A homologue of the defender against the apoptotic death gene (dad1 )in UV-exposed Chlamydomonas cells is downregulated with the onset of programmed cell death

Evaluation of Shifts of Gene Transcription Levels of Unicellular Green Alga Chlamydomonas reinhardtii Due to UV-C Irradiation

Green algae produce valuable lipids as carbon-recycling resources. Collecting whole cells with the intracellular lipids could be efficient without cell burst; however, direct use of the cells causes microbial contamination in environments. Then, UV-C irradiation was selected to satisfy the requirements of avoiding the cell burst and sterilizing cells with Chlamydomonas reinhardtii. UV-C irradiation with 1.209 mW·cm−2 showed enough sterilization activity for 1.6 × 107 cells·mL−1 of C. reinhardtii in a depth of 5 mm for 10 min. The irradiation showed no effects to composition and contents of the intracellular lipids. From the viewpoint of transcriptomic analysis, the irradiation displayed possibilities of (i) inhibition of the synthesis of lipids due to decrement of the transcription of related genes, such as diacylglycerol acyl transferase and cyclopropane fatty acid synthase, and (ii) activation of lipid degradation and the production of NADH2+ and FADH2 due to increment of the transcription of related genes, such as isocitrate dehydrogenase, dihydrolipoamide dehydrogenase and malate dehydrogenase. Irradiation until cell death could be insufficient to shift the metabolic flows even though the transcriptions were already shifted to lipid degradation and energy production. This paper is the first report of the response of C. reinhardtii to UV-C irradiation on the transcription level.

The APAF1_C/WD40 repeat domain-encoding gene from the sea lettuce Ulva mutabilis sheds light on the evolution of NB-ARC domain-containing proteins in green plants

We advance Ulva's genetic tractability and highlight its value as a model organism by characterizing its APAF1_C/WD40 domain-encoding gene, which belongs to a family that bears homology to R genes. The multicellular chlorophyte alga Ulva mutabilis (Ulvophyceae, Ulvales) is native to coastal ecosystems worldwide and attracts both high socio-economic and scientific interest. To further understand the genetic mechanisms that guide its biology, we present a protocol, based on adapter ligation-mediated PCR, for retrieving flanking sequences in U. mutabilis vector-insertion mutants. In the created insertional library, we identified a null mutant with an insertion in an apoptotic protease activating factor 1 helical domain (APAF1_C)/WD40 repeat domain-encoding gene. Protein domain architecture analysis combined with phylogenetic analysis revealed that this gene is a member of a subfamily that arose early in the evolution of green plants (Viridiplantae) through the acquisition of a gene that also encoded N-terminal nucleotide-binding adaptor shared by APAF-1, certain R-gene products and CED-4 (NB-ARC) and winged helix-like (WH-like) DNA-binding domains. Although phenotypic analysis revealed no mutant phenotype, gene expression levels in control plants correlated to the presence of bacterial symbionts, which U. mutabilis requires for proper morphogenesis. In addition, our analysis led to the discovery of a putative Ulva nucleotide-binding site and leucine-rich repeat (NBS-LRR) Resistance protein (R-protein), and we discuss how the emergence of these R proteins in green plants may be linked to the evolution of the APAF1_C/WD40 protein subfamily.

Physiological, Transcriptomic Investigation on the Tea Plant Growth and Yield Motivation by Chitosan Oligosaccharides

Chitosan oligosaccharides (COS) has been abundantly studied for its application on regulating plant growth of many horticultural and agricultural crops. We presented here the effect of COS on tea plant growth and yield by physiological and transcriptomic checking. The results showed that COS treatment can enhance the antioxidant activity of superoxide dismutase (SOD) and peroxidase (POD) and increase the content of chlorophyll and soluble sugar in tea plants. The field trail results show that COS treatment can increase tea buds’ density by 13.81–23.16%, the weight of 100 buds by 15.94–18.15%, and the yield by 14.22–21.08%. Transcriptome analysis found 5409 COS-responsive differentially expressed genes (DEGs), including 3149 up-regulated and 2260 down-regulated genes, and concluded the possible metabolism pathway that responsible for COS promoting tea plant growth. Our results provided fundamental information for better understanding the molecular mechanisms for COS’s acting on tea plant growth and yield promotion and offer academic support for its practical application in tea plant.

Emerging role of BAD and DAD1 as potential targets and biomarkers in cancer

As key regulators of apoptosis, BAD and defender against apoptotic cell death 1 (DAD1) are associated with cancer initiation and progression. Multiple studies have demonstrated that BAD and DAD1 serve critical roles in several types of cancer and perform various functions, such as participating in cellular apoptosis, invasion and chemosensitivity, as well as their role in diagnostic/prognostic judgement, etc. Investigating the detailed mechanisms of the cancerous effects of the two proteins will contribute to enriching the options for targeted therapy, and may improve clinical treatment of cancer. The present review summarizes research advances regarding the associations of BAD and DAD1 with cancer, and a hypothesis on the feasible relationship and interaction mechanism between the two proteins is proposed. Furthermore, the present review highlights the potential of the two proteins as therapeutic targets and valuable diagnostic and prognostic biomarkers.

Structural characterization of a novel KH-domain containing plant chloroplast endonuclease

Chlamydomonas reinhardtii is a single celled alga that undergoes apoptosis in response to UV-C irradiation. UVI31+, a novel UV-inducible DNA endonuclease in C. reinhardtii, which normally localizes near cell wall and pyrenoid regions, gets redistributed into punctate foci within the whole chloroplast, away from the pyrenoid, upon UV-stress. Solution NMR structure of the first putative UV inducible endonuclease UVI31+ revealed an α₁–β₁–β₂–α₂–α₃–β₃ fold similar to BolA and type II KH-domain ubiquitous protein families. Three α−helices of UVI31+ constitute one side of the protein surface, which are packed to the other side, made of three-stranded β–sheet, with intervening hydrophobic residues. A twenty-three residues long polypeptide stretch (D54-H76) connecting β₁ and β₂ strands is found to be highly flexible. Interestingly, UVI31+ recognizes the DNA primarily through its β–sheet. We propose that the catalytic triad residues involving Ser114, His95 and Thr116 facilitate DNA endonuclease activity of UVI31+. Further, decreased endonuclease activity of the S114A mutant is consistent with the direct participation of Ser114 in the catalysis. This study provides the first structural description of a plant chloroplast endonuclease that is regulated by UV-stress response.

Ethylene modulates root cortical senescence in barley

Background and Aims

Root cortical senescence (RCS) is a poorly understood phenomenon with implications for adaptation to edaphic stress. It was hypothesized that RCS in barley (Hordeum vulgare L.) is (1) accelerated by exogenous ethylene exposure; (2) accompanied by differential expression of ethylene synthesis and signalling genes; and (3) associated with differential expression of programmed cell death (PCD) genes.

Methods

Gene expression of root segments from four barley genotypes with and without RCS was evaluated using quantitative real-time PCR (qRT-PCR). The progression of RCS was manipulated with root zone ethylene and ethylene inhibitor applications.

Key Results

The results demonstrate that ethylene modulates RCS. Four genes related to ethylene synthesis and signalling were upregulated during RCS in optimal, low nitrogen and low phosphorus nutrient regimes. RCS was accelerated by root zone ethylene treatment, and this effect was reversed by an ethylene action inhibitor. Roots treated with exogenous ethylene had 35 and 46 % more cortical senescence compared with the control aeration treatment in seminal and nodal roots, respectively. RCS was correlated with expression of two genes related to programmed cell death (PCD).

Conclusions

The development of RCS is similar to root cortical aerenchyma formation with respect to ethylene modulation of the PCD process.

Stress responses of the oil-producing green microalga Botryococcus braunii Race B

Plants react to biotic and abiotic stresses with a variety of responses including the production of reactive oxygen species (ROS), which may result in programmed cell death (PCD). The mechanisms underlying ROS production and PCD have not been well studied in microalgae. Here, we analyzed ROS accumulation, biomass accumulation, and hydrocarbon production in the colony-forming green microalga Botryococcus braunii in response to several stress inducers such as NaCl, NaHCO₃, salicylic acid (SA), methyl jasmonate, and acetic acid. We also identified and cloned a single cDNA for the B. braunii ortholog of the Arabidopsis gene defender against cell death 1 (DAD1), a gene that is directly involved in PCD regulation. The function of B. braunii DAD1 was assessed by a complementation assay of the yeast knockout line of the DAD1 ortholog, oligosaccharyl transferase 2. Additionally, we found that DAD1 transcription was induced in response to SA at short times. These results suggest that B. braunii responds to stresses by mechanisms similar to those in land plants and other  organisms.

¹H, ¹³C and ¹⁵N NMR assignments of a mutant of UV inducible transcript (S55A-UVI31+) from Chlamydomonas reinhardtii

Almost complete sequence specific (1)H, (13)C and (15)N resonance assignments of a mutant of UV inducible transcript (S55A-UVI31+) from Chlamydomonas reinhardtii are reported, as a prelude to its structural and functional characterization. Site-directed mutagenesis of uvi31+ was carried out using complementary mutation harbouring oligonucleotides for S55A mutant. The resulting mutant was sequenced and then S55A mutant of uvi31+ cDNA were expressed in E. coli, and purification were carried out from where the protein was purified to high homogeneity. The point mutation S55A in UVI31+ results in a significant enhancement in its DNA endonuclease activity as compared to its wild type protein.

Oxidative stress contributes to autophagy induction in response to endoplasmic reticulum stress in Chlamydomonas reinhardtii

The accumulation of unfolded/misfolded proteins in the endoplasmic reticulum (ER) results in the activation of stress responses, such as the unfolded protein response or the catabolic process of autophagy to ultimately recover cellular homeostasis. ER stress also promotes the production of reactive oxygen species, which play an important role in autophagy regulation. However, it remains unknown whether reactive oxygen species are involved in ER stress-induced autophagy. In this study, we provide evidence connecting redox imbalance caused by ER stress and autophagy activation in the model unicellular green alga Chlamydomonas reinhardtii. Treatment of C. reinhardtii cells with the ER stressors tunicamycin or dithiothreitol resulted in up-regulation of the expression of genes encoding ER resident endoplasmic reticulum oxidoreductin1 oxidoreductase and protein disulfide isomerases. ER stress also triggered autophagy in C. reinhardtii based on the protein abundance, lipidation, cellular distribution, and mRNA levels of the autophagy marker ATG8. Moreover, increases in the oxidation of the glutathione pool and the expression of oxidative stress-related genes were detected in tunicamycin-treated cells. Our results revealed that the antioxidant glutathione partially suppressed ER stress-induced autophagy and decreased the toxicity of tunicamycin, suggesting that oxidative stress participates in the control of autophagy in response to ER stress in C. reinhardtii In close agreement, we also found that autophagy activation by tunicamycin was more pronounced in the C. reinhardtii sor1 mutant, which shows increased expression of oxidative stress-related genes.

Menadione-induced caspase-dependent programmed cell death in the green chlorophyte Chlamydomonas reinhardtii

Menadione, a quinone that undergoes redox cycles leading to the formation of superoxide radicals, induces programmed cell death (PCD) in animals and plants. In this study, we investigated whether the unicellular green alga Chlamydomonas reinhardtii P.A.Dangeard is capable of executing PCD upon exposure to menadione stress. We report here, the morphological, molecular, and biochemical changes after menadione exposure of C. reinhardtii cells. The effect of menadione on cell death has been shown to be dose-dependent; 5-100 μM menadione causes 20%-46% cell death, respectively. It appears that growth is inhibited with the concomitant degradation of the photosynthetic pigments and by a decrease in the photosynthetic capacity. Being an oxidative stress, we found an H2 O2 burst within 15 min of menadione exposure, followed by an increase in antioxidant enzyme (superoxide dismutase [SOD], catalase [CAT], and ascorbate peroxidase [APX]) activities. In parallel, RT-PCR was performed for transcript analyses of Mn-SOD, CAT, and APX. Our results clearly revealed that expression of these genes were up-regulated upon menadione exposure. Furthermore, classical hallmarks of PCD such as alteration of mitochondrial membrane potential, significant increase in caspase-3-like DEVDase activity, cleavage of poly (ADP) ribose polymerase (PARP)-1-like enzyme, and DNA fragmentation as detected by terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) assay and oligosomal DNA fragmentation were observed. Moreover, antibodies against a mammalian active caspase-3 shared epitopes with a caspase-3-like protein of ~17 kDa; its pattern of expression and activity correlated with the onset of cell death. To the best of our knowledge, this is the first report on menadione-induced PCD through a mitochondrian-caspase protease pathway in an algal species.

Dehydroascorbate: a possible surveillance molecule of oxidative stress and programmed cell death in the green alga Chlamydomonas reinhardtii

Chlamydomonas reinhardtii tolerates relatively high H2 O2 levels that induce an array of antioxidant activities. However, rather than rendering the cells more resistant to oxidative stress, the cells become far more sensitive to an additional H2 O2 dose. If H2 O2 is provided 1.5-9 h after an initial dose, it induces programmed cell death (PCD) in the wild-type, but not in the dum1 mutant impaired in the mitochondrial respiratory complex III. This mutant does not exhibit a secondary oxidative burst 4-5 h after the inducing H2 O2 , nor does it activate metacaspase-1 after the second H2 O2 treatment. The intracellular dehydroascorbate level, a product of ascorbate peroxidase, increases under conditions leading to PCD. The addition of dehydroascorbate induces PCD in the wild-type and dum1 cultures, but higher levels are required in dum1 cells, where it is metabolized faster. The application of dehydroascorbate induces the expression of metacaspase-2, which is much stronger than the expression of metacaspase-1. The presence or absence of oxidative stress, in addition to the rise in internal dehydroascorbate, may determine which metacaspase is activated during Chlamydomonas PCD. Cell death is strongly affected by the timing of H2 O2 or dehydroascorbate admission to synchronously grown cultures, suggesting that the cell cycle phase may distinguish cells that perish from those that do not.

¹H, ¹³C and ¹⁵N resonance assignments of S114A mutant of UVI31+ from Chlamydomonas reinhardtii

Almost complete sequence specific (1)H, (13)C and (15)N resonance assignments of S114A mutant of UVI31+ from Chlamydomonas reinhardtii are reported. The cDNA of S114A mutant of UVI31+ was cloned from a eukaryotic green algae (C. reinhardtii) and overexpressed in E.coli from where the protein was purified to homogeneity. The point mutation S114A in UVI31+ reduces its DNA endonuclease activity substantially as compared with its wild type. As a prelude to the structural characterization of S114A mutant of UVI31+, we report here complete sequence-specific (1)H, (13)C and (15)N NMR assignments.

Two calcium-dependent protein kinases from Chlamydomonas reinhardtii are transcriptionally regulated by nutrient starvation

We report here, the transcriptional regulation of 2 Calcium Dependent Protein Kinases in response to nutrient starvation of Chlamydomonas reinhardtii vegetative cells. The CDPK proteins, CDPK1 and CDPK3; share 53% identity among themselves, a maximum of 57% and 52% to higher plants respectively and 42% to apicomplexan protozoans. We expressed a CDPK1-GFP fusion protein in the C. reinhardtii vegetative cells and showed its distribution both in the cell body and the membrane-matrix fraction of the flagella. The fusion protein exhibits mobility shift in the presence of Ca (2+), confirming its Ca (2+)-binding properties. To the best of our knowledge, this is the first report of transcriptional regulation of CDPKs from a unicellular chlorophyte in response to nutrient starvation namely acetate (A), phosphorus (P), and nitrogen (N).

Apoptosis-like cell death pathways in the unicellular parasite Toxoplasma gondii following treatment with apoptosis inducers and chemotherapeutic agents: a proof-of-concept study

Ancient pathways of an apoptosis-like cell death have been identified in unicellular eukaryotes including protozoan parasites. Here, we examined programmed cell death in the apicomplexan Toxoplasma gondii which is a common intracellular pathogen of humans and warm-blooded animals. Treatment of extracellular T. gondii with various pro-apoptotic stimuli significantly induced DNA strand breaks as revealed by TUNEL and flow cytometry. Using staurosporine or miltefosine as pro-apoptotic stimuli, parasites also presented a reduced cell size, i.e. pyknosis and externalized phosphatidylserine while the plasma membrane remained intact. Importantly, staurosporine also induced DNA strand breaks in intracellular T. gondii. Data mining of the Toxoplasma genome resource identified 17 putative cell death-associated genes encoding proteases, a nuclease and several apoptosis regulators. Staurosporine-treated parasites but not controls strongly up-regulated several of these genes in a time-dependent fashion with a putative PDCD2 protein being more than 100-fold up-regulated. However, the mitochondrial membrane potential (ΔΨ_m) remained intact and caspase-like activity increased only slightly during staurosporine-triggered cell death. As compared to staurosporine, the transcriptional response of parasites to miltefosine was more restricted but PDCD2 was again strongly induced. Furthermore, T. gondii lost their ΔΨ_m and rapidly presented strong caspase-like activity during miltefosine treatment. Consequently, protease inhibitors abrogated miltefosine-induced but not staurosporine-induced Toxoplasma cell death. Finally, toxoplasmacidal drugs triggered DNA strand breaks in extracellular T. gondii. Interestingly, clindamycin also induced markers of an apoptosis-like cell death in intracellular parasites. Together, the data indicate that T. gondii possesses ancient apoptosis-like cell death machinery which can be triggered by chemotherapeutic agents.

New insights into Chlamydomonas reinhardtii hydrogen production processes by combined microarray/RNA-seq transcriptomics

Hydrogen production with Chlamydomonas reinhardtii induced by sulphur starvation is a multiphase process while the cell internal metabolism is completely remodelled. The first cellular response is characterized by induction of genes with regulatory functions, followed by a total remodelling of the metabolism to provide reduction equivalents for cellular processes. We were able to characterize all major processes that provide energy and reduction equivalents during hydrogen production. Furthermore, C. reinhardtii showed a strong transcript increase for gene models responsible for stress response and detoxification of oxygen radicals. Finally, we were able to determine potential bottlenecks and target genes for manipulation to increase hydrogen production or to prolong the hydrogen production phase. The investigation of transcriptomic changes during the time course of hydrogen production in C. reinhardtii with microarrays and RNA-seq revealed new insights into the regulation and remodelling of the cell internal metabolism. Both methods showed a good correlation. The microarray platform can be used as a reliable standard tool for routine gene expression analysis. RNA-seq additionally allowed a detailed time-dependent study of gene expression and determination of new genes involved in the hydrogen production process.

Mastoparan-induced programmed cell death in the unicellular alga Chlamydomonas reinhardtii

BACKGROUND AND AIMS

Under stress-promoting conditions unicellular algae can undergo programmed cell death (PCD) but the mechanisms of algal cellular suicide are still poorly understood. In this work, the involvement of caspase-like proteases, DNA cleavage and the morphological occurrence of cell death in wasp venom mastoparan (MP)-treated Chlamydomonas reinhardtii were studied.

METHODS

Algal cells were exposed to MP and cell death was analysed over time. Specific caspase inhibitors were employed to elucidate the possible role of caspase-like proteases. YVADase activity (presumably a vacuolar processing enzyme) was assayed by using a fluorogenic caspase-1 substrate. DNA breakdown was evaluated by DNA laddering and Comet analysis. Cellular morphology was examined by confocal laser scanning microscopy.

KEY RESULTS

MP-treated C. reinhardtii cells expressed several features of necrosis (protoplast shrinkage) and vacuolar cell death (lytic vesicles, vacuolization, empty cell-walled corpse-containing remains of digested protoplast) sometimes within one single cell and in different individual cells. Nucleus compaction and DNA fragmentation were detected. YVADase activity was rapidly stimulated in response to MP but the early cell death was not inhibited by caspase inhibitors. At later time points, however, the caspase inhibitors were effective in cell-death suppression. Conditioned medium from MP-treated cells offered protection against MP-induced cell death.

CONCLUSIONS

In C. reinhardtii MP triggered PCD of atypical phenotype comprising features of vacuolar and necrotic cell deaths, reminiscent of the modality of hypersensitive response. It was assumed that depending on the physiological state and sensitivity of the cells to MP, the early cell-death phase might be not mediated by caspase-like enzymes, whereas later cell death may involve caspase-like-dependent proteolysis. The findings substantiate the hypothesis that, depending on the mode of induction and sensitivity of the cells, algal PCD may take different forms and proceed through different pathways.

A BolA-like morphogene from the alga Chlamydomonas reinhardtii changes morphology and induces biofilm formation in Escherichia coli

Escherichia coli BolA protein is a stress-inducible morphogene, regulates transcription, forms biofilms and interacts with monothiol glutaredoxins. Its presence has been documented in plants but its role remains enigmatic. This study attempts to functionally dissect the role of a BolA-domain-containing protein in the alga Chlamydomonas reinhardtii. Of the five C. reinhardtii bolA-like genes annotated for the presence of BolA-domain, the open reading frame with the highest similarity to algal systems was cloned and the protein over-expressed in E. coli. This over-expression did not affect E. coli growth but induced biofilm formation and changed its morphology, indicating functional conservancy. This is the first compelling evidence depicting the role of a plant BolA-like protein in morphogenetic pathway and biofilm formation. The implications of the phenotypic consequences of this heterologous expression are discussed.

UVI31+ is a DNA endonuclease that dynamically localizes to chloroplast pyrenoids in C. reinhardtii

UVI31+ is an evolutionarily conserved BolA family protein. In this study we examine the presence, localization and possible functions of this protein in the context of a unicellular alga, Chlamydomonas reinhardtii. UVI31+ in C. reinhardtii exhibits DNA endonuclease activity and is induced upon UV stress. Further, UVI31+ that normally localizes to the cell wall and pyrenoid regions gets redistributed into punctate foci within the whole chloroplast, away from the pyrenoid, upon UV stress. The observed induction upon UV-stress as well as the endonuclease activity suggests plausible role of this protein in DNA repair. We have also observed that UV31+ is induced in C. reinhardtii grown in dark conditions, whereby the protein localization is enhanced in the pyrenoid. Biomolecular interaction between the purified pyrenoids and UVI31+ studied by NMR demonstrates the involvement of the disordered loop domain of the protein in its interaction.

Expression and putative function of innate immunity genes under in situ conditions in the symbiotic hydrothermal vent tubeworm Ridgeia piscesae

The relationships between hydrothermal vent tubeworms and sulfide-oxidizing bacteria have served as model associations for understanding chemoautotrophy and endosymbiosis. Numerous studies have focused on the physiological and biochemical adaptations that enable these symbioses to sustain some of the highest recorded carbon fixation rates ever measured. However, far fewer studies have explored the molecular mechanisms underlying the regulation of host and symbiont interactions, specifically those mediated by the innate immune system of the host. To that end, we conducted a series of studies where we maintained the tubeworm, Ridgeia piscesae, in high-pressure aquaria and examined global and quantitative changes in gene expression via high-throughput transcriptomics and quantitative real-time PCR (qPCR). We analyzed over 32,000 full-length expressed sequence tags as well as 26 Mb of transcript sequences from the trophosome (the organ that houses the endosymbiotic bacteria) and the plume (the gas exchange organ in contact with the free-living microbial community). R. piscesae maintained under conditions that promote chemoautotrophy expressed a number of putative cell signaling and innate immunity genes, including pattern recognition receptors (PRRs), often associated with recognizing microbe-associated molecular patterns (MAMPs). Eighteen genes involved with innate immunity, cell signaling, cell stress and metabolite exchange were further analyzed using qPCR. PRRs, including five peptidoglycan recognition proteins and a Toll-like receptor, were expressed significantly higher in the trophosome compared to the plume. Although PRRs are often associated with mediating host responses to infection by pathogens, the differences in expression between the plume and trophosome also implicate similar mechanisms of microbial recognition in interactions between the host and symbiont. We posit that regulation of this association involves a molecular "dialogue" between the partners that includes interactions between the host's innate immune system and the symbiont.

TaDAD2, a negative regulator of programmed cell death, is important for the interaction between wheat and the stripe rust fungus

Defender against cell death (DAD) genes are known to function as negative regulators of cell death in animals. In plants, DAD orthologs are conserved but their role in cell death regulation is not well understood. Here, we report the characterization of the TaDAD2 gene in wheat. The predicted amino acid sequence of TaDAD2 contains typical structural features of DAD proteins, including a signal peptide, three transmembrane regions, and a subunit of oligosaccharyltransferase. Transcripts of TaDAD2 were detected in wheat leaves, culms, roots, florets, and spikelets. The expression level of TaDAD2 was reduced in the initial contact with the stripe rust fungus, subsequently induced and peaked at 18 h postinoculation (hpi), gradually reduced at 24 to 48 hpi, and restored to control level at 72 to 120 hpi. In addition, TaDAD2 exhibited positive transcriptional responses to abiotic stresses after the initial reduction at 1 hpi. Overexpression of TaDAD2 in tobacco leaves inhibited cell death. Furthermore, knocking down TaDAD2 expression by virus-induced gene silencing enhanced the susceptibility of wheat cv. Suwon11 to avirulent race CYR23 and reduced necrotic area at the infection sites. These results indicate that TaDAD2 may function as a suppressor of cell death in the early stages of wheat-stripe rust fungus interaction. However, it is dispensable for or plays an opposite role in hypersensitive response or cell death triggered by an avirulent race of stripe rust fungus at late-infection stages.

Sequence specific 1H, 13C and 15N backbone resonance assignments of UVI31+ from Chlamydomonas reinhardtii

The cDNA of UVI31+ was cloned from C. reinhardtii and expressed in E. coli from where the protein was purified to homogeneity. The purified protein exhibited beta-lactamase activity (Manuscript in preparation). However, UVI31+ has no homology with the known β-lactamases. In order to understand the structural basis of the ability of UVI31+ to hydrolyze β-lactam antibiotics, we in parallel, set out to structurally characterize it by NMR. Its β-lactamase activity in relation to the solution structure by NMR is likely to provoke deeper understanding of its mechanism and facilitate the rationalization of other functions of the protein, if any. In this endeavor, we report almost complete sequence-specific backbone (1)H, (13)C and (15)N NMR assignments of UVI31+.

Devil inside: does plant programmed cell death involve the endomembrane system?

Eukaryotic cells have to constantly cope with environmental cues and integrate developmental signals. Cell survival or death is the only possible outcome. In the field of animal biology, tremendous efforts have been put into the understanding of mechanisms underlying cell fate decision. Distinct organelles have been proven to sense a broad range of stimuli and, if necessary, engage cell death signalling pathway(s). Over the years, forward and reverse genetic screens have uncovered numerous regulators of programmed cell death (PCD) in plants. However, to date, molecular networks are far from being deciphered and, apart from the autophagic compartment, no organelles have been assigned a clear role in the regulation of cellular suicide. The endomembrane system (ES) seems, nevertheless, to harbour a significant number of cell death mediators. In this review, the involvement of this system in the control of plant PCD is discussed in-depth, as well as compared and contrasted with what is known in animal and yeast systems.

RNA-seq analysis of sulfur-deprived Chlamydomonas cells reveals aspects of acclimation critical for cell survival

The Chlamydomonas reinhardtii transcriptome was characterized from nutrient-replete and sulfur-depleted wild-type and snrk2.1 mutant cells. This mutant is null for the regulatory Ser-Thr kinase SNRK2.1, which is required for acclimation of the alga to sulfur deprivation. The transcriptome analyses used microarray hybridization and RNA-seq technology. Quantitative RT-PCR evaluation of the results obtained by these techniques showed that RNA-seq reports a larger dynamic range of expression levels than do microarray hybridizations. Transcripts responsive to sulfur deprivation included those encoding proteins involved in sulfur acquisition and assimilation, synthesis of sulfur-containing metabolites, Cys degradation, and sulfur recycling. Furthermore, we noted potential modifications of cellular structures during sulfur deprivation, including the cell wall and complexes associated with the photosynthetic apparatus. Moreover, the data suggest that sulfur-deprived cells accumulate proteins with fewer sulfur-containing amino acids. Most of the sulfur deprivation responses are controlled by the SNRK2.1 protein kinase. The snrk2.1 mutant exhibits a set of unique responses during both sulfur-replete and sulfur-depleted conditions that are not observed in wild-type cells; the inability of this mutant to acclimate to S deprivation probably leads to elevated levels of singlet oxygen and severe oxidative stress, which ultimately causes cell death. The transcriptome results for wild-type and mutant cells strongly suggest the occurrence of massive changes in cellular physiology and metabolism as cells become depleted for sulfur and reveal aspects of acclimation that are likely critical for cell survival.