Ascorbate peroxidase (APX; EC 1.11.1.11) activity and transcript levels of CrAPX1, CrAPX2, and CrAPX4 of Chlamydomonas reinhardtii increased under 1,400 μE•m −2 •s −1 condition (HL). CrAPX4 expression was the most significant. So, CrAPX4 was downregulated using amiRNA technology to examine the role of APX for HL acclimation. The CrAPX4 knockdown amiRNA lines showed low APX activity and CrAPX4 transcript level without a change in CrAPX1 and CrAPX2 transcript levels, and monodehydroascorbate reductase (MDAR), dehydroascorbate reductase (DHAR), and glutathione reductase (GR) activities and transcript levels. Upon exposure to HL, CrAPX4 knockdown amiRNA lines appeared a modification in the expression of genes encoding the enzymes in the ascorbateglutathione cycle, including an increase in transcript level of CrVTC2, a key enzyme for ascorbate (AsA) biosynthesis but a decrease in MDAR and DHAR transcription and activity after 1 h, followed by increases in reactive oxygen species production and lipid peroxidation after 6 h and exhibited cell death after 9 h. Besides, AsA content and AsA/DHA (dehydroascorbate) ratio decreased in CrAPX4 knockdown amiRNA lines after prolonged HL treatment. Thus, CrAPX4 induction together with its association with the modulation of MDAR and DHAR expression for AsA regeneration is critical for Chlamydomonas to cope with photo-oxidative stress. Reactive oxygen species (ROS) are generated in plants upon exposure to stressful conditions 1. Upon high intensity illumination, the photosynthetic electron transport components will be over-reduced, and O 2 will be photoreduced via photosystem I and photosystem II for formation of ROS 2 , which oxidize macromolecules (lipids, proteins, and nucleic acids) and subsequently impact cellular metabolism and physiological performance 3. To counter the ROS-induced oxidative stress, plants have developed the antioxidative defense system encompassing antioxidants and antioxidative enzymes, such as ascorbate (AsA) and ascorbate peroxidase (APX; EC 1.11.1.11). APX, which is the first step of the AsA-glutathione (GSH) cycle, uses AsA as its specific electron donor to reduce H 2 O 2 to water. APX, a central enzyme for ROS scavenging in plants 4,5 , can be induced under abiotic and biotic stresses 6-11. Salt stress can increase OsAPX2 and OsAPX7 transcript levels but decreases OsAPX8 transcript level in rice 12 while drought stress also increases APX transcript level in rice 13 and wheat 14. Transcript levels of APXs in potato tubers 15 , rice 7 , and Arabidopsis 11 are also induced by low temperature exposure. The cytosolic APX (APX1 and APX2) transcript level in Arabidopsis thaliana also increases by excess light illumination at 2,000 μE•m −2 •s −1 within 15 min and reaches the maximum after 60 min, followed by a decrease 16. This rapid increase is associated with the signal derived from a change in redox status of the plastoquinone pool caused by photoinhibition under high light condition. In spinach, the transcript level, protein level, and enzyme activity of c...
Autophagy plays a role in regulating important cellular functions in response to stress conditions. The role of nitric oxide (NO) in the regulation of autophagy in Chlamydomonas reinhardtii has been not studied. Illumination of C. reinhardtii cells under a high light (HL, 1,600 µmol m −2 s −1) condition induced a NO burst through NO synthase-and nitrate reductase-independent routes, and cell death. The abundance of CrATG8 protein, an autophagy marker of C. reinhardtii, increased after HL illumination along with a linear increase in the transcript abundance of autophagy-associated genes (CrVPS34, CrATG1, CrATG3, CrATG4, CrATG6, CrATG7, CrATG8, and CrATG12), which were suppressed in the presence of an NO scavenger, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO). The cells were treated with NO donors, S-nitroso-N-acetyl-penicillamine, and S-nitrosoglutathione, under a normal light (50 µmol m −2 s −1) condition to elucidate the role of NO in autophagy activation and cell death. Treatment with 0.05 mM or 0.1 mM NO donors increased the abundance of ATG8 protein and CrATG transcripts, which were suppressed in the presence of cPTIO. Moreover, treatment with 0.05 mM NO donors did not affect cell viability, while 0.1 mM NO donors elicited a transient decrease in cell growth and death that recovered after 12 h. The transient effect could be prevented by the presence of cPTIO. However, treatment with 1 mM H 2 O 2 and 0.1 mM NO donors enhanced autophagy induction and resulted in cell death after 24 h. The interaction of H 2 O 2 and NO can be prevented by cPTIO treatment. This implies that NO is critical for the interaction of H 2 O 2 and NO that induces cell death and autophagy. Furthermore, exposure to 0.1 mM NO donors under a non-lethal HL condition (750 µmol m −2 s −1) evoked autophagy and cell death. In conclusion, the present findings demonstrated that the NO-mediated autophagy pathway is activated in C. reinhardtii under lethal high intensity illumination and may interact with H 2 O 2 for HL-induced cell death. The relationships between autophagy and cell death are discussed.
Microalgae, a group of photosynthetic microorganisms rich in diverse and novel bioactive metabolites, have been explored for the production of biofuels, high value-added compounds as food and feeds, and pharmaceutical chemicals as agents with therapeutic benefits. This article reviews the development of omics resources and genetic engineering techniques including gene transformation methodologies, mutagenesis, and genome-editing tools in microalgae biorefinery and wastewater treatment (WWT).The introduction of these enlisted techniques has simplified the understanding of complex metabolic pathways undergoing microalgal cells. The multiomics approach of the integrated omics datasets, big data analysis, and machine learning for the discovery of objective traits and genes responsible for metabolic pathways was reviewed. Recent advances and limitations of multiomics analysis and genetic bioengineering technology to facilitate the improvement of microalgae as the dual role of WWT and biorefinery feedstock production are discussed.
The acclimation mechanism of Chlamydomonas reinhardtii to nitric oxide (NO) was studied by exposure to S-nitroso-N-acetylpenicillamine (SNAP), a NO donor. Treatment with 0.1 or 0.3 mM SNAP transiently inhibited photosynthesis within 1 h, followed by a recovery, while 1.0 mM SNAP treatment caused irreversible photosynthesis inhibition and mortality. The SNAP effects are avoided in the presence of the NO scavenger, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-l-oxyl-3-oxide (cPTIO). RNA-seq, qPCR, and biochemical analyses were conducted to decode the metabolic shifts under NO stress by exposure to 0.3 mM SNAP in the presence or absence of 0.4 mM cPTIO. These findings revealed that the acclimation to NO stress comprises a temporally orchestrated implementation of metabolic processes: (1). modulation of NADPH oxidase (respiratory burst oxidase-like 2, RBOL2) and ROS signaling pathways for downstream mechanism regulation, (2). trigger of NO scavenging elements to reduce NO level; (3). prevention of photo-oxidative risk through photosynthesis inhibition and antioxidant defense system induction; (4). acclimation to nitrogen and sulfur shortage; (5). attenuation of transcriptional and translational activity together with degradation of damaged proteins through protein trafficking machinery (ubiquitin, SNARE, and autophagy) and molecular chaperone system for dynamic regulation of protein homeostasis. In addition, the expression of the gene encoding NADPH oxidase, RBOL2, showed a transient increase while that of RBOL1 was slightly decreased after NO challenge. It reflects that NADPH oxidase, a regulator in ROS-mediated signaling pathway, may be involved in the responses of Chlamydomonas to NO stress. In conclusion, our findings provide insight into the molecular events underlying acclimation mechanisms in Chlamydomonas to NO stress.
Nitric oxide (NO) is a signal in the modulation of acclamatory responses to stress in plants. Here, the metabolic shift of Chlamydomonas reinhardtii to sub-lethal NO stress was approached by exposure to 0.1 mM S-nitroso-N-acetylpenicillamine (SNAP), a NO donor, in the presence or the absence of the NO scavenger, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-l-oxyl-3-oxide (cPTIO). NO did not cause growth impairment but induced a decrease in glutathione (GSH) levels and redox state. NO upregulated the expression of glutathione-associated genes, glutathione synthetase (GSH1), and glutathione reductase (GSHR1) genes while it decreased that of the proteins associated with ER stress-induced unfolded protein response (UPR). Furthermore, the expression of NADPH oxidase isoform, respiratory burst oxygenase-like 2 (RBOL2), instead of RBOL1 increased under NO stress. NO-induced upregulation of GSH1 and GSHR1 upregulation and the downregulation of most UPR genes were not found in rbol2 mutant. The presence of cPTIO suppressed the NO-induced changes in GSH availability, UPR, and RBOL expression. Overall, NADPH oxidase (RBOL2)-dependent and -independent signaling pathways involve in the inhibition of UPR and the enhancement of GSH availability by NO.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.