Light-dependent subcellular localization of nucleoside diphosphate kinase-1 inNeurospora crassa

Nucleoside Diphosphate Kinase FgNdpk Is Required for DON Production and Pathogenicity by Regulating the Growth and Toxisome Formation of Fusarium graminearum

Nucleoside diphosphate kinases (NDPKs) are nucleotide metabolism enzymes that play different physiological functions in different species. However, the roles of NDPK in phytopathogen and mycotoxin production are not well understood. In this study, we showed that Fusarium graminearum FgNdpk is important for vegetative growth, conidiation, sexual development, and pathogenicity. Furthermore, FgNdpk is required for deoxynivalenol (DON) production; deletion of FgNDPK downregulates the expression of DON biosynthesis genes and disrupts the formation of FgTri4-GFP-labeled toxisomes, while overexpression of FgNDPK significantly increases DON production. Interestingly, FgNdpk colocalizes with the DON biosynthesis proteins FgTri1 and FgTri4 in the toxisome, and coimmunoprecipitation (Co-IP) assays show that FgNdpk associates with FgTri1 and FgTri4 in vivo and regulates their localizations and expressions, respectively. Taken together, these data demonstrate that FgNdpk is important for vegetative growth, conidiation, and pathogenicity and acts as a key protein that regulates toxisome formation and DON biosynthesis in F. graminearum.

Role of Trypanosoma cruzi nucleoside diphosphate kinase 1 in DNA damage responses

BACKGROUND

NME23/NDPKs are well conserved proteins found in all living organisms. In addition to being nucleoside diphosphate kinases (NDPK), they are multifunctional enzymes involved in different processes such as DNA stability, gene regulation and DNA repair among others. TcNDPK1 is the canonical NDPK isoform present in Trypanosoma cruzi, which has nuclease activity and DNA-binding properties in vitro.

OBJECTIVES

In the present study we explored the role of TcNDPK1 in DNA damage responses.

METHODS

TcNDPK1 was expressed in mutant bacteria and yeasts and over-expressed in epimastigotes. Mutation frequencies, tolerance to genotoxic agents and activity of DNA repair enzymes were evaluated.

FINDINGS

Bacteria decreased about 15-folds the spontaneous mutation rate and yeasts were more resistant to hydrogen peroxide and to UV radiation than controls. Parasites overexpressing TcNDPK1 were able to withstand genotoxic stresses caused by hydrogen peroxide, phleomycin and hidroxyurea. They also presented less genomic damage and augmented levels of poly(ADP)ribose and poly(ADP)ribose polymerase, an enzyme involved in DNA repair.

MAIN CONCLUSION

These results strongly suggest a novel function for TcNDPK1; its involvement in the maintenance of parasite’s genome integrity.

Nucleoside diphosphate kinase (Ndk): A pleiotropic effector manipulating bacterial virulence and adaptive responses

Nucleoside diphosphate kinase (Ndk) is a housekeeping enzyme that balances cellular nucleoside triphosphate (NTP) pools by catalyzing the reversible transfer of γ-phosphate from NTPs to nucleoside diphosphates (NDPs). In addition to its fundamental role in nucleotide metabolism, Ndk has roles in protein histidine phosphorylation, DNA cleavage/repair, and gene regulation. Recent studies have also revealed that Ndk secreted from bacteria is important in modulating virulence-associated phenotypes including quorum sensing regulation, type III secretion system activation, and virulence factor production. Moreover, after infection, Ndks released from bacteria are involved in regulating host defense activities, such as cell apoptosis, phagocytosis, and inflammatory responses. Given that Ndk exerts a pleiotropic effect on bacterial virulence and bacteria-host interactions, the biological significance of the bacterial Ndks during infection is intriguing. This review will provide a synopsis of the current knowledge regarding the biological properties and roles of Ndks in regulating bacterial virulence and adaptation and will discuss in depth the biological significance of Ndk during bacteria-host interactions.

Cytosolic Trypanosoma cruzi nucleoside diphosphate kinase generates large granules that depend on its quaternary structure

Nucleoside diphosphate kinase (NDPK) is a key enzyme in the control of cellular concentrations of nucleoside triphosphates, and has been shown to play important roles in many cellular processes. In this work we investigated the subcellular localization of the canonical NDPK1 from Trypanosoma cruzi (TcNDPK1), the etiological agent Chagas's Disease, and evaluated the effect of adding an additional weak protein-protein interaction domain from the green fluorescent protein (GFP). Immunofluorescence microscopy revealed that the enzyme from wild-type and TcNDPK1 overexpressing parasites has a cytosolic distribution, being the signal more intense around the nucleus. However, when TcNDPK1 was fused with dimeric GFP it relocalizes in non-membrane bounded granules also located adjacent to the nucleus. In addition, these granular structures were dependent on the quaternary structure of TcNDPK1 and GFP since mutations in residues involved in their oligomerization dramatically decrease the amount of granules. This phenomenon seems to be specific for TcNDPK1 since other cytosolic hexameric enzyme from T. cruzi, such as the NADP(+)-linked glutamate dehydrogenase, was not affected by the fusion with GFP. In addition, in parasites without GFP fusions granules could be observed in a subpopulation of epimastigotes under metacyclogenesis and metacyclic trypomastigotes. Organization into higher protein arrangements appears to be a singular feature of canonical NDPKs; however the physiological function of such structures requires further investigation.

Differential proteomic analysis of grapevine leaves by iTRAQ reveals responses to heat stress and subsequent recovery

BACKGROUND

High temperature is a major environmental factor limiting grape yield and affecting berry quality. Thermotolerance includes the direct response to heat stress and the ability to recover from heat stress. To better understand the mechanism of the thermotolerance of Vitis, we combined a physiological analysis with iTRAQ-based proteomics of Vitis vinifera cv Cabernet Sauvignon, subjected to 43°C for 6 h, and then followed by recovery at 25/18°C.

RESULTS

High temperature increased the concentrations of TBARS and inhibited electronic transport in photosynthesis apparatus, indicating that grape leaves were damaged by heat stress. However, these physiological changes rapidly returned to control levels during the subsequent recovery phase from heat stress. One hundred and seventy-four proteins were differentially expressed under heat stress and/or during the recovery phase, in comparison to unstressed controls, respectively. Stress and recovery conditions shared 42 proteins, while 113 and 103 proteins were respectively identified under heat stress and recovery conditions alone. Based on MapMan ontology, functional categories for these dysregulated proteins included mainly photosynthesis (about 20%), proteins (13%), and stress (8%). The subcellular localization using TargetP showed most proteins were located in the chloroplasts (34%), secretory pathways (8%) and mitochondrion (3%).

CONCLUSION

On the basis of these findings, we proposed that some proteins related to electron transport chain of photosynthesis, antioxidant enzymes, HSPs and other stress response proteins, and glycolysis may play key roles in enhancing grapevine adaptation to and recovery capacity from heat stress. These results provide a better understanding of the proteins involved in, and mechanisms of thermotolerance in grapevines.

Differential induction of mitochondrial machinery by light intensity correlates with changes in respiratory metabolism and photorespiration in rice leaves

The light responsiveness of mitochondrial function was investigated through changes in mitochondrial composition and metabolism in rice (Oryza sativa) shoots. The mitochondrial proteome and metabolite abundances under low light, (LL, 100 μmol m(-2) s(-1) ), and high light (HL, 700 μmol m(-2) s(-1) ) were measured along with information on shoot photosynthetic, respiratory and photorespiratory activity. Specific steps in mitochondrial tricarboxylic acid (TCA) cycle metabolism were decreased under HL, correlating with lower respiration rate under HL. The abundance of mitochondrial enzymes in branch chain metabolism was reduced under HL/LL, and correlated with a decrease in the abundance of a range of amino acids in the HL/LL. Mitochondrial nucleoside diphosphate kinase was increased under LL/HL treatments. Significant accumulation of glycine decarboxylase P, T subunits and serine hydroxymethyltransferase occurred in response to light. The abundance of the glycine decarboxylase (GDC) H subunit proteins was not changed by HL/LL treatments, and the abundance of GDC L subunit protein was halved under HL, indicating a change in the stoichiometry of GDC subunits, while photorespiration was fourfold higher in LL- than in HL-treated plants. Insights into these light-dependent phenomena and their importance for understanding the initiation of photorespiration in rice and adaptation of mitochondria to function in photosynthetic cells are discussed.

Differential induction of mitochondrial machinery by light intensity correlates with changes in respiratory metabolism and photorespiration in rice leaves

The light responsiveness of mitochondrial function was investigated through changes in mitochondrial composition and metabolism in rice (Oryza sativa) shoots. The mitochondrial proteome and metabolite abundances under low light, (LL, 100 μmol m(-2) s(-1) ), and high light (HL, 700 μmol m(-2) s(-1) ) were measured along with information on shoot photosynthetic, respiratory and photorespiratory activity. Specific steps in mitochondrial tricarboxylic acid (TCA) cycle metabolism were decreased under HL, correlating with lower respiration rate under HL. The abundance of mitochondrial enzymes in branch chain metabolism was reduced under HL/LL, and correlated with a decrease in the abundance of a range of amino acids in the HL/LL. Mitochondrial nucleoside diphosphate kinase was increased under LL/HL treatments. Significant accumulation of glycine decarboxylase P, T subunits and serine hydroxymethyltransferase occurred in response to light. The abundance of the glycine decarboxylase (GDC) H subunit proteins was not changed by HL/LL treatments, and the abundance of GDC L subunit protein was halved under HL, indicating a change in the stoichiometry of GDC subunits, while photorespiration was fourfold higher in LL- than in HL-treated plants. Insights into these light-dependent phenomena and their importance for understanding the initiation of photorespiration in rice and adaptation of mitochondria to function in photosynthetic cells are discussed.

Aspergillus fumigatus calcineurin interacts with a nucleoside diphosphate kinase

The Ca(2+)-calcineurin pathway affects virulence and morphogenesis in filamentous fungi. Here, we identified 37 CalA-interacting proteins that interact with the catalytic subunit of calcineurin (CalA) in Aspergillus fumigatus, including the nucleoside diphosphate kinase (SwoH). The in vivo interaction between CalA and SwoH was validated by bimolecular fluorescence complementation. A. fumigatus swoH is an essential gene. Therefore, a temperature-sensitive conditional mutant strain with a point mutation in the active site, SwoH(V83F), was constructed, which demonstrated reduced growth and increased sensitivity to elevated temperatures. The SwoH(V83F) mutation did not cause a loss in virulence in the Galleria mellonella infection model. Taken together these results imply that CalA interacts with SwoH.

Singular features of trypanosomatids' phosphotransferases involved in cell energy management

Trypanosomatids are responsible for economically important veterinary affections and severe human diseases. In Africa, Trypanosoma brucei causes sleeping sickness or African trypanosomiasis, while in America, Trypanosoma cruzi is the etiological agent of Chagas disease. These parasites have complex life cycles which involve a wide variety of environments with very different compositions, physicochemical properties, and availability of metabolites. As the environment changes there is a need to maintain the nucleoside homeostasis, requiring a quick and regulated response. Most of the enzymes required for energy management are phosphotransferases. These enzymes present a nitrogenous group or a phosphate as acceptors, and the most clear examples are arginine kinase, nucleoside diphosphate kinase, and adenylate kinase. Trypanosoma and Leishmania have the largest number of phosphotransferase isoforms ever found in a single cell; some of them are absent in mammals, suggesting that these enzymes are required in many cellular compartments associated to different biological processes. The presence of such number of phosphotransferases support the hypothesis of the existence of an intracellular enzymatic phosphotransfer network that communicates the spatially separated intracellular ATP consumption and production processes. All these unique features make phosphotransferases a promising start point for rational drug design for the treatment of human trypanosomiasis.

ROS resistance in Pisum sativum cv. Alaska: the involvement of nucleoside diphosphate kinase in oxidative stress responses via the regulation of antioxidants

This study investigated the reactive oxygen species (ROS) tolerance mechanism of a paraquat-resistant Pisum sativum line (R3-1) compared with the wild type (WT). Physiological and biochemical analyses showed significant differences in the phenotypes, such as delayed leaf and floral development, superior branching, and greater biomass and yields in the R3-1 line, as well as an increased level of antioxidant pigments and a lower rate of cellular lipid peroxidation in the resistant R3-1. Additionally, the phosphorylation of crude proteins showed distinguishable differences in band mobility and intensity between the R3-1 and WT plants. cDNA cloning and sequence analysis of NDPKs, which were candidate phosphorylated proteins, revealed that two of the deduced amino acids in NDPK2 (IL12L and Glu205Lys) and one in NDPK3 (P45S) were mutated in R3-1. Using glutathione S-transferase-NDPK fusion constructs, we found that the precursor recombinant R3-1 NDPK2 showed an increased level of activity and autophosphorylation in R3-1 plants compared to WT plants. Native PAGE analysis of the crude proteins revealed that NDPK and catalase (CAT) activity co-existed in the same area of the gel. In a yeast two-hybrid assay, the N-terminal region of NDPK2 showed an interaction with the full-length CAT1 protein. Furthermore, we found that WT showed a decreased level of CAT activity compared with R3-1 under illumination and/or on media containing ROS-releasing reagents. Taken together, these results suggest that there is a strong interaction between NDPK2 and CAT1 in R3-1 plants, which possibly plays a vital role in the antioxidant defense against ROS.

OXIDATIVE STRESS 3 is a chromatin-associated factor involved in tolerance to heavy metals and oxidative stress

A cDNA expression library from Brassica juncea was introduced into the fission yeast Schizosaccharomyces pombe to select for transformants tolerant to cadmium. Transformants expressing OXIDATIVE STRESS 3 (OXS3) or OXS3-Like cDNA exhibited enhanced tolerance to a range of metals and oxidizing chemicals. OXS3 belongs to a family of proteins that share a highly conserved domain corresponding to a putative N-acetyltransferase or thioltransferase catalytic site. Mutations within this conserved domain abolished the ability of Arabidopsis thaliana OXS3 to enhance stress tolerance in S. pombe, indicating a role in stress tolerance for the presumptive catalytic domain. A stress-sensitive mutant of AtOXS3 and enhanced tolerance of overexpression lines support the role of OXS3 in stress tolerance. The expression of tagged B. juncea and A. thaliana OXS3 proteins in plant cells revealed a subnuclear speckling pattern related to the nucleosome in discrete parts of the chromatin. It is possible that OXS3 might act as a chromatin remodeling factor for the stress response.

Involvement of OS-2 MAP kinase in regulation of the large-subunit catalases CAT-1 and CAT-3 in Neurospora crassa

Neurospora crassa has four catalase genes--cat-1, cat-2, cat-3, and ctt-1/cat-4. cat-1 and cat-3 encode two fungal-specific large-subunit catalases CAT-1 and CAT-3 normally produced in conidia and growing hyphae, respectively. cat-2 encodes CAT-2 catalase-peroxidase normally produced in conidia. ctt-1 (or cat-4), of which expression was controlled by OS-2 MAP kinase (Noguchi et al., Fungal Genet. Biol. 44, 208-218), encodes a small-subunit catalase with unknown function. To clarify the contribution of OS-2 on the regulation of CAT-1, CAT-2, and CAT-3, we performed quantitative RT-PCR and in-gel catalase activity analyses. When the hyphae were treated with a fungicide (1 mug/ml fludioxonil) or subjected to an osmotic stress (1 M sorbitol), cat-1 was strongly upregulated and CAT-1 was reasonably induced in the wild-type strain. Interestingly, fludioxonil caused not only the CAT-1 induction but also a remarkable CAT-3 decrease in the wild-type hyphae, implying of an abnormal stimulation of asexual differentiation. These responses were not observed in an os-2 mutant hyphae, indicating an involvement of OS-2 in the cat-1 expression; however, os-2 was dispensable for the production of CAT-1 in conidia. In contrast, the expression of cat-2 was significantly induced by heat shock (45 degrees C) and that of cat-3 was moderately stimulated by an oxidative stress (50 microg/ml methyl viologen) in both the wild-type strain and the os-2 mutant, and corresponding enzyme activities were detected after the treatments. Although basal levels of transcription of cat-1 and cat-3 in an os-2 mutant hyphae were a few-fold lower than in the wild-type hyphae, the os-2 mutant exhibited a considerably lower levels of CAT-3 activity than the wild-type strain. These findings suggest that OS-2 MAP kinase regulated the expression of cat-1 and cat-3 transcriptionally, and probably that of cat-3 posttranscriptionally, even though the presence of another regulatory system for each of these two genes is evident.

Impact of light on Hypocrea jecorina and the multiple cellular roles of ENVOY in this process

Background

In fungi, light is primarily known to influence general morphogenesis and both sexual and asexual sporulation. In order to expand the knowledge on the effect of light in fungi and to determine the role of the light regulatory protein ENVOY in the implementation of this effect, we performed a global screen for genes, which are specifically effected by light in the fungus Hypocrea jecorina (anamorph Trichoderma reesei) using Rapid Subtraction Hybridization (RaSH). Based on these data, we analyzed whether these genes are influenced by ENVOY and if overexpression of ENVOY in darkness would be sufficient to execute its function.

Results

The cellular functions of the detected light responsive genes comprised a variety of roles in transcription, translation, signal transduction, metabolism, and transport. Their response to light with respect to the involvement of ENVOY could be classified as follows: (i) ENVOY-mediated upregulation by light; (ii) ENVOY-independent upregulation by light; (iii) ENVOY-antagonized upregulation by light; ENVOY-dependent repression by light; (iv) ENVOY-independent repression by light; and (v) both positive and negative regulation by ENVOY of genes not responsive to light in the wild-type. ENVOY was found to be crucial for normal growth in light on various carbon sources and is not able to execute its regulatory function if overexpressed in the darkness.

Conclusion

The different responses indicate that light impacts fungi like H. jecorina at several cellular processes, and that it has both positive and negative effects. The data also emphasize that ENVOY has an apparently more widespread cellular role in this process than only in modulating the response to light.

Interaction of SOS2 with nucleoside diphosphate kinase 2 and catalases reveals a point of connection between salt stress and H2O2 signaling in Arabidopsis thaliana

SOS2, a class 3 sucrose-nonfermenting 1-related kinase, has emerged as an important mediator of salt stress response and stress signaling through its interactions with proteins involved in membrane transport and in regulation of stress responses. We have identified additional SOS2-interacting proteins that suggest a connection between SOS2 and reactive oxygen signaling. SOS2 was found to interact with the H2O2 signaling protein nucleoside diphosphate kinase 2 (NDPK2) and to inhibit its autophosphorylation activity. A sos2-2 ndpk2 double mutant was more salt sensitive than a sos2-2 single mutant, suggesting that NDPK2 and H2O2 are involved in salt resistance. However, the double mutant did not hyperaccumulate H2O2 in response to salt stress, suggesting that it is altered signaling rather than H2O2 toxicity alone that is responsible for the increased salt sensitivity of the sos2-2 ndpk2 double mutant. SOS2 was also found to interact with catalase 2 (CAT2) and CAT3, further connecting SOS2 to H2O2 metabolism and signaling. The interaction of SOS2 with both NDPK2 and CATs reveals a point of cross talk between salt stress response and other signaling factors including H2O2.

Catalase-1 (CAT-1) and nucleoside diphosphate kinase-1 (NDK-1) play an important role in protecting conidial viability under light stress in Neurospora crassa

Recently we reported that Catalase-1 (CAT-1) played an important role in protecting conidial viability in Neurospora crassa, and interacted with a light signal transducer, nucleoside diphosphate kinase-1 (NDK-1). To disclose the functional interaction between CAT-1 and NDK-1 at the genetic level, we created CAT-1 and NDK-1 double mutants, cat-1;ndk-1-1 and cat-1;ndk-1-2, by crossing single mutants of cat-1 ( RIP ) and ndk-1 ( P72H ) previously isolated in our laboratory. The double mutant strains grew normally, but showed increased CAT-2 activity. In cat-1 ( RIP ), NDK activity was increased when dCDP was used as a substrate. ndk-1 ( P72H ), cat-1;ndk-1-1, and cat-1;ndk-1-2 were more sensitive to riboflavin than the wild type and cat-1 ( RIP ) under strong light (100 microE m(-2) s(-1)). The pull-down experiment suggests that His-tagged NDK-1 is bound to [(32)P]NADH. However, his-tagged NDK-1(P72H) was not bound to [(32)P]NADH. The double mutants showed much lower conidial viability and lost all conidial germination ability much more rapidly than cat-1 ( RIP ), when they were cultured under continuous light for more than 2 weeks. These results indicate that the interaction of CAT-1 with NDK-1 plays an important role in supporting the survival of conidia under oxidative and light-induced stress including singlet oxygen, and confirm our former conclusion that reactive oxygen species play an important role in light signal transduction via NDK-1 at the genetic level.

Fungal photoreceptors: sensory molecules for fungal development and behaviour

Light regulates fungal development and behaviour and activates metabolic pathways. In addition, light is one of the many signals that fungi use to perceive and interact with the environment. In the ascomycete Neurospora crassa blue light is perceived by the white collar (WC) complex, a protein complex formed by WC-1 and WC-2. WC-1 is a protein with a flavin-binding domain and a zinc-finger domain, and interacts with WC-2, another zinc-finger domain protein. The WC complex operates as a photoreceptor and a transcription factor for blue-light responses in Neurospora. Proteins similar to WC-1 and WC-2 have been described in other fungi, suggesting a general role for the WC complex as a fungal receptor for blue light. The ascomycete Aspergillus nidulans uses red light perceived by a fungal phytochrome as a signal to regulate sexual and asexual development. In addition, other photoreceptors, rhodopsins and cryptochromes, have been identified in fungi, but their functional relevance has not been elucidated. The investigation of fungal light responses provides an opportunity to understand how fungi perceive the environment and to identify the mechanisms involved in the regulation by light of cellular development and metabolism.