Metabolic and biochemical responses of Potamogeton anguillanus Koidz. (Potamogetonaceae) to low oxygen conditions

Plant Life with and without Oxygen: A Metabolomics Approach

Oxygen deficiency is an environmental challenge which affects plant growth, the development and distribution in land and aquatic ecosystems, as well as crop yield losses worldwide. The capacity to exist in the conditions of deficiency or the complete lack of oxygen depends on a number of anatomic, developmental and molecular adaptations. The lack of molecular oxygen leads to an inhibition of aerobic respiration, which causes energy starvation and the acceleration of glycolysis passing into fermentations. We focus on systemic metabolic alterations revealed with the different approaches of metabolomics. Oxygen deprivation stimulates the accumulation of glucose, pyruvate and lactate, indicating the acceleration of the sugar metabolism, glycolysis and lactic fermentation, respectively. Among the Krebs-cycle metabolites, only the succinate level increases. Amino acids related to glycolysis, including the phosphoglycerate family (Ser and Gly), shikimate family (Phe, Tyr and Trp) and pyruvate family (Ala, Leu and Val), are greatly elevated. Members of the Asp family (Asn, Lys, Met, Thr and Ile), as well as the Glu family (Glu, Pro, Arg and GABA), accumulate as well. These metabolites are important members of the metabolic signature of oxygen deficiency in plants, linking glycolysis with an altered Krebs cycle and allowing alternative pathways of NAD(P)H reoxidation to avoid the excessive accumulation of toxic fermentation products (lactate, acetaldehyde, ethanol). Reoxygenation induces the downregulation of the levels of major anaerobically induced metabolites, including lactate, succinate and amino acids, especially members of the pyruvate family (Ala, Leu and Val), Tyr and Glu family (GABA and Glu) and Asp family (Asn, Met, Thr and Ile). The metabolic profiles during native and environmental hypoxia are rather similar, consisting in the accumulation of fermentation products, succinate, fumarate and amino acids, particularly Ala, Gly and GABA. The most intriguing fact is that metabolic alterations during oxidative stress are very much similar, with plant response to oxygen deprivation but not to reoxygenation.

Metabolomic profiling of Marek's disease virus infection in host cell based on untargeted LC-MS

Marek's disease (MD) caused by Marek's disease virus (MDV), poses a serious threat to the poultry industry by inducing neurological disease and malignant lymphoma in infected chickens. However, the underlying mechanisms how MDV disrupts host cells and causes damage still remain elusive. Recently, the application of metabolomics has shown great potential for uncovering the complex mechanisms during virus-host interactions. In this study, chicken embryo fibroblasts (CEFs) infected with MDV were subjected to ultrahigh-performance liquid chromatography-quadrupole time-of-flight tandem mass spectrometry (UHPLC-QTOF-MS) and multivariate statistical analysis. The results showed that 261 metabolites were significantly altered upon MDV infection, with most changes occurring in amino acid metabolism, energy metabolism, nucleotide metabolism, and lipid metabolism. Notably, MDV infection induces an up-regulation of amino acids in host cells during the early stages of infection to provide the energy and intermediary metabolites necessary for efficient multiplication of its own replication. Taken together, these data not only hold promise in identifying the biochemical molecules utilized by MDV replication in host cells, but also provides a new insight into understanding MDV-host interactions.

Metabolomics Analysis of PK-15 Cells with Pseudorabies Virus Infection Based on UHPLC-QE-MS

Viruses depend on the metabolic mechanisms of the host to support viral replication. We utilize an approach based on ultra-high-performance liquid chromatography/Q Exactive HF-X Hybrid Quadrupole-Orbitrap Mass (UHPLC-QE-MS) to analyze the metabolic changes in PK-15 cells induced by the infections of the pseudorabies virus (PRV) variant strain and Bartha K61 strain. Infections with PRV markedly changed lots of metabolites, when compared to the uninfected cell group. Additionally, most of the differentially expressed metabolites belonged to glycerophospholipid metabolism, sphingolipid metabolism, purine metabolism, and pyrimidine metabolism. Lipid metabolites account for the highest proportion (around 35%). The results suggest that those alterations may be in favor of virion formation and genome amplification to promote PRV replication. Different PRV strains showed similar results. An understanding of PRV-induced metabolic reprogramming will provide valuable information for further studies on PRV pathogenesis and the development of antiviral therapy strategies.

Hydrogen Peroxide Variation Patterns as Abiotic Stress Responses of Egeria densa

In vegetation management, understanding the condition of submerged plants is usually based on long-term growth monitoring. Reactive oxygen species (ROS) accumulate in organelles under environmental stress and are highly likely to be indicators of a plant's condition. However, this depends on the period of exposure to environmental stress, as environmental conditions are always changing in nature. Hydrogen peroxide (H2O2) is the most common ROS in organelles. The responses of submerged macrophytes, Egeria densa, to high light and iron (Fe) stressors were investigated by both laboratory experiments and natural river observation. Plants were incubated with combinations of 30-200 μmol m-2 s-1 of photosynthetically active radiation (PAR) intensity and 0-10 mg L-1 Fe concentration in the media. We have measured H2O2, photosynthetic pigment concentrations, chlorophyll a (Chl-a), chlorophyll b (Chl-b), carotenoid (CAR), Indole-3-acetic acid (IAA) concentrations of leaf tissues, the antioxidant activity of catalase (CAT), ascorbic peroxidase (APX), peroxidase (POD), the maximal quantum yield of PSII (Fv Fm -1), and the shoot growth rate (SGR). The H2O2 concentration gradually increased with Fe concentration in the media, except at very low concentrations and at an increased PAR intensity. However, with extremely high PAR or Fe concentrations, first the chlorophyll contents and then the H2O2 concentration prominently declined, followed by SGR, the maximal quantum yield of PSII (Fv Fm -1), and antioxidant activities. With an increasing Fe concentration in the substrate, the CAT and APX antioxidant levels decreased, which led to an increase in H2O2 accumulation in the plant tissues. Moreover, increased POD activity was proportionate to H2O2 accumulation, suggesting the low-Fe independent nature of POD. Diurnally, H2O2 concentration varies following the PAR variation. However, the CAT and APX antioxidant activities were delayed, which increased the H2O2 concentration level in the afternoon compared with the level in morning for the same PAR intensities. Similar trends were also obtained for the natural river samples where relatively low light intensity was preferable for growth. Together with our previous findings on macrophyte stress responses, these results indicate that H2O2 concentration is a good indicator of environmental stressors and could be used instead of long-term growth monitoring in macrophyte management.

African swine fever virus regulates host energy and amino acid metabolism to promote viral replication

African swine fever is one of the most serious viral diseases caused by African swine fever virus (ASFV). The metabolic changes induced by ASFV infection remain unknown. Here, PAMs infected with ASFV was analyzed by ultra-high-performance liquid chromatography/quadrupole time-of-flight tandem mass spectrometry (UHPLC-QTOF-MS) in combination with multivariate statistical analysis. A total of 90 metabolites were significantly changed after ASFV infection, and most of them belong to amino acids and TCA cycle intermediates. ASFV infection induced increase of most of amino acids in host during the early stages of infection, and amino acids decreased in the late stages of infection. ASFV infection did not significantly affected glycolysis pathway, whereas it induced the increase of citrate, succinate, α-ketoglutarate, and oxaloacetate levels in the TCA cycle, suggesting that ASFV infection promoted TCA cycle. The activity of aspartate aminotransferase and glutamate production were significantly elevated in ASFV-infected cells and pigs, resulting in reversible transition between TCA cycle and amino acids synthesis. Aspartate, glutamate, and TCA cycle were essential for ASFV replication. In addition, ASFV infection induced an increase in lactate level using lactate dehydrogenase, which led to low expression of IFN-β and increased of ASFV replication. Our data, for the first time, indicated that ASFV infection controls IFN-β production through RIG-I-mediated signaling pathways. These data identified a novel mechanism evolved by ASFV to inhibit host innate immune responses, and will provide insights for development of new preventive or therapeutic strategies targeting the altered metabolic pathways. IMPORTANCE In order to promote viral replication, viruses often cause severe immunosuppression and seize organelles to synthesize a large number of metabolites required for self-replication. African swine fever virus (ASFV) has developed many strategies to evade host innate immune responses. However, the impact of ASFV infection on host cellular metabolism remains unknown. Here, for the first time, we analyzed the metabolomic profiles of ASFV-infected PAMs cells. ASFV infection increased host TCA cycle and amino acids metabolism. Aspartate, glutamate, and TCA cycle promoted ASFV replication. ASFV infection also induced the increase of lactate production to inhibit innate immune responses for self-replication. This study identified novel immune evasion mechanisms utilized by ASFV and provided viewpoints on ASFV-host interactions, which is critical for guiding the design of new prevention strategies against ASFV targeting the altered metabolic pathways.

In Vitro and In Vivo Metabolomic Profiling after Infection with Virulent Newcastle Disease Virus

Newcastle disease (ND) is an acute, febrile, highly contagious disease caused by the virulent Newcastle disease virus (vNDV). The disease causes serious economic losses to the poultry industry. However, the metabolic changes caused by vNDV infection remain unclear. The objective of this study was to determine the metabolomic profiling after infection with vNDV. DF-1 cells infected with the vNDV strain Herts/33 and the lungs from Herts/33-infected specific pathogen-free (SPF) chickens were analyzed via ultra-high-performance liquid chromatography/quadrupole time-of-flight tandem mass spectrometry (UHPLC-QTOF-MS) in combination with multivariate statistical analysis. A total of 305 metabolites were found to have changed significantly after Herts/33 infection, and most of them belong to the amino acid and nucleotide metabolic pathway. It is suggested that the increased pools of amino acids and nucleotides may benefit viral protein synthesis and genome amplification to promote NDV infection. Similar results were also confirmed in vivo. Identification of these metabolites will provide information to further understand the mechanism of vNDV replication and pathogenesis.