesis, whereas upregulation of genes involved in pH stress response, such as membrane modifications, suggests a possible response to environmental conditions imposed on the cell at the end of the fermentation.

A novel plasmid vector designed for chromosomal gene integration and expression: use for developing a genetically stable Escherichia coli melanin production strain

Recombinant Escherichia coli strains for the production of valuable products are usually generated by transformation with plasmid expression vectors. However, in spite of their usefulness, common problems associated with plasmid use include segregrational and structural instability as well as undesired copy-number effects. A viable alternative to plasmid use is chromosomal gene integration. With the purpose of facilitating the process of stable strain generation, a novel chromosomal integration vector was developed and tested. We describe the construction and use of novel expression vector pLoxGentrc that contains the strong trc promoter (P(trc)), a multiple cloning site, the T1 and T2 rrnB terminator sequences, the lacI(q) gene and the aacC1 gene conferring gentamicin resistance flanked by two loxP sites. As a demonstration of utility, melanin-producing strains of E. coli were generated employing this vector. Melanin is a polymer synthesized by the enzyme tyrosinase using l-tyrosine as substrate. The melA gene encoding a tyrosinase from Rhizobium etli was ligated to pLoxGentrc to generate pLoxGentrcmelA. This plasmid was transformed into E. coli W3110 to generate a melanin-producing strain. A region from this plasmid including P(trc)melA, T1 and T2 rrnB and the aacC1 gene was amplified by PCR employing primers with 45 b regions of homology to the lacZ gene. The PCR product was electroporated into strain W3110 that expressed the λ-Red enzymes. From this experiment, strain W3110P(tr)(c)melA, was obtained having the melA gene inserted in the lacZ locus. Fermentor cultures with strain W3110/pLoxGentrcmelA grown in the presence and absence of gentamicin as well as W3110P(tr)(c)melA without antibiotic revealed that the latter displays high genetic stability as well as the highest melanin titer. Vector pLoxGentrc should be useful during strain generation processes, enabling direct comparison of plasmid and chromosome-based production systems.

El impacto tecnológico sobre los procesos migratorios: los locutorios, ¿sólo espacios tecnológicos?

El estudio del impacto de las TIC en la conceptualización y vivencia de los procesos migratorios despierta un creciente interés en las ciencias sociales. En este marco, nuestro trabajo aborda la pregunta por el papel de los locutorios en la conformación de la experiencia migratoria. Lo más visible en estos espacios son las tecnologías y las relaciones que mediante éstas se establecen con el lugar de origen. Sin embargo, las tecnologías que contiene el locutorio no tienen sentido por sí solas; es necesario ubicarlas en su contexto de uso, examinando la red de prácticas sociales en las que se insertan y que les dan sentido. Argumentamos que la clave no está en preguntarse cómo las tecnologías impactan en la experiencia migratoria, sino en preguntarse por las dinámicas que se generan en el interior los locutorios y por las apropiaciones que los/as usuarios/as hacen de estos espacios y de las tecnologías.

Role of HSP101 in the stimulation of nodal root development from the coleoptilar node by light and temperature in maize (Zea mays L.) seedlings

Nodal roots (NRs) constitute the prevalent root system of adult maize plants. NRs emerge from stem nodes located below or above ground, and little is known about their inducing factors. Here, it is shown that precocious development of NRs at the coleoptilar node (NRCNs) occurred in maize seedlings when: (i) dark grown and stimulated by the concurrent action of a single light shock of low intensity white light (2 μmol m(-2) s(-1)) and a single heat shock; (ii) grown under a photoperiod of low intensity light (0.1 μmol m(-2) s(-1)); or (iii) grown in the dark under a thermoperiod (28 °C/34 °C). The light shock effects were synergistic with heat shock and with the photoperiod, whereas the thermoperiodical and photoperiodical effects were additive. Dissection of the primary root or the root cap, to mimic the fatal consequences of severe heat shock, caused negligible effects on NRCN formation, indicating that the shoot is directly involved in perception of the heat shock-inducible signal that triggered NRCN formation. A comparison between hsp101-m5::Mu1/hsp101-m5::Mu1 and Hsp101/Hsp101 seedlings indicated that the heat shock protein 101 (HSP101) chaperone inhibited NRCN formation in the light and in the dark. Stimulation of precocious NRCN formation by light and heat shocks was affected by genetic background and by the stage of seedling development. HSP101 protein levels increased in the coleoptilar node of induced wild-type plants, particularly in the procambial region, where NRCN formation originated. The adaptive relevance of development of NRCNs in response to these environmental cues and hypothetical mechanisms of regulation by HSP101 are discussed.

Small heat-shock proteins and leaf cooling capacity account for the unusual heat tolerance of the central spike leaves in Agave tequilana var. Weber

Agaves are perennial crassulacean acid metabolism (CAM) plants distributed in tropical and subtropical arid environments, features that are attractive for studying the heat-shock response. In agaves, the stress response can be analysed easily during leaf development, as they form a spirally shaped rosette, having the meristem surrounded by folded leaves in the centre (spike) and the unfolded and more mature leaves in the periphery. Here, we report that the spike of Agave tequilana is the most thermotolerant part of the rosette withstanding shocks of up to 55 degrees C. This finding was inconsistent with the patterns of heat-shock protein (Hsp) gene expression, as maximal accumulation of Hsp transcripts was at 44 degrees C in all sectors (spike, inner, middle and outer). However, levels of small HSP (sHSP)-CI and sHSP-CII proteins were conspicuously higher in spike leaves at all temperatures correlating with their thermotolerance. In addition, spike leaves showed a higher stomatal density and abated more efficiently their temperature several degrees below that of air. We propose that the greater capacity for leaf cooling during the day in response to heat stress, and the elevated levels of sHSPs, constitute part of a set of strategies that protect the SAM and folded leaves of A. tequilana from high temperatures.

A geometric morphometric analysis of hominin upper first molar shape

Recent studies have revealed interesting differences in upper first molar morphology across the hominin fossil record, particularly significant between H. sapiens and H. neanderthalensis. Usually these analyses have been performed by means of classic morphometric methods, including the measurement of relative cusp areas or the angles defined between cusps. Although these studies have provided valuable information for the morphological characterization of some hominin species, we believe that the analysis of this particular tooth could be more conclusive for taxonomic assignment. In this study, we have applied geometric morphometric methods to explore the morphological variability of the upper first molar (M(1)) across the human fossil record. Our emphasis focuses on the study of the phenetic relationships among the European middle Pleistocene populations (designated as H. heidelbergensis) with H. neanderthalensis and H. sapiens, but the inclusion of Australopithecus and early Homo specimens has helped us to assess the polarity of the observed traits. H. neanderthalensis presents a unique morphology characterized by a relatively distal displacement of the lingual cusps and protrusion in the external outline of a large and bulging hypocone. This morphology can be found in a less pronounced degree in the European early and middle Pleistocene populations, and reaches its maximum expression with the H. neanderthalensis lineage. In contrast, modern humans retain the primitive morphology with a square occlusal polygon associated with a round external outline.

New roles for CDC25 in growth control, galactose regulation and cellular differentiation in Saccharomyces cerevisiae

Living organisms display large differences in stress resistance throughout their life cycles. To study the coordinated regulation of development and stress responses in exponentially growing yeast, mutants that displayed elevated heat-shock resistance at this stage were screened for. Here, two new mutant alleles of CDC25 in Saccharomyces cerevisiae, cdc25-21 and cdc25-22, are described. During exponential growth in glucose at 25 degrees C, these mutants are resistant to heat, oxidative, osmotic and ionic shock, accumulate stress-protein transcripts, show slow growth rates, thick cell walls and glycogen hyperaccumulation and lack cAMP signalling in response to glucose. Genetic and cellular analyses revealed that the stationary-phase phenotypes of cdc25-21 and cdc25-22 mutants are not due to entrance to a G(0) state during exponential growth, but are the result of a prolonged G(1) phase. It was found that, in the W303 background, CDC25 is dispensable for growth in glucose media. However, CDC25 is essential for growth in galactose, in non-fermentable carbon sources and under continuous incubation at 38 degrees C. In conclusion, the function of the catalytic, C-terminal domain of Cdc25p is not only important for fermentative growth, but also for growth in non-fermentable carbon sources and to trigger galactose derepression.

Cap-independent translation of maize Hsp101

Maize embryonic axes contain stored mRNAs, some of which are able to undergo cap-independent translation initiation during germination. The Hsp101 mRNA, encoding a heat shock protein, is essential for thermo-tolerance induction and is present among the stored transcripts. This research aimed to investigate whether the Hsp101 transcript is IRES-driven regulated upon heat stress. Hsp101 transcribed either in vitro or in vivo was efficiently translated via a cap-independent mechanism. This was observed either in an animal in vitro translation system containing proteolytically cleaved eukaryotic initiation factor eIF4G or in a plant system lacking both eIF4E and eIFiso4E initiation factors. Deletion of the 5' untranslated region (UTR) from the Hsp101 mRNA abolished its cap-independent translation indicating that this nucleotide sequence is required to confer cap-independent initiation. Bicistronic constructs containing the Hsp101 mRNA 5'UTR in sense and anti-sense directions between two reporter genes were translated in both cap-independent systems. A similar bicistronic construct containing a viral internal ribosome entry site (IRES) element between the reporter genes was used as control. Internal translation of the second reporter gene was observed when the Hsp101 5'UTR was in the sense but not in the anti-sense orientation in the bicistronic construct. Taken together, these data suggest that the 5'UTR of maize Hsp101, a plant cellular mRNA, functions as an IRES-like element accounting for its cap-independent translation during heat stress.

Error rates in buccal-dental microwear quantification using scanning electron microscopy

Dental microwear, usually analyzed using scanning electron microscopy (SEM) techniques, is a good indicator of the abrasive potential of past human population diets. Scanning electron microscopy secondary electrons provide excellent images of dental enamel relief for characterizing striation density, average length, and orientation. However, methodological standardization is required for interobserver comparisons since semiautomatic counting procedures are still used for micrograph characterization. The analysis of normally distributed variables allows the characterization of small interpopulation differences. However, the interobserver error rates associated with SEM experience and the degree of expertise in measuring striations are critical to population dietary interpretation. The interobserver comparisons made here clearly indicate that the precision of SEM buccal microwear measurements depends heavily on variable definition and the researcher's expertise. Moreover, error rates are not the only concern for dental microwear research. Low error rates do not guarantee that all researchers are measuring the same magnitudes of the variables considered. The results obtained show that researchers tend to maintain high intrapopulation homogeneity and low measurement error rates, whereas significant interobserver differences appear. Such differences are due to a differential interpretation of SEM microwear features and variable definitions that require detailed and precise agreement among researchers. The substitution of semiautomatic with fully automated procedures will completely avoid interobserver error rate differences.

Maize HSP101 plays important roles in both induced and basal thermotolerance and primary root growth

HSP101 belongs to the ClpB protein subfamily whose members promote the renaturation of protein aggregates and are essential for the induction of thermotolerance. We found that maize HSP101 accumulated in mature kernels in the absence of heat stress. At optimal temperatures, HSP101 disappeared within the first 3 days after imbibition, although its levels increased in response to heat shock. In embryonic cells, HSP101 concentrated in the nucleus and in some nucleoli. Hsp101 maps near the umc132 and npi280 markers on chromosome 6. Five maize hsp101-m-::Mu1 alleles were isolated. Mutants were null for HSP101 and defective in both induced and basal thermotolerance. Moreover, during the first 3 days after imbibition, primary roots grew faster in the mutants at optimal temperature. Thus, HSP101 is a nucleus-localized protein that, in addition to its role in thermotolerance, negatively influences the growth rate of the primary root. HSP101 is dispensable for proper embryo and whole plant development in the absence of heat stress.

Characterization of a maize heat-shock protein 101 gene, HSP101, encoding a ClpB/Hsp100 protein homologue

Heat shock protein 101 (HSP101) cDNA and genomic clones from maize have been isolated. The structure of maize HSP101 reveals the presence of six exons interrupted by five introns. Maize HSP101 contains a predicted open reading frame that translates into a 912-aa sequence with a mass of 101kDa. Initiation of transcription was mapped 146 bases upstream of the AUG codon. Five heat shock element (HSE) boxes were found within the proximal 289 bases of the promoter region. Southern blot analysis of genomic DNA indicates that the maize genome contains only one copy of HSP101. A protein sequence comparison showed that maize Hsp101 belongs to the heat shock 100kDa and caseino-lytic protease B protein family (Hsp100/ClpB) that plays important roles in bacteria and yeast in the survival to extremely high temperatures and the control of proteolysis. Accumulation of HSP101 mRNA was strong under heat shock conditions, but not detectable after cold or osmotic stress treatments or by exogenous application of ABA. The analysis of the predicted supersecondary structure of maize Hsp101 showed that a coiled-coil located in the middle region of the protein is evolutionarily conserved in all members of the Clp A, B and C subfamilies. It is proposed that these supersecondary structures may have important roles in Clp function.

A Neurospora crassa mutant altered in the regulation of L-amino acid oxidase

The isolation and characterization of a Neurospora crassa mutant altered in L-amino oxidase regulation is reported. The previously isolated gln-1bR8 strain, which only synthesizes the glutamine synthetase alpha monomer and lacks the beta monomer, was used as parental strain. A mutant derivative of strain was selected for its ability to grow on minimal medium in the presence of DL-methionine-SR-sulfoximine (MSO), an inhibitor of glutamine synthetase activity. This gln-1bR8;MSOR mutant overcame the inhibitory effect of MSO by increasing the activity of L-amino acid oxidase, an enzyme capable of degrading this compound. In contrast with the wild-type strain, the L-amino acid oxidase of the MSOR mutant was resistant to glutamine repression; in fact, it was induced by this amino acid but repressed by ammonium. This mutant is different from other nitrogen regulatory N. crassa mutants reported and is only altered in the regulation of L-amino acid oxidase. The MSOR mutation is epistatic to nit-2 since the nit2;MSOR double mutant regulated the L-amino acid oxidase in the same way as the MSOR single mutant.

Regulation of ammonium ion assimilation enzymes in Neurospora crassa nit-2 and ms-5 mutant strains

In Neurospora crassa the nit-2 and nmr-1 (ms-5) loci represent the major control genes encoding regulatory proteins that allow the coordinated expression of various systems involved with the utilization of a secondary nitrogen source. In this paper we examined the effect of the nit-2 and ms-5 (nmr-1 locus) mutations on the regulation of the ammonium assimilation enzymes, glutamine synthetase and glutamate dehydrogenase, which are regulated by the products of these genes; however, glutamate synthase is not so regulated. Glutamine synthetase and glutamate dehydrogenase levels are also regulated by the amino nitrogen content. We present evidence that the ms-5 and glnr strains, which behave very similarly in their resistance to glutamine repression, are different and map in different loci.