Exogenous Glutathione Promotes the Proliferation of Pinus koraiensis Embryonic Cells and the Synthesis of Glutathione and Ascorbic Acid

Evolutionary insights into strategy shifts for the safe and effective accumulation of ascorbate in plants

Plants accumulate high concentrations of ascorbate, commonly in their leaves, as a redox buffer. While ascorbate levels have increased during plant evolution, the mechanisms behind this phenomenon are unclear. Moreover, has the increase in ascorbate concentration been achieved without imposing any detrimental effects on the plants? In this review, we focus on potential transitions in two regulatory mechanisms related to ascorbate biosynthesis and the availability of cellular dehydroascorbate (DHA) during plant evolution. The first transition might be that the trigger for the transcriptional induction of VTC2, which encodes the rate-limiting enzyme in ascorbate biosynthesis, has shifted from oxidative stress (in green algae) to light/photosynthesis (in land plants), probably enabling the continuous accumulation of ascorbate under illumination. This could serve as a preventive system against the unpredictable occurrence of oxidative stress. The second transition might be that DHA-degrading enzymes, which protect cells from the highly reactive DHA in green algae and mosses, have been lost in ferns or flowering plants. Instead, flowering plants may have increased glutathione concentrations to reinforce the DHA reduction capacity, possibly allowing ascorbate accumulation and avoiding the toxicity of DHA. These potential transitions may have contributed to strategies for plants' safe and effective accumulation of ascorbate.

Transcriptomic and metabolomic analysis unveils a negative effect of glutathione metabolism on laccase activity in Cerrena unicolor 87613

The white rot fungus Cerrena unicolor 87613 has been previously shown to be a promising resource in laccase production, an enzyme with significant biotechnological applications. Conventional methods face technical challenges in improving laccase activity. Attempts are still being made to develop novel approaches for further enhancing laccase activity. This study aimed to understand the regulation of laccase activity in C. unicolor 87613 for a better exploration of the novel approach. Transcriptomic and metabolomic analyses were performed to identify key genes and metabolites involved in extracellular laccase activity. The findings indicated a strong correlation between the glutathione metabolism pathway and laccase activity. Subsequently, experimental verifications were conducted by manipulating the pathway using chemical approaches. The additive reduced glutathione (GSH) dose-dependently repressed laccase activity, while the GSH inhibitors (APR-246) and reactive oxygen species (ROS) inducer (H2O2) enhanced laccase activity. Changes in GSH levels could determine the intracellular redox homeostasis in interaction with ROS and partially affect the expression level of laccase genes in C. unicolor 87613 in turn. In addition, GSH synthetase was found to mediate GSH abundance in a feedback loop. This study suggests that laccase activity is negatively influenced by GSH metabolism and provides a theoretical basis for a novel strategy to enhance laccase activity by reprogramming glutathione metabolism at a specific cultivation stage.IMPORTANCEThe production of laccase activity is limited by various conventional approaches, such as heterologous expression, strain screening, and optimization of incubation conditions. There is an urgent need for a new strategy to meet industrial requirements more effectively. In this study, we conducted a comprehensive analysis of the transcriptome and metabolome of Cerrena unicolor 87613. For the first time, we discovered a negative role played by reduced glutathione (GSH) and its metabolic pathway in influencing extracellular laccase activity. Furthermore, we identified a feedback loop involving GSH, GSH synthetase gene, and GSH synthetase within this metabolic pathway. These deductions were confirmed through experimental investigations. These findings not only advanced our understanding of laccase activity regulation in its natural producer but also provide a theoretical foundation for a strategy to enhance laccase activity by reprogramming glutathione metabolism at a specific cultivation stage.

Proper doses of brassinolide enhance somatic embryogenesis in different competent Korean pine cell lines during embryogenic callus differentiation

Somatic embryogenesis of Korean pine (Pinus koraiensis Sieb. Et Zucc.), an ecologically and econimically very important conifer species, was hindered by the gradually weakens and fast runaway of the embryogenicity and embryo competence of the embryogenic callus. Brassinolide (BL) has shown the enhancing capability of somatic embryo regeneration. For checking the function of BL in this issue, we applied different concentrations of BL to Korean pine callus materials exhibiting different embryogenic capacities and subsequently monitored the physiological alterations and hormone dynamics of the embryogenic callus. Our study revealed that calli with different embryogenic strengths responded differently to different concentrations of BL, but the effect after the addition of BL was very uniform. The addition of BL during the proliferation phase of embryogenic callus may help to stimulate the biological activity of callus during the proliferation process and improve the level of cell metabolism, which is accompanied by a reduction in storage substances. BL could reduce the level of endogenous auxin IAA in embryogenic callus and increase the level of abscisic acid to regulate cell division and differentiation. In addition, the MDA content in the callus was significantly decreased and the activity of antioxidant enzymes was significantly increased after the addition of BL. During the proliferation of embryogenic callus, BL was added to participate in the metabolism of phenylpropane in the cells and to increase the activity of phenylalanine ammonia-lyase and the content of lignin in the cells. We deduced that the proper doses of BL for Korean pine embryogenic callus culture were as follow: calli with low, high and decreasing embryogenicity were subcultured after the addition of 0.75 mg/L, 0.35 mg/L, 2.00 mg/L BL, respectively, during proliferation culture stage.

Reactive oxygen metabolism in the proliferation of Korean pine embryogenic callus cells promoted by exogenous GSH

Exogenous glutathione (GSH) promotes the proliferation of embryogenic callus (EC) cells in Korean pine in the course of somatic embryogenesis, and reactive oxygen species (ROS) may play an important role in regulating the proliferation of EC cells by exogenous GSH. However, the concrete metabolic response of ROS is unclear. In this study, two cell lines of Korean pine with high proliferative potential 001#-001 (F, Fast proliferative potential cell line is abbreviated as F) and low proliferative potential 001#-010 (S, Slow proliferative potential cell line is abbreviated as S) were used as test materials. The responses of ROS-related enzymes and substances to exogenous GSH and L-Buthionine-sulfoximine (BSO) were investigated in EC cells. The results showed that the exogenous addition of GSH increased the number of early somatic embryogenesis (SEs) in EC cells of both F and S cell lines, decreased the amount of cell death in both cell lines. Exogenous addition of GSH promoted cell division in both cell lines, increased intracellular superoxide dismutase (SOD) and catalase (CAT) activities, inhibited intracellular hydrogen peroxide (H₂O₂), malondialdehyde (MDA) and nitric oxide (NO) production, and increased NO/ROS ratio. In conclusion, the exogenous GSH promoting the proliferation of Korean pine EC cells, the activity of intracellular antioxidant enzymes was enhanced, the ROS level was reduced, and the resistance of cells to stress was enhanced.