Biology subjects

Tamanna, S. S.

Publications and source records attributed to Tamanna, S. S..

3 recordsLinked to original sources

bioRxiv2026

Loss of ELM1B impairs mitochondrial fission, matrix redox state and stress tolerance in Physcomitrium patens

Mitochondria are endosymbiont-derived organelles that play a central role in cellular metabolism, energy production and stress responses. While single mitochondria represent functional units, they continuously exchange their contents through fusion and fission, facing stress conditions as a dynamic population. To date, it remains largely unknown how stress alters mitochondrial dynamics in plants and how altered dynamics affect mitochondrial properties and plant stress resilience. Here, we investigate mitochondrial dynamics in response to oxidative stress in the non vascular model plant Physcomitrium patens. By creating mutants with impaired mitochondrial fission in different reporter lines for mitochondrial parameters, we additionally analyse effects of chronic changes to mitochondrial population dynamics. We found that Mito-Paraquat (MtPQ) treatment increased the glutathione redox potential EGSH in mitochondria, the cytosol and chloroplasts, as monitored via roGFP2-based genetically encoded biosensors. Mitochondria elongated within hours and showed a concomitant and heterogenous increase of matrix EOSred, that we propose as a marker for matrix protein damage. Mitochondrial fission mutants lacking PpELM1B (ELONGATED MITOCHONDRIA) displayed distinct changes of mitochondrial morphology parameters as determined by automated 3D-segmentation and feature mapping (MorphoMapper) of confocal z-stacks. Elongated mitochondria in Ppelm1bge lines showed an oxidative matrix EGSH shift and increased matrix EOSred while matrix mixing still occurred, albeit at the same slow rate as in wildtype, within days. Macroscopically, Ppelm1bge lines displayed reduced growth, decreased respiration, and a higher sensitivity to oxidative stress. Our results show that plant mitochondrial morphology and physiological parameters specifically shift in response to stress and impaired fission. Mitochondrial fission is vital to maintain a healthy mitochondrial population that sustains plant oxidative stress tolerance.

plant biology↗

bioRxiv2024

Early-branching cyanobacteria up-regulate superoxide dismutase activity under a simulated early Earth anoxic atmosphere.

The evolution of oxygenic photosynthesis during the Archean (4-2.5 Ga), required the presence of complementary reducing pathways to maintain the cellular redox balance. While the timing of the evolution of superoxide dismutases (SODs), enzymes that convert superoxide to hydrogen peroxide, within the Bacteria and Archaea is not resolved, SODs containing copper and zinc in the reaction centre (CuZnSOD) were the first SODs estimated to appear in photosynthetic cyanobacteria, [≥] 2.93 Ga. Here we analysed the SOD gene expression and activity in the deep branching strain, Pseudanabaena sp. PCC7367. It releases more O2 and exhibits significantly higher growth rates (p<0.001) and protein and glycogen contents (p<0.05) under anoxic conditions compared to control cultures grown under present oxygen rich atmospheres in low CO2 (LC) or high CO2 (HC), prompting the question as to whether this correlates to higher cellular SOD activity under anoxic Archean simulated conditions. Expression of sodB encoding an iron containing SOD (FeSOD) and sodC, encoding a CuZnSOD, strongly correlated with increased extracellular O2 levels (p<0.001), while transcription of sodA, encoding a manganese containing (MnSOD), correlated to SOD activity during the day (p=0.019), when medium O2 concentrations were the highest. Cytosolic SOD activity was significantly higher (p<0.001) in anoxic cultures, two hrs before nightfall compared to oxic growth conditions. Night-time combined sodABC transcription in stirred cultures was significantly reduced (p<0.05) under anoxic conditions at elevated CO2 levels, as were medium O2 levels (p[≤]0.001), when compared to cultures grown under present-day oxic conditions with low CO2. Total cytosolic SOD activity remained comparable, suggesting that the replacement rate of SOD is higher under modern-day conditions than on early Earth. Our data suggest that the early branching cyanobacterium Pseudanabaena sp. PCC7367 may have retained ancestral features permitting it to thrive in its ecological niche as a benthic mat in shallow water marine environments.

microbiology↗

bioRxiv2023

Chloroplasts lacking class I glutaredoxins are functional but show a delayed recovery of protein cysteinyl redox state after oxidative challenge

Redox status of protein cysteinyl residues is mediated via glutathione (GSH)/glutaredoxin (GRX) and thioredoxin (TRX)-dependent redox cascades. An oxidative challenge can induce post-translational protein modifications on thiols, such as protein S-glutathionylation. Class I GRX are small thiol-disulfide oxidoreductases that reversibly catalyse S-glutathionylation and protein disulfide formation. TRX and GSH/GRX redox systems can provide partial backup for each other in several subcellular compartments, but not in the plastid stroma where TRX/light-dependent redox regulation of primary metabolism takes place. While the stromal TRX system has been studied at detail, the role of class I GRX on plastid redox processes in vivo is still unknown. We generate knockout lines of GRXC5 as the only chloroplast class I GRX of the moss Physcomitrium patens. While we find that class I PpGRXC5 has high activities in glutathione-dependent oxidoreductase assays using hydroxyethyl disulfide or redox-sensitive GFP2 (roGFP2) as substrates in vitro, {Delta}grxc5 plants show no detectable growth defect or stress sensitivity, in contrast to mutants with a less negative stromal EGSH ({Delta}gr1). Using stroma-targeted roGFP2, we show increased protein Cys oxidation and decreased reduction rates after oxidative challenge in {Delta}grxc5 plants in vivo, indicating kinetic uncoupling of the protein Cys redox state from glutathione redox potential. Protein Cys disulfide and S-glutathionylation formation rates after H2O2 treatment remained unchanged. Lack of class I GRX function in the stroma did not result in impaired carbon fixation. Our observations suggest specific roles for class I GRX in the efficient redox equilibration between EGSH and protein Cys in the plastid stroma as well as negligible cross-talk with metabolic regulation via the TRX system. We propose a model for stromal class I GRX function as efficient kinetic couplers of protein Cys redox state to the dynamic stromal EGSH and highlight the importance of identifying in vivo target proteins of GRXC5. One sentence summaryRemoval of class I GRX activity in the chloroplast stroma of P. patens kinetically uncouples GRX-dependent cysteine redox changes from the local glutathione redox potential, without an effect on NPQ or photosynthetic carbon reactions.

plant biology↗