Diurnal fluctuations in chloroplast GSH redox state regulate susceptibility to oxidative stress and cell fate in a bloom‐forming diatom

Abstract

Diatoms are one of the key phytoplankton groups in the ocean, forming vast oceanic blooms and playing a significant part in global primary production. To shed light on the role of redox metabolism in diatom's acclimation to light-dark transition and its interplay with cell fate regulation, we generated transgenic lines of the diatom Thalassiosira pseudonana that express the redox-sensitive green fluorescent protein targeted to various subcellular organelles. We detected organelle-specific redox patterns in response to oxidative stress, indicating compartmentalized antioxidant capacities. Monitoring the GSH redox potential (E ) in the chloroplast over diurnal cycles revealed distinct rhythmic patterns. Intriguingly, in the dark, cells exhibited reduced basal chloroplast E but higher sensitivity to oxidative stress than cells in the light. This dark-dependent sensitivity to oxidative stress was a result of a depleted pool of reduced glutathione which accumulated during the light period. Interestingly, reduction in the chloroplast E was observed in the light phase prior to the transition to darkness, suggesting an anticipatory phase. Rapid chloroplast E re-oxidation was observed upon re-illumination, signifying an induction of an oxidative signaling during transition to light that may regulate downstream metabolic processes. Since light-dark transitions can dictate metabolic capabilities and susceptibility to a range of environmental stress conditions, deepening our understanding of the molecular components mediating the light-dependent redox signals may provide novel insights into cell fate regulation and its impact on oceanic bloom successions.

Single-cell heterogeneity in the chloroplast redox state mediates acclimation to stress in a marine diatom

“…2 D), before the cell has accumulated damage beyond repair or a PCD cascade was fully activated. This "pre-commitment" phase was shown previously in two diatom species, as exogenous application of the antioxidant GSH rescued diatom cells from otherwise lethal treatments of infochemicals or H2O2 only during the first hour 16,18 . These findings underscore the importance of redox regulation in chloroplast metabolic reactions, and its involvement in stress sensing and cell fate determination.…”

“…Photosynthesis is the major source for reductive power as well as ROS in algal cells, and exposure to dark was shown to increase sensitivity to oxidative stress in another marine diatom 18 . Therefore, we hypothesized that light regime will affect the bi-stable pattern of chl-roGFP following oxidative stress, and investigated the effects of short exposure to darkness during daytime.…”

“…They are exposed to stress from different biotic and abiotic origins such as grazing, viruses, bacteria, allelopathic interactions, light availability, and nutrient limitations 7-14 . Importantly, induction of programmed cell death (PCD) in response to different stressors has been suggested as an important mechanism contributing to the fast turnover of phytoplankton and the rapid bloom demise 7,8,15 .Recent studies suggested that diatoms can differentially response to diverse environmental cues based on compartmentalized redox fluctuations that also mediate stress-induced PCD [16][17][18] . Reactive oxygen species (ROS) are known to play an important role in sensing stress and additional signals across kingdoms, from bacteria to plants and animals [19][20][21][22][23] .…”

“…Recent studies suggested that diatoms can differentially response to diverse environmental cues based on compartmentalized redox fluctuations that also mediate stress-induced PCD [16][17][18] . Reactive oxygen species (ROS) are known to play an important role in sensing stress and additional signals across kingdoms, from bacteria to plants and animals [19][20][21][22][23] .…”

Resolving the dynamics of photosynthetically produced ROS by high-resolution monitoring of chloroplastic EGSHinArabidopsis

“…Due to their high sensitivity, reversibility and insensitivity to pH alterations in the physiological range (Schwarzländer et al, 2008), such protein-based redox sensors are powerful tools for investigating redox dynamics in subcellular compartments. Recently, roGFPexpressing plants and algae have been tested under various biotic and abiotic stresses and had shown organelle-specific roGFP oxidation patterns (Rosenwasser et al, 2010;van Creveld et al, 2015;Bratt et al, 2016;Volpert et al, 2018;Mizrachi et al, 2019;Nietzel et al, 2019).…”