Vesicle-associated membrane protein of Arabidopsis suppresses Bax-induced apoptosis in yeast downstream of oxidative burst

Vesicle formation-related protein CaSec16 and its ankyrin protein partner CaANK2B jointly enhance salt tolerance in pepper

Vesicle transport plays important roles in plant tolerance against abiotic stresses. However, the contribution of a vesicle formation related protein CaSec16 (COPII coat assembly protein Sec16-like) in pepper tolerance to salt stress remains unclear. In this study, we report that the expression of CaSec16 was upregulated by salt stress. Compared to the control, the salt tolerance of pepper with CaSec16-silenced was compromised, which was shown by the corresponding phenotypes and physiological indexes, such as the death of growing point, the aggravated leaf wilting, the higher increment of relative electric leakage (REL), the lower content of total chlorophyll, the higher accumulation of dead cells, H2O2, malonaldehyde (MDA), and proline (Pro), and the inhibited induction of marker genes for salt-tolerance and vesicle transport. In contrast, the salt tolerance of pepper was enhanced by the transient overexpression of CaSec16. In addition, heterogeneously induced CaSec16 protein did not enhance the salt tolerance of Escherichia coli, an organism lacking the vesicle transport system. By yeast two-hybrid method, an ankyrin protein, CaANK2B, was identified as the interacting protein of CaSec16. The expression of CaANK2B showed a downward trend during the process of salt stress. Compared with the control, pepper plants with transient-overexpression of CaANK2B displayed increased salt tolerance, whereas those with CaANK2B-silenced exhibited reduced salt tolerance. Taken together, both the vesicle formation related protein CaSec16 and its interaction partner CaANK2B can improve the pepper tolerance to salt stress.

Genome-Scale Identification, in Silico Characterization and Interaction Study Between Wheat SNARE and NPSN Gene Families Involved in Vesicular Transport

Wheat is an important cereal crop grown worldwide but it's yield is severely affected by various biotic and abiotic stresses. SNAREs are key regulators of vesicle trafficking and are present in abundance in higher plant species suggesting their prominence in growth and development. Novel Plant SNAREs (NPSN) are found exclusively in plants. Hence, a comprehensive analysis of these two gene families in wheat genome was accomplished in this study. We report here 27 SNAREs and eight NPSN genes. These genes and their respective proteins were investigated for gene structure, physiochemical properties, domain and motif architecture, phylogeny, chromosomal localization and possible interactions. Phylogenetic and motif analysis confirmed SNARE domain in all the proteins. Functional annotation revealed participation in biological process like vesicle fusion, exocytosis, protein targeting to vacuole and SNAP receptor activity. At subcellular level, SNAREs were localized in multiple organelles whereas NPSN proteins were localized in cytoplasm where they regulate vesicle fusion. The 3-D structures built with Modeller proved the presence of SNARE motifs in the identified proteins. Possible protein-protein interactions between SNARE and NPSN proteins were determined and docking was performed. The results augmented our understanding about molecular function, evolutionary relation, location inside the cell and their interactions.

Lepidium sativum and Its Biogenic Silver Nanoparticles Activate Immune Cells and Induce Apoptosis and Cell Cycle Arrest in HT-29 Colon Cancer Cells

There is an increased demand for plants with antioxidants and anticancer properties. Lepidium sativum L. is an edible plant with medical importance. In this study, we aimed to investigate the anticancer activity; antioxidant capacity and antibacterial impact of Lepidium sativum L. seed acetone extract (LSSAExt), alone and with its biogenic silver nanoparticles (AgNPs). LSSAExt-produced AgNPs were characterized using SEM, XRD and Vis/UV analysis. Biomolecules in LSSAExt and LSSAExt + AgNPs were explored utilizing FTIR. The ability of LSSAExt and LSSAExt + AgNPs to induce apoptosis and mitotic cell arrest in the HT-29 colon cancer cells, compared to normal and repeated cell division activated splenic cells was determined by florescent stains and flow cytometry. Antibacterial power was tested using well diffusion technique. LSSAExt and LSSAExt + AgNPs showed a good antibacterial impact. LSSAExt contains ROS, which could help in cancer cells apoptosis. LSSAExt and LSSAExt+AgNPs were not toxic to splenic cells and increased the rate of their cell division. LSSAExt and LSSAExt+AgNPs increased p53 expression and could arrest cell division of HT-29 colon cancer cells but not of normal fast dividing cells. LSSAExt and LSSAExt+AgNPs caused apoptosis in cancer cells rather than necrosis. In conclusion, acetone preparation of the edible plant L. sativum is a good antibacterial agent, good anticancer preparation at least against colon cancer as it is shown to be targeted, effective and can boost immune cells.

Human VAMP3 Suppresses or Negatively Regulates Bax Induced Apoptosis in Yeast

Apoptosis is an essential process that is regulated genetically and could lead to a serious disease condition if not well controlled. Bax is one of the main proapoptotic proteins and actively involved in programmed cell death. It has been suggested that Bax induced apoptosis in yeast could be obstructed by enhancing vesicular membrane trafficking. Plasma membrane proteins and lipid oxidation were reduced by a vesicle-associated membrane protein (VAMP) when expressed in yeast, suggesting its potential role in repairing membranes. Membrane integrity is crucial, as the loss of membrane integrity will result in the leakage of ions from mitochondria, and ultimately cell death due to overproduction of reactive oxygen species (ROS). Expression of Arabidopsis’ VAMP has been linked to antiapoptosis activity. Since plant VAMP has been associated with antiapoptotic activities, this study investigates the possible participation of human VAMP3 in blocking human Bax mediated apoptosis. Some novel genes were identified to rescue Bax’s proapoptotic effects, in a yeast-based human hippocampal cDNA library screen. VAMP3 (a gene code for proteins involved in protein secretion) gene was chosen for further study to confirm its role in inhibiting apoptosis. VAMP3 was coexpressed with a chromosomally integrated Bax gene expression cassette driven by the GAL1 promoter. The antiapoptotic proteins of the Bcl-2 family (Bcl xL) were known to negate the proapoptotic properties of Bax. However, the new gene (VAMP3) results show that novel antiapoptotic proteins can be identified using a yeast-based assay. The findings presented here show that human VAMP3 protein has antiapoptotic property and could abrogate Bax induced apoptosis (cell death).

Aegeline, a natural product from the plant Aegle marmelos, mimics the yeast SNARE protein Sec22p in suppressing α-synuclein and Bax toxicity in yeast

Herein, we have identified yeast Sec22p (ySec22p), a SNARE protein essential for endoplasmic reticulum to Golgi trafficking, as a suppressor of Bax-induced yeast apoptosis and corroborated published observations that ySec22p suppresses α-synuclein's toxicity in yeast. It has been suggested that compounds which enhance expression, in neurons, of human homologues of ySec22p (Sec22Bp/Sec22p/Sec22A) would prevent synucleinopathies, such as Parkinson's disease. With the aim of finding a small molecule that would mimic ySec22p, a library of natural products consisting of 394-compounds was screened using yeast cells that express either human α-synuclein or human Bax. The antioxidant aegeline, an alkaloid-amide occurring in the leaves of the plant Aegle marmelos Correa, was the only molecule that overcame apoptosis induced by both α-synuclein and Bax in yeast. Besides, aegeline also prevented growth block in cells expressing the more toxic A53T α-synuclein mutant. Restoration of cell growth occurred through inhibition of increased ROS levels, mitochondrial membrane potential loss and nuclear DNA fragmentation, characteristics of apoptosis manifested in α-synuclein or Bax-expressing cells. These results highlight the importance of yeast systems to identify rapidly molecules that may prevent the onset of apoptosis that occurs in Parkinson's disease.

Gene encoding vesicle-associated membrane protein-associated protein from Triticum aestivum (TaVAP) confers tolerance to drought stress

Abiotic stresses like drought, salinity, high and low temperature, and submergence are major factors that limit the crop productivity. Hence, identification of genes associated with stress response in crops is a prerequisite for improving their tolerance to adverse environmental conditions. In an earlier study, we had identified a drought-inducible gene, vesicle-associated membrane protein-associated protein (TaVAP), in developing grains of wheat. In this study, we demonstrate that TaVAP is able to complement yeast and Arabidopsis mutants, which are impaired in their respective orthologs, signifying functional conservation. Constitutive expression of TaVAP in Arabidopsis imparted tolerance to water stress conditions without any apparent yield penalty. Enhanced tolerance to water stress was associated with maintenance of higher relative water content, photosynthetic efficiency, and antioxidant activities. Compared to wild type, the TaVAP-overexpressing plants showed enhanced lateral root proliferation that was attributed to higher endogenous levels of IAA. These studies are the first to demonstrate that TaVAP plays a critical role in growth and development in plants, and is a potential candidate for improving the abiotic stress tolerance in crop plants.

Ectopic expression of PgRab7 in rice plants (Oryza sativa L.) results in differential tolerance at the vegetative and seed setting stage during salinity and drought stress

In this work, we have overexpressed a vesicle trafficking protein, Rab7, from a stress-tolerant plant, Pennisetum glaucum, in a high-yielding but stress-sensitive rice variety Pusa Basmati-1 (PB-1). The transgenic rice plants were tested for tolerance against salinity and drought stress. The transgenic plants showed considerable tolerance at the vegetative stage against both salinity (200 mM NaCl) and drought stress (up to 12 days after withdrawing water). The protection against salt and drought stress may be by regulating Na⁺ ion homeostasis, as the transgenic plants showed altered expression of multiple transporter genes, including OsNHX1, OsNHX2, OsSOS1, OsVHA, and OsGLRs. In addition, decreased generation and maintenance of lesser reactive oxygen species (ROS), with maintenance of chloroplast grana and photosynthetic machinery was observed. When evaluated for reproductive growth, 89-96 % of seed setting was maintained in transgenic plants during drought stress; however, under salt stress, a 33-53 % decrease in seed setting was observed. These results indicate that PgRab7 overexpression in rice confers differential tolerance at the seed setting stage during salinity and drought stress and could be a favored target for raising drought-tolerant crops.

TaSYP71, a Qc-SNARE, Contributes to Wheat Resistance against Puccinia striiformis f. sp. tritici

N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) are involved in plant resistance; however, the role of SYP71 in the regulation of plant-pathogen interactions is not well known. In this study, we characterized a plant-specific SNARE in wheat, TaSYP71, which contains a Qc-SNARE domain. Three homologs are localized on chromosome 1AL, 1BL, and 1DL. Using Agrobacterium-mediated transient expression, TaSYP71 was localized to the plasma membrane in Nicotiana benthamiana. Quantitative real-time PCR assays revealed that TaSYP71 homologs was induced by NaCl, H2O2 stress and infection by virulent and avirulent Puccinia striiformis f. sp. tritici (Pst) isolates. Heterologous expression of TaSYP71 in Schizosaccharomyces pombe elevated tolerance to H2O2. Meanwhile, H2O2 scavenging gene (TaCAT) was downregulated in TaSYP71 silenced plants treated by H2O2 compared to that in control, which indicated that TaSYP71 enhanced tolerance to H2O2 stress possibly by influencing the expression of TaCAT to remove the excessive H2O2 accumulation. When TaSYP71 homologs were all silenced in wheat by the virus-induced gene silencing system, wheat plants were more susceptible to Pst, with larger infection area and more haustoria number, but the necrotic area of wheat mesophyll cells were larger, one possible explanation that minor contribution of resistance to Pst was insufficient to hinder pathogen extension when TaSYP71 were silenced, and the necrotic area was enlarged accompanied with the pathogen growth. Of course, later cell death could not be excluded. In addition, the expression of pathogenesis-related genes were down-regulated in TaSYP71 silenced wheat plants. These results together suggest that TaSYP71 play a positive role in wheat defense against Pst.

Subcellular localization and trafficking of phytolongins (non-SNARE longins) in the plant secretory pathway

SNARE proteins are central elements of the machinery involved in membrane fusion of eukaryotic cells. In animals and plants, SNAREs have diversified to sustain a variety of specific functions. In animals, R-SNARE proteins called brevins have diversified; in contrast, in plants, the R-SNARE proteins named longins have diversified. Recently, a new subfamily of four longins named 'phytolongins' (Phyl) was discovered. One intriguing aspect of Phyl proteins is the lack of the typical SNARE motif, which is replaced by another domain termed the 'Phyl domain'. Phytolongins have a rather ubiquitous tissue expression in Arabidopsis but still await intracellular characterization. In this study, we found that the four phytolongins are distributed along the secretory pathway. While Phyl2.1 and Phyl2.2 are strictly located at the endoplasmic reticulum network, Phyl1.2 associates with the Golgi bodies, and Phyl1.1 locates mainly at the plasma membrane and partially in the Golgi bodies and post-Golgi compartments. Our results show that export of Phyl1.1 from the endoplasmic reticulum depends on the GTPase Sar1, the Sar1 guanine nucleotide exchange factor Sec12, and the SNAREs Sec22 and Memb11. In addition, we have identified the Y48F49 motif as being critical for the exit of Phyl1.1 from the endoplasmic reticulum. Our results provide the first characterization of the subcellular localization of the phytolongins, and we discuss their potential role in regulating the secretory pathway.

Phenotypic and genetic evidence for ecological speciation of Aquilegia japonica and A. oxysepala

Natural selection is thought to be a driving force that can cause the evolution of reproductive isolation. The genus Aquilegia is a model system to address how natural selection promotes the process of speciation. Morphological differences between A. oxysepala, A. japonica and their hybrids were quantified for two vegetative (plant height and leaf area) and three floral morphological (sepal area, corolla length and diameter) traits. We also evaluated the genetic variability of the two species and their hybrids based on two chloroplast (1225 bp), four nuclear (5811 bp) genes and 15 microsatellites. Our results revealed that differentiation of A. japonica and A. oxysepala at the ecological and morphological levels also involved divergence at the genetic level. In addition, the analysis of nucleotide variation patterns showed that the two species possessed numerous fixation sites at nuclear genes gAA4, gA7 and gAA12. Furthermore, we found that all of the phenotypic hybrids also showed a genetically admixed ancestry. These findings suggest that natural selection has indeed facilitated the formation of distinct genetic variation patterns in the two Aquilegia species and habitat adaptation has been driving the ecologically based evolution of reproductive isolation.

Effect of Aluminum Treatment on Proteomes of Radicles of Seeds Derived from Al-Treated Tomato Plants

Aluminum (Al) toxicity is a major constraint to plant growth and crop yield in acid soils. Tomato cultivars are especially susceptible to excessive Al³⁺ accumulated in the root zone. In this study, tomato plants were grown in a hydroponic culture system supplemented with 50 µM AlK(SO₄)₂. Seeds harvested from Al-treated plants contained a significantly higher Al content than those grown in the control hydroponic solution. In this study, these Al-enriched tomato seeds (harvested from Al-treated tomato plants) were germinated in 50 µM AlK(SO₄)₂ solution in a homopiperazine-1,4-bis(2-ethanesulfonic acid) buffer (pH 4.0), and the control solution which contained the buffer only. Proteomes of radicles were analyzed quantitatively by mass spectrometry employing isobaric tags for relative and absolute quantitation (iTRAQ^®). The proteins identified were assigned to molecular functional groups and cellular metabolic pathways using MapMan. Among the proteins whose abundance levels changed significantly were: a number of transcription factors; proteins regulating gene silencing and programmed cell death; proteins in primary and secondary signaling pathways, including phytohormone signaling and proteins for enhancing tolerance to abiotic and biotic stress. Among the metabolic pathways, enzymes in glycolysis and fermentation and sucrolytic pathways were repressed. Secondary metabolic pathways including the mevalonate pathway and lignin biosynthesis were induced. Biological reactions in mitochondria seem to be induced due to an increase in the abundance level of mitochondrial ribosomes and enzymes in the TCA cycle, electron transport chains and ATP synthesis.

Overexpression of a Vesicle Trafficking Gene, OsRab7, enhances salt tolerance in rice

High soils salinity is a main factor affecting agricultural production. Studying the function of salt-tolerance-related genes is essential to enhance crop tolerance to stress. Rab7 is a small GTP-binding protein that is distributed widely among eukaryotes. Endocytic trafficking mediated by Rab7 plays an important role in animal and yeast cells, but the current understanding of Rab7 in plants is still very limited. Herein, we isolated a vesicle trafficking gene, OsRab7, from rice. Transgenic rice over-expressing OsRab7 exhibited enhanced seedling growth and increased proline content under salt-treated conditions. Moreover, an increased number of vesicles was observed in the root tip of OsRab7 transgenic rice. The OsRab7 over-expression plants showed enhanced tolerance to salt stress, suggesting that vacuolar trafficking is important for salt tolerance in plants.

Chromium stress response effect on signal transduction and expression of signaling genes in rice

Hexavalent chromium [Cr(VI)] is a non-essential metal for normal plants and is toxic to plants at high concentrations. However, signaling pathways and molecular mechanisms of its action on cell function and gene expression remain elusive. In this study, we found that Cr(VI) induced endogenous reactive oxygen species (ROS) generation and Ca(2+) accumulation and activated NADPH oxidase and calcium-dependent protein kinase. We investigated global transcriptional changes in rice roots by microarray analysis. Gene expression profiling indicated activation of abscisic acid-, ethylene- and jasmonic acid-mediated signaling and inactivation of gibberellic acid-related pathways in Cr(VI) stress-treated rice roots. Genes encoding signaling components such as the protein kinases domain of unknown function 26, receptor-like cytoplasmic kinase, LRK10-like kinase type 2 and protein phosphatase 2C, as well as transcription factors WRKY and apetala2/ethylene response factor were predominant during Cr(VI) stress. Genes involved in vesicle trafficking were subjected to functional characterization. Pretreating rice roots with a vesicle trafficking inhibitor, brefeldin A, effectively reduced Cr(VI)-induced ROS production. Suppression of the vesicle trafficking gene, Exo70, by virus-induced gene silencing strategies revealed that vesicle trafficking is required for mediation of Cr(VI)-induced ROS production. Taken together, these findings shed light on the molecular mechanisms in signaling pathways and transcriptional regulation in response to Cr stress in plants.

Loss of the Arabidopsis thaliana P₄-ATPase ALA3 reduces adaptability to temperature stresses and impairs vegetative, pollen, and ovule development

Members of the P₄ subfamily of P-type ATPases are thought to help create asymmetry in lipid bilayers by flipping specific lipids between the leaflets of a membrane. This asymmetry is believed to be central to the formation of vesicles in the secretory and endocytic pathways. In Arabidopsis thaliana, a P₄-ATPase associated with the trans-Golgi network (ALA3) was previously reported to be important for vegetative growth and reproductive success. Here we show that multiple phenotypes for ala3 knockouts are sensitive to growth conditions. For example, ala3 rosette size was observed to be dependent upon both temperature and soil, and varied between 40% and 80% that of wild-type under different conditions. We also demonstrate that ala3 mutants have reduced fecundity resulting from a combination of decreased ovule production and pollen tube growth defects. In-vitro pollen tube growth assays showed that ala3 pollen germinated ∼2 h slower than wild-type and had approximately 2-fold reductions in both maximal growth rate and overall length. In genetic crosses under conditions of hot days and cold nights, pollen fitness was reduced by at least 90-fold; from ∼18% transmission efficiency (unstressed) to less than 0.2% (stressed). Together, these results support a model in which ALA3 functions to modify endomembranes in multiple cell types, enabling structural changes, or signaling functions that are critical in plants for normal development and adaptation to varied growth environments.

Plant defense mechanisms are activated during biotrophic and necrotrophic development of Colletotricum graminicola in maize

Hemibiotrophic plant pathogens first establish a biotrophic interaction with the host plant and later switch to a destructive necrotrophic lifestyle. Studies of biotrophic pathogens have shown that they actively suppress plant defenses after an initial microbe-associated molecular pattern-triggered activation. In contrast, studies of the hemibiotrophs suggest that they do not suppress plant defenses during the biotrophic phase, indicating that while there are similarities between the biotrophic phase of hemibiotrophs and biotrophic pathogens, the two lifestyles are not analogous. We performed transcriptomic, histological, and biochemical studies of the early events during the infection of maize (Zea mays) with Colletotrichum graminicola, a model pathosystem for the study of hemibiotrophy. Time-course experiments revealed that mRNAs of several defense-related genes, reactive oxygen species, and antimicrobial compounds all begin to accumulate early in the infection process and continue to accumulate during the biotrophic stage. We also discovered the production of maize-derived vesicular bodies containing hydrogen peroxide targeting the fungal hyphae. We describe the fungal respiratory burst during host infection, paralleled by superoxide ion production in specific fungal cells during the transition from biotrophy to a necrotrophic lifestyle. We also identified several novel putative fungal effectors and studied their expression during anthracnose development in maize. Our results demonstrate a strong induction of defense mechanisms occurring in maize cells during C. graminicola infection, even during the biotrophic development of the pathogen. We hypothesize that the switch to necrotrophic growth enables the fungus to evade the effects of the plant immune system and allows for full fungal pathogenicity.

Over-expression of a Rab family GTPase from phreatophyte Prosopis juliflora confers tolerance to salt stress on transgenic tobacco

Plant growth and productivity are adversely affected by various abiotic and biotic stress factors. In our previous study, we used Prosopis juliflora, an abiotic stress tolerant tree species of Fabaceae, as a model plant system for isolating genes functioning in abiotic stress tolerance. Here we report the isolation and characterization of a Rab family GTPase from P. juliflora (Pj Rab7) and the ability of this gene to confer salt stress tolerance in transgenic tobacco. Northern analysis for Pj Rab7 in P. juliflora leaf tissue revealed up-regulation of this gene under salt stress under the concentrations and time points analyzed. Pj Rab7 transgenic tobacco lines survived better under conditions of 150 mM NaCl stress compared to control un-transformed plants. Pj Rab7 transgenic plants were found to accumulate more sodium than control plants during salt stress. The results of our studies could be used as a starting point for generation of crop plants tolerant to abiotic stress.

Anti-apoptosis and cell survival: a review

Type I programmed cell death (PCD) or apoptosis is critical for cellular self-destruction for a variety of processes such as development or the prevention of oncogenic transformation. Alternative forms, including type II (autophagy) and type III (necrotic) represent the other major types of PCD that also serve to trigger cell death. PCD must be tightly controlled since disregulated cell death is involved in the development of a large number of different pathologies. To counter the multitude of processes that are capable of triggering death, cells have devised a large number of cellular processes that serve to prevent inappropriate or premature PCD. These cell survival strategies involve a myriad of coordinated and systematic physiological and genetic changes that serve to ward off death. Here we will discuss the different strategies that are used to prevent cell death and focus on illustrating that although anti-apoptosis and cellular survival serve to counteract PCD, they are nevertheless mechanistically distinct from the processes that regulate cell death.

Identification of the essential Brucella melitensis porin Omp2b as a suppressor of Bax-induced cell death in yeast in a genome-wide screening

Background

Inhibition of apoptosis is one of the mechanisms selected by numerous intracellular pathogenic bacteria to control their host cell. Brucellae, which are the causative agent of a worldwide zoonosis, prevent apoptosis of infected cells, probably to support survival of their replication niche.

Methodology/Principal Findings

In order to identify Brucella melitensis anti-apoptotic effector candidates, we performed a genome-wide functional screening in yeast. The B. melitensis ORFeome was screened to identify inhibitors of Bax-induced cell death in S. cerevisiae. B. melitensis porin Omp2b, here shown to be essential, prevents Bax lethal effect in yeast, unlike its close paralog Omp2a. Our results based on Omp2b size variants characterization suggest that signal peptide processing is required for Omp2b effect in yeast.

Conclusion/Significance

We report here the first application to a bacterial genome-wide library of coding sequences of this “yeast-rescue” screening strategy, previously used to highlight several new apoptosis regulators. Our work provides B. melitensis proteins that are candidates for an anti-apoptotic function, and can be tested in mammalian cells in the future. Hypotheses on possible molecular mechanisms of Bax inhibition by the B. melitensis porin Omp2b are discussed.

Reduced expression of the v-SNAREs AtVAMP71/AtVAMP7C gene family in Arabidopsis reduces drought tolerance by suppression of abscisic acid-dependent stomatal closure

Stomatal closure during water stress is a major plant mechanism for reducing the loss of water through leaves. The opening and closure of stomata are mediated by endomembrane trafficking. The role of the vacuolar trafficking pathway, that involves v-SNAREs of the AtVAMP71 family (formerly called AtVAMP7C) in stomatal movements, was analysed. Expression of AtVAMP711-14 genes was manipulated in Arabidopsis plants with sense or antisense constructs by transformation of the AtVAMP711 gene. Antisense plants exhibited decreased stomatal closure during drought or after treatment with abscisic acid (ABA), resulting in the rapid loss of leaf water and tissue collapse. No improvement was seen in plants overexpressing the AtVAMP711 gene, suggesting that wild-type levels of AtVAMP711 expression are sufficient. ABA treatment induced the production of reactive oxygen species (ROS) in guard cells of both wild-type and antisense plants, indicating that correct hormone sensing is maintained. ROS were detected in nuclei, chloroplasts, and vacuoles. ABA treatment caused a significant increase in ROS-containing small vacuoles and also in plastids and nuclei of neighbouring epidermal and mesophyll cells. Taken together, our results show that VAMP71 proteins play an important role in the localization of ROS, and in the regulation of stomatal closure by ABA treatment. The paper also describes a novel aspect of ROS signalling in plants: that of ROS production in small vacuoles that are dispersed in the cytoplasm.

Identification of ADP-ribosylation factor 4 as a suppressor of N-(4-hydroxyphenyl)retinamide-induced cell death

Yeast-based functional screening for inhibitors of Bcl-2-associated X protein (Bax)-induced cell death in yeast identified ADP-ribosylation factor 4 (ARF4) as a novel anti-apoptotic gene in human glioblastoma-derived U373MG cells. Yeast or U373MG cells that overexpressed ARF4 exhibited reduced reactive oxygen species (ROS) generation in response to Bax or N-(4-hydroxyphenyl)retinamide (4-HPR), respectively, which suggests that ROS play a role in the inhibition of cell death by ARF4. The 4-HPR-mediated phosphorylation of c-JUN N-terminal kinase, p38, and extracellular signal-regulated kinase was markedly suppressed in U373MG cells that stably expressed ARF4. Stable ARF4 transfectants were also refractory to 4-HPR-induced mitochondrial translocation of Bax, release of mitochondrial cytochrome c, and activation of caspase-3. Our results suggest that ARF4 participates in the regulation of glioblastoma apoptosis through the inhibition of stress-mediated apoptotic signals.

Cloning and characterization of three genes encoding Qb-SNARE proteins in rice

Qb-SNARE proteins belong to the superfamily of SNAREs (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) and function as important components of the vesicle trafficking machinery in eukaryotic cells. Here, we report three novel plant SNARE (NPSN) genes isolated from rice and named OsNPSN11, OsNPSN12 and OsNPSN13. They have about 70% nucleotide identity over their entire coding regions and similar genomic organization with ten exons and nine introns in each gene. Multiple alignment of deduced amino acid sequences indicate that the OsNPSNs proteins are homologous to AtNPSNs from Arabidopsis, containing a Qb-SNARE domain and a membrane-spanning domain in the C-terminal region. Semi-quantitative RT-PCR assays showed that the OsNPSNs were ubiquitously and differentially expressed in roots, culms, leaves, immature spikes and flowering spikes. The expression of OsNPSNs was significantly activated in rice seedlings treated with H(2)O(2), but down-regulated under NaCl and PEG6000 stresses. Transient expression method in onion epidermal cells revealed that OsNPSNs were located in the plasma membrane. Transformed yeast cells with OsNPSNs had better growth rates than empty-vector transformants when cultured on either solid or liquid selective media containing various concentrations of H(2)O(2), but more sensitive to NaCl and mannitol stresses. The 35S:OsNPSN11 transgenic tobacco also showed more tolerance to H(2)O(2) and sensitivity to NaCl and mannitol than non-transgenic tobacco. These results indicate that OsNPSNs may be involved in different aspects of the signal transduction in plant and yeast responses to abiotic stresses.

Integration of Arabidopsis thaliana stress-related transcript profiles, promoter structures, and cell-specific expression

The integration of stress-dependent, tissue- and cell-specific expression profiles and 5'-regulatory sequence motif analysis defines a common stress transcriptome, identifies major motifs for stress response, and places stress response in the context of tissue and cell lineages in the Arabidopsis root.

Background

Arabidopsis thaliana transcript profiles indicate effects of abiotic and biotic stresses and tissue-specific and cell-specific gene expression. Organizing these datasets could reveal the structure and mechanisms of responses and crosstalk between pathways, and in which cells the plants perceive, signal, respond to, and integrate environmental inputs.

Results

We clustered Arabidopsis transcript profiles for various treatments, including abiotic, biotic, and chemical stresses. Ubiquitous stress responses in Arabidopsis, similar to those of fungi and animals, employ genes in pathways related to mitogen-activated protein kinases, Snf1-related kinases, vesicle transport, mitochondrial functions, and the transcription machinery. Induced responses to stresses are attributed to genes whose promoters are characterized by a small number of regulatory motifs, although secondary motifs were also apparent. Most genes that are downregulated by stresses exhibited distinct tissue-specific expression patterns and appear to be under developmental regulation. The abscisic acid-dependent transcriptome is delineated in the cluster structure, whereas functions that are dependent on reactive oxygen species are widely distributed, indicating that evolutionary pressures confer distinct responses to different stresses in time and space. Cell lineages in roots express stress-responsive genes at different levels. Intersections of stress-responsive and cell-specific profiles identified cell lineages affected by abiotic stress.

Conclusion

By analyzing the stress-dependent expression profile, we define a common stress transcriptome that apparently represents universal cell-level stress responses. Combining stress-dependent and tissue-specific and cell-specific expression profiles, and Arabidopsis 5'-regulatory DNA sequences, we confirm known stress-related 5' cis-elements on a genome-wide scale, identify secondary motifs, and place the stress response within the context of tissues and cell lineages in the Arabidopsis root.

SNARE-Ware: The Role of SNARE-Domain Proteins in Plant Biology

In yeast and animal cells, members of the superfamily of N-ethylmaleimide-sensitive factor adaptor protein receptor (SNARE)-domain-containing proteins are key players in vesicle-associated membrane fusion events during transport processes between individual compartments of the endomembrane system, including exocytosis and endocytosis. Compared with genomes of other eukaryotes, genomes of monocotyledonous and dicotyledonous plants encode a surprisingly high number of SNARE proteins, suggesting vital roles for this protein class in higher plant species. Although to date it remains elusive whether plant SNARE proteins function like their yeast and animal counterparts, genetic screens have recently begun to unravel the variety of biological tasks in which plant SNAREs are involved. These duties involve fundamental processes such as cytokinesis, shoot gravitropism, pathogen defense, symbiosis, and abiotic stress responses, suggesting that SNAREs contribute essentially to many facets of plant biology.

Mitochondria-independent morphological and biochemical apoptotic alterations promoted by the anti-tumor agent bleomycin in Saccharomyces cerevisiae

Bleomycin is a highly potent cytotoxic and genotoxic agent used in the chemotherapy of various types of tumors. It is a radiomimetic anticancer drug that produces single- and double-stranded DNA breaks in a catalytic way. Using Saccharomyces cerevisiae as a model system, we show that when a high amount of bleomycin molecules is internalized (100 micromol/L), morphological changes identical to those usually associated with apoptosis, i.e., a sub-G1 region peak, chromatin condensation, and very rapid DNA fragmentation into oligonucleosomal-sized fragments, are observed. The known bleomycin inhibitors cobalt and EDTA were able to prevent bleomycin nucleasic activity and thus apoptotic cell death. However, both oligomycin, a potent inhibitor of the mitochondrial F0F1-ATPase, and antimycin, a drug affecting mitochondria respiration, were unable to prevent the bleomycin-induced apoptotic-like cell death. These results suggest that high bleomycin concentrations induce an apoptosis-like mitochondria-independent cell death in yeast.

The Arabidopsis BAP1 and BAP2 genes are general inhibitors of programmed cell death

Here we identify the BAP1 and BAP2 genes of Arabidopsis (Arabidopsis thaliana) as general inhibitors of programmed cell death (PCD) across the kingdoms. These two homologous genes encode small proteins containing a calcium-dependent phospholipid-binding C2 domain. BAP1 and its functional partner BON1 have been shown to negatively regulate defense responses and a disease resistance gene SNC1. Genetic studies here reveal an overlapping function of the BAP1 and BAP2 genes in cell death control. The loss of BAP2 function induces accelerated hypersensitive responses but does not compromise plant growth or confer enhanced resistance to virulent bacterial or oomycete pathogens. The loss of both BAP1 and BAP2 confers seedling lethality mediated by PAD4 and EDS1, two regulators of cell death and defense responses. Overexpression of BAP1 or BAP2 with their partner BON1 inhibits PCD induced by pathogens, the proapoptotic gene BAX, and superoxide-generating paraquat in Arabidopsis or Nicotiana benthamiana. Moreover, expressing BAP1 or BAP2 in yeast (Saccharomyces cerevisiae) alleviates cell death induced by hydrogen peroxide. Thus, the BAP genes function as general negative regulators of PCD induced by biotic and abiotic stimuli including reactive oxygen species. The dual roles of BAP and BON genes in repressing defense responses mediated by disease resistance genes and in inhibiting general PCD has implications in understanding the evolution of plant innate immunity.

Intracellular ROS: What Does it Do There?

Intracellular localization of stress induced reactive oxygen species (ROS) has emerged as an important aspect towards understanding of cellular responses to environmental stimuli. Our recent study published in the PNAS (103:18008-13)1 shows that NaCl-induced ROS appear within endosomes on the way to tonoplast as part of the vacuolar vesicle trafficking. In addition to showing ROS damage to the tonoplast, this finding may shed light upon recently reported aspects of root water relations during salt stress, suggesting a new signaling role for intracellular ROS in Arabidopsis root cells, during salt stress: ROS that are compartmentalized in endosomes are delivered by the vacuolar vesicle trafficking pathway to the tonoplast, resulting in oxidative gating of TIPs water channels. The closure of the tonoplast aquaporins contributes to the observed reduction in root hydraulic conductivity during salt stress.

Characterization of a novel alternatively spliced human transcript encoding an N-terminally truncated Vps24 protein that suppresses the effects of Bax in an ESCRT independent manner in yeast

Elucidating novel anti-apoptotic regulatory pathways is central to further understanding the molecular basis of several pathologies, including cancer. We have previously reported the identification of several mammalian cDNAs effective in preventing the lethal effects of heterologous expression of a pro-apoptotic BAX cDNA in yeast [Yang, Z., Khoury, C., Jean-Baptiste, G., Greenwood, M.T., 2006. Identification of mouse sphingomyelin synthase 1 (SMS1) as a suppressor of Bax mediated cell death in yeast. FEMS Yeast Res. 6, 751-762]. Here we report that one of the Bax suppressors encodes a novel 156 amino acid variant of the human Vps24 protein, Vps24beta, that lacks the N-terminal lipid binding domain of the well characterized 222 residue Vps24 (Vps24alpha). We demonstrate that the VPS24beta cDNA represents an expressed transcript that is likely produced by alternative splicing of the human VPS24 gene. Vps24alpha, but not Vps24beta, prevented the temperature and salt sensitive growth defects observed in a yeast mutant lacking a functional VPS24 gene. In contrast, Vps24beta, but not Vps24alpha, suppressed the inhibitory effects of Bax on yeast growth. Vps24beta protein also suppressed the effects of Bax in mutants lacking other VPS genes suggesting that a functional ESCRT pathway, of which the yeast Vps24p is an essential component, is not required for Vps24beta function. Taken together, we demonstrate that the human VPS24 gene gives rise to two functionally distinct proteins, one of which is involved in the ESCRT pathway and another novel protein that serves an anti-apoptotic role.

The mitochondrial pathway in yeast apoptosis

Mitochondria are not only important for the energetic status of the cell, but are also the fatal organelles deciding about cellular life and death. Complex mitochondrial features decisive for cell death execution in mammals are present and functional in yeast: AIF and cytochrome c release to the cytosol, mitochondrial fragmentation as well as mitochondrial hyperpolarisation followed by an oxidative burst, and breakdown of mitochondrial membrane potential. The easy accessibility of mitochondrial manipulations such as repression of respiration by growing yeast on glucose or deletion of mitochondrial DNA (rho(0)) on the one hand and the unique ability of yeast cells to grow on non-fermentable carbon sources by switching on mitochondrial respiration on the other hand have made yeast an excellent tool to delineate the necessity for mitochondria in cell death execution. Yeast research indicates that the connection between mitochondria and apoptosis is intricate, as abrogation of mitochondrial function can be either deleterious or beneficial for the cell depending on the specific context of the death scenario. Surprisingly, mitochondrion dependent yeast apoptosis currently helps to understand the aetiology (or the complex biology) of lethal cytoskeletal alterations, ageing and neurodegeneration. For example, mutation of mitochondrial superoxide dismutase or CDC48/VCP mutations, both implicated in several neurodegenerative disorders, are associated with mitochondrial impairment and apoptosis in yeast.

Vesicle trafficking in plant immune responses

In plants, perception of pathogen-associated molecular patterns at the surface is the first line of defence in cellular immunity. This review summarizes recent evidence of the involvement of vesicle trafficking in the plant's immune response against pathogens. I first discuss aspects of ligand-stimulated receptor endocytosis. The best-characterized pattern-recognition receptor (PRR), FLS2, is a transmembrane leucine-rich repeat receptor kinase that recognizes bacterial flagellin. FLS2 was recently shown to undergo internalization upon activation with its cognate ligand. An animal PRR, TLR4 that mediates perception of bacterial-derived lipopolysaccharides, similarly exhibits ligand-stimulated endocytosis. The second focus is N-ethylmaleimide-sensitive factor adaptor protein receptor (SNARE)-mediated immunity involving syntaxins and their cognate partners. One of the genes involved in basal immunity in Arabidopsis, PEN1, encodes a syntaxin that focally accumulates at fungal penetration sites, raising the possibility that induced exocytosis is important for active defence. Pathogen-triggered endocytic and exocytic processes have to be balanced to ensure host cell homeostasis. Thus, understanding how phytopathogens have evolved strategies to exploit host cell vesicle trafficking to manipulate immune responses is currently an area of intense study.

Suppression of Arabidopsis vesicle-SNARE expression inhibited fusion of H2O2-containing vesicles with tonoplast and increased salt tolerance

Intracellular vesicle trafficking performs essential functions in eukaryotic cells, such as membrane trafficking and delivery of molecules to their destinations. A major endocytotic route in plants is vesicle trafficking to the vacuole that plays an important role in plant salt tolerance. The final step in this pathway is mediated by the AtVAMP7C family of vesicle soluble N-ethylmaleimide-sensitive factor attachment protein receptors (v-SNAREs) that carry out the vesicle fusion with the tonoplast. Exposure to high-salt conditions causes immediate ionic and osmotic stresses, followed by production of reactive oxygen species. Here, we show that the reactive oxygen species are produced intracellularly, in endosomes that were targeted to the central vacuole. Suppression of the AtVAMP7C genes expression by antisense AtVAMP711 gene or in mutants of this family inhibited fusion of H2O2-containing vesicles with the tonoplast, which resulted in formation of H2O2-containing megavesicles that remained in the cytoplasm. The antisense and mutant plants exhibited improved vacuolar functions, such as maintenance of DeltapH, reduced release of calcium from the vacuole, and greatly improved plant salt tolerance. The antisense plants exhibited increased calcium-dependent protein kinase activity upon salt stress. Improved vacuolar ATPase activity during oxidative stress also was observed in a yeast system, in a DeltaVamp7 knockout strain. Interestingly, a microarray-based analysis of the AtVAMP7C genes showed a strong down-regulation of most genes in wild-type roots during salt stress, suggesting an evolutionary molecular adaptation of the vacuolar trafficking.

Mutation in a homolog of yeast Vps53p accounts for the heat and osmotic hypersensitive phenotypes in Arabidopsis hit1-1 mutant

Previously, the growth of Arabidopsis hit1-1 (heat-intolerant) mutant was found to be inhibited by both heat and water stress (Wu et al. in J Plant Physiol 157:543-547, 2000). In order to determine the genetic mutation underlying the hit1-1 phenotype, map-based cloning of HIT1 gene was conducted. Transformation of the hit1-1 mutant with a HIT1 cDNA clone reverts the mutant to the heat tolerance phenotype, confirming the identity of HIT1. Sequence analysis revealed the HIT1 gene encodes a protein of 829 amino acid residues and is homologous to yeast (Saccharomyces cerevisiae) Vps53p protein. The yeast Vps53p protein has been shown to be a tethering factor that associates with Vps52p and Vps54p in a complex formation involved in the retrograde trafficking of vesicles to the late Golgi. An Arabidopsis homolog of yeast Vps52p has previously been identified and mutation of either the homolog or HIT1 by T-DNA insertion resulted in a male-specific transmission defect. The growth of yeast vps53Delta null mutant also shows reduced thermotolerance, and expression of HIT1 in this mutant can partially complement the defect, supporting the possibility of a conserved biological function for Vps53p and HIT1. Collectively, the hit1-1 is the first mutant in higher plant linking a homolog of the vesicle tethering factor to both heat and osmotic stress tolerance.

Multivesicular compartments proliferate in susceptible and resistant MLA12-barley leaves in response to infection by the biotrophic powdery mildew fungus

There is growing evidence that multivesicular bodies and cell wall-associated paramural bodies participate in the enhanced vesicle trafficking induced by pathogen attack. Here, we performed transmission electron microscopy in combination with cytochemical localization of H2O2 to investigate multivesicular compartments during establishment of compatible interaction in susceptible barley (Hordeum vulgare) and during hypersensitive response in resistant MLA12-barley infected by the barley powdery mildew fungus (Blumeria graminis f. sp. hordei). Multivesicular bodies, intravacuolar vesicle aggregates and paramural bodies proliferated in the penetrated epidermal cell during development of the fungal haustorium. These vesicular structures also proliferated at the periphery of intact cells, which were adjacent to the hypersensitive dying cells and deposited cell wall appositions associated with H2O2 accumulation. All plasmodesmata between intact cells and hypersensitive cells were constricted or blocked by cell wall appositions. These results suggest that multivesicular compartments participate in secretion of building blocks for cell wall appositions not only to arrest fungal penetration but also to contain hypersensitive cell death through blocking plasmodesmata. They may also participate in internalization of damaged membranes, deleterious materials, nutrients, elicitors and elicitor receptors.

Old yellow enzyme interferes with Bax-induced NADPH loss and lipid peroxidation in yeast

The yeast transcriptional response to murine Bax expression was compared with the changes induced by H(2)O(2) treatment via microarray technology. Although most of the Bax-responsive genes were also triggered by H(2)O(2) treatment, OYE3, ICY2, MLS1 and BTN2 were validated to have a Bax-specific transcriptional response not shared with the oxidative stress trigger. In knockout experiments, only deletion of OYE3, coding for yeast Old yellow enzyme, attenuated the rate of Bax-induced growth arrest, cell death and NADPH decrease. Lipid peroxidation was completely absent in DeltaOYE3 expressing Bax. However, the absence of OYE3 sensitized yeast cells to H(2)O(2)-induced cell death, and increased the rate of NADPH decrease and lipid peroxidation. Our results clearly indicate that OYE3 interferes with Bax- and H(2)O(2)-induced lipid peroxidation and cell death in Saccharomyces cerevisiae.

A Novel Arabidopsis Gene Causes Bax-like Lethality in Saccharomyces cerevisiae

Overexpression of the mammalian proapoptotic protein Bax induces cell death in plant and yeast cells. The Bax inihibitor-1 (BI-1) gene rescues yeast and plant from Bax-mediated lethality. Using the Arabidopsis BI-1 (AtBI-1) gene controlled by the GAL1 promoter as a cell death suppressor in yeast, Cdf1 (cell growth defect factor-1) was isolated from Arabidopsis cDNA library. Overexpression of Cdf1 caused cell death in yeast, whereas such an effect was suppressed by co-expression of AtBI-1. The Cdf1 protein fused with a green fluorescent protein was localized in the mitochondria and resulted in the loss of mitochondrial membrane potential in yeast. The Bax-resistant mutant BRM1 demonstrated tolerance against Cdf1-mediated lethality, whereas the Deltaatp4 strain was sensitive to Cdf1. Our results suggest that Cdf1 and Bax cause mitochondria-mediated yeast lethality through partially overlapped pathways.

Mammalian Bax initiates plant cell death through organelle destruction

Mammalian Bax is known to cause cell death when expressed in plants. We examined transgenic plants expressing both Bax and organelle-targeted green fluorescent protein to determine the cellular changes that occur during Bax-induced cell death. The mitochondria changed morphologically from being bacilli-shaped to being round, eventually becoming swollen. Mitochondria streaming also stopped. The chloroplasts lost membrane function and their contents leaked out, followed by the disruption of the vacuole. Light was not essential for Bax-induced ion leakage or organelle disruption. These results indicate that Bax induces temporal and spatial cell death events at the organelle level in the plant. A heterologous system, using Bax, would therefore be available to investigate cell death, which is commonly conserved in animals and plants.

Valproic acid induces apoptosis dependent of Yca1p at concentrations that mildly affect the proliferation of yeast

Valproic acid (VPA) inhibited the growth of yeast in a dose-dependent manner with complete inhibition attained at 100 mM. When cells were exposed to 25 mM VPA, the wild-type died showing apoptotic markers, while yca1Delta deleted of YCA1 encoding yeast caspase 1 survived. On the other hand, when cells were exposed to 50 mM VPA, both the wild-type and yca1Delta died showing morphological features similar to those of the autophagic death of cdc28 which was also independent of YCA1. Thus, these results suggested that yeast cells die via YCA1-dependent apoptosis when their proliferative activity is mildly impaired.

Stress in recombinant protein producing yeasts

It is well established today that heterologous overexpression of proteins is connected with different stress reactions. The expression of a foreign protein at a high level may either directly limit other cellular processes by competing for their substrates, or indirectly interfere with metabolism, if their manufacture is blocked, thus inducing a stress reaction of the cell. Especially the unfolded protein response (UPR) in Saccharomyces cerevisiae (as well as some other yeasts) is well documented, and its role for the limitation of expression levels is discussed. One potential consequence of endoplasmatic reticulum folding limitations is the ER associated protein degradation (ERAD) involving retrotranslocation and decay in the cytosol. High cell density fermentation, the typical process design for recombinant yeasts, exerts growth conditions that deviate far from the natural environment of the cells. Thus, different environmental stresses may be exerted on the host. High osmolarity, low pH and low temperature are typical stress factors. Whereas the molecular pathways of stress responses are well characterized, there is a lack of knowledge concerning the impact of stress responses on industrial production processes. Accordingly, most metabolic engineering approaches conducted so far target at the improvement of protein folding and secretion, whereas only few examples of cell engineering against general stress sensitivity were published. Apart from discussing well-documented stress reactions of yeasts in the context of heterologous protein production, some more speculative topics like quorum sensing and apoptosis are addressed.

A Kluyveromyces lactis mutant in the essential gene KlLSM4 shows phenotypic markers of apoptosis

We report the study of Kluyveromyces lactis cells expressing a truncated form of KlLSM4, a gene ortholog to LSM4 of Saccharomyces cerevisiae which encodes an essential protein involved in both pre-mRNA splicing and mRNA decapping. We had previously demonstrated that the first 72 amino acids of the K. lactis Lsm4p (KlLsm4Deltap) can restore cell growth in both K. lactis and S. cerevisiae cells not expressing the endogenous protein. However, cells showed a remarkable loss of viability in stationary phase. Here we report that cells expressing KlLsm4Deltap presented clear apoptotic markers such as chromatin condensation, DNA fragmentation, accumulation of reactive oxygen species, and showed increased sensitivity to different drugs. RNA analysis revealed that pre-mRNA splicing was almost normal while mRNA degradation was significantly delayed, pointing to this as the possible step responsible for the observed phenotypes.

Sugar-induced apoptosis in yeast cells

Sugars induce death of Saccharomyces cerevisiae within a few hours in the absence of additional nutrients to support growth; by contrast, cells incubated in water or in the presence of other nutrients without sugar remain viable for weeks. Here we show that this sugar-induced cell death (SICD) is characterized by rapid production of reactive oxygen species (ROS), RNA and DNA degradation, membrane damage, nucleus fragmentation and cell shrinkage. Addition of ascorbic acid to sugar-incubated cells prevents SICD, indicating that SICD is initiated by ROS. The lack of a protection mechanism against SICD suggests that sugars use to be the limiting nutrients for yeast and are probably depleted before all other nutrients. Being the limiting nutrient, sugars became the growth-stimulating agent, signaling the presence of sufficient nutrients for growth, but in the absence of the complementing nutrients they induce apoptotic death.

Bax-induced cell death of Arabidopsis is meditated through reactive oxygen-dependent and -independent processes

An Arabidopsis protoplast system was developed for dissecting plant cell death in individual cells. Bax, a mammalian pro-apoptotic member of the Bcl-2 family, induces apoptotic-like cell death in Arabidopsis. Bax accumulation in Arabidopsis mesophyll protoplasts expressing murine Bax cDNA from a glucocorticoid-inducible promoter results in cytological characteristics of apoptosis, namely DNA fragmentation, increased vacuolation, and loss of plasma membrane integrity. In vivo targeting analysis monitored using jellyfish green fluorescent protein (GFP) reporter indicated full-length Bax was localized to the mitochondria, as it does in animal cells. Deletion of the carboxyl-terminal transmembrane domain of Bax completely abolished targeting to mitochondria. Bax expression was followed by reactive oxygen species (ROS) accumulation. Treatment of protoplasts with the antioxidant N -acetyl- -cysteine (NAC) during induction of Bax expression strongly suppressed Bax-mediated ROS production and the cell death phenotype. However, some population of the ROS depleted cells still induced cell death, indicating that there is a process that Bax-mediated plant cell death is independent of ROS accumulation. Accordingly, suppression of Bax-mediated plant cell death also takes place in two different processes. Over-expression of a key redox-regulator, Arabidopsis nucleoside diphosphate kinase 2 (AtNDPK2) down-regulated ROS accumulation and suppressed Bax-mediated cell death and transient expression of Arabidopsis Bax inhibitor-1 (AtBI-1) substantially suppressed Bax-induced cell death without altering cellular ROS level. Taken together, our results collectively suggest that the Bax-mediated cell death and its suppression in plants is mediated by ROS-dependent and -independent processes.

Induction of salt and osmotic stress tolerance by overexpression of an intracellular vesicle trafficking protein AtRab7 (AtRabG3e)

Adaptation to stress requires removal of existing molecules from various cellular compartments and replacing them with new ones. The transport of materials to and from the specific compartments involved in the recycling and deposition of macromolecules is carried out by an intracellular vesicle trafficking system. Here, we report the isolation of a vesicle trafficking-regulating gene, AtRabG3e (formerly AtRab7), from Arabidopsis. The gene was induced during programmed cell death after treatment of intact leaves with superoxide and salicylic acid or infection with necrogenic pathogens. Transgenic plants that expressed the AtRabG3e gene under the constitutive 35S promoter from cauliflower mosaic virus exhibited accelerated endocytosis in roots, leaves, and protoplasts. The transgenic plants accumulated sodium in the vacuoles and had higher amounts of sodium in the shoots. The transgenic plants also showed increased tolerance to salt and osmotic stresses and reduced accumulation of reactive oxygen species during salt stress. These results imply that vesicle trafficking plays an important role in plant adaptation to stress, beyond the housekeeping function in intracellular vesicle trafficking.

A comprehensive analysis of hydrogen peroxide-induced gene expression in tobacco

Hydrogen peroxide plays a central role in launching the defense response during stress in plants. To establish a molecular profile provoked by a sustained increase in hydrogen peroxide levels, catalase-deficient tobacco plants (CAT1AS) were exposed to high light (HL) intensities over a detailed time course. The expression kinetics of >14000 genes were monitored by using transcript profiling technology based on cDNA-amplified fragment length polymorphism. Clustering and sequence analysis of 713 differentially expressed transcript fragments revealed a transcriptional response that mimicked that reported during both biotic and abiotic stresses, including the up-regulation of genes involved in the hypersensitive response, vesicular transport, posttranscriptional processes, biosynthesis of ethylene and jasmonic acid, proteolysis, mitochondrial metabolism, and cell death, and was accompanied by a very rapid up-regulation of several signal transduction components. Expression profiling corroborated by functional experiments showed that HL induced photoinhibition in CAT1AS plants and that a short-term HL exposure of CAT1AS plants triggered an increased tolerance against a subsequent severe oxidative stress.

Bcl-2 family members inhibit oxidative stress-induced programmed cell death in Saccharomyces cerevisiae

Selected antiapoptotic genes were expressed in baker's yeast (Saccharomyces cerevisiae) to evaluate cytoprotective effects during oxidative stress. When exposed to treatments resulting in the generation of reactive oxygen species (ROS), including H(2)O(2), menadione, or heat shock, wild-type yeast died and exhibited apoptotic-like characteristics, consistent with previous studies. Yeast strains were generated expressing nematode ced-9, human bcl-2, or chicken bcl-xl genes. These transformants tolerated a range of oxidative stresses, did not display features associated with apoptosis, and remained viable under conditions that were lethal to wild-type yeast. Yeast strains expressing a mutant antiapoptotic gene (bcl-2 deltaalpha 5-6), known to be nonfunctional in mammalian cells, were unable to tolerate any of the ROS-generating insults. These data are the first report showing CED-9 has cytoprotective effects against oxidative stress, and add CED-9 to the list of Bcl-2 protein family members that modulate ROS-mediated programmed cell death. In addition, these data indicate that Bcl-2 family members protect wild-type yeast from physiological stresses. Taken together, these data support the concept of the broad evolutionary conservation and functional similarity of the apoptotic processes in eukaryotic organisms.

The expression of the t-SNARE AtSNAP33 is induced by pathogens and mechanical stimulation

The fusion of vesicles in the secretory pathway involves the interaction of t-soluble N-ethylmaleimide-sensitive factor attachment protein receptors (t-SNAREs) on the target membrane and v-SNAREs on the vesicle membrane. AtSNAP33 is an Arabidopsis homolog of the neuronal t-SNARE SNAP-25 involved in exocytosis and is localized at the cell plate and at the plasma membrane. In this paper, the expression of AtSNAP33 was analyzed after different biotic and abiotic stresses. The expression of AtSNAP33 increased after inoculation with the pathogens Plectosporium tabacinum and virulent and avirulent forms of Peronospora parasitica and Pseudomonas syringae pv tomato. The expression of PR1 transcripts encoding the secreted pathogenesis-related protein 1 also increased after inoculation with these pathogens and the expression of AtSNAP33 preceded or occurred at the same time as the expression of PR1. AtSNAP33 was also expressed in npr1 plants that do not express PR1 after pathogen inoculation as well as in cpr1 plants that overexpress PR1 in the absence of a pathogen. The level of AtSNAP33 decreased slightly in leaves inoculated with P. parasitica in the NahG plants, and eds5 and sid2 mutants that are unable to accumulate salicylic acid (SA) after pathogen inoculation, indicating a partial dependence on SA. AtSNAP33 was also expressed in systemic noninoculated leaves of plants inoculated with P. syringae. In contrast to the situation in infected leaves, the expression of AtSNAP33 in systemic leaves was fully SA dependent. Thus, the expression of AtSNAP33 after pathogen attack is regulated by SA-dependent and SA-independent pathways. Mechanical stimulation also led to an increase of AtSNAP33 transcripts.

A truncated form of KlLsm4p and the absence of factors involved in mRNA decapping trigger apoptosis in yeast

The LSM4 gene of Saccharomyces cerevisiae codes for an essential protein involved in pre-mRNA splicing and also in mRNA decapping, a crucial step for mRNA degradation. We previously demonstrated that the first 72 amino acids of the Kluyveromyces lactis Lsm4p (KlLsm4p), which contain the Sm-like domains, can restore cell viability in both K. lactis and S. cerevisiae cells not expressing the endogenous protein. However, the absence of the carboxy-terminal region resulted in a remarkable loss of viability in stationary phase cells (). Herein, we demonstrate that S. cerevisiae cells expressing the truncated LSM4 protein of K. lactis showed the phenotypic markers of yeast apoptosis such as chromatin condensation, DNA fragmentation, and accumulation of reactive oxygen species. The study of deletion mutants revealed that apoptotic markers were clearly evident also in strains lacking genes involved in mRNA decapping, such as LSM1, DCP1, and DCP2, whereas a slight effect was observed in strains lacking the genes DHH1 and PAT1. This is the first time that a connection between mRNA stability and apoptosis is reported in yeast, pointing to mRNA decapping as the crucial step responsible of the observed apoptotic phenotypes.