Biology subjects

Strand, D. D.

Publications and source records attributed to Strand, D. D..

5 recordsLinked to original sources

bioRxiv2025

Native catalase expression in Arabidopsis thaliana is more than sufficient to limit excess decarboxylation from photorespiratory intermediates

The hydrogen peroxide (H2O2) scavenging enzyme, catalase, plays a critical role in the photorespiratory pathway by maintaining the balance of H2O2, a reactive oxygen species (ROS), in the peroxisome. H2O2 acts as both a signaling molecule and a potential source of ROS depending on its accumulation in the peroxisome. Additionally, H2O2 can also drive non-enzymatic decarboxylation (NED) reactions as well as other decarboxylation reactions, leading to increased CO2 release that is linked to a severe growth phenotype. However, the exact cause of this stunted growth phenotype is not fully understood, and it remains unclear whether the capacity of catalase is critical for minimizing these decarboxylating reactions. Here we elucidate the mechanism behind the decrease in plant growth due to the accumulation of H2O2 from photorespiration using cat2 knock-out lines of Arabidopsis thaliana rescued with transgenic expression lines of Heliobacter pylori catalase. These experiments demonstrated that while one of the three heterologous lines expressing H. pylori catalase isoform (Hp615) had greater catalase activity than cat2-KO and rescued the severe growth and photosynthetic phenotype, its catalase activity was still far below wild type levels. These findings suggest that catalase plays a crucial role in maintaining H2O2 homeostasis within the peroxisome and minimizing decarboxylation reactions, both of which are linked to plant growth. Moreover, once a threshold capacity is reached, increasing catalase capacity further may offer limited benefits in enhancing net carbon fixation. HighlightWe show that peroxisomal catalase is important for maintaining high rates of net carbon fixation associated with plant growth. Native catalase levels in Arabidopsis thaliana are in excess of that which is required to minimize alternative decarboxylation reactions. Therefore, efforts to optimize catalase-mediated degradation of H2O2 may be of limited benefit.

plant biology↗

bioRxiv2024

Proton channel inactivation results in loss of chloroplast NDH complex activity

The plastidal photosynthetic complex I (formerly NAD(P)H dehydrogenase-like complex, NDH) remains enigmatic in its function within the electron transport chain of higher plants. While the NDH complex shares high homology with complex I, a key component of the respiratory electron transport chain, electron transport rates through the NDH complex in thylakoids are relatively low. In this study, we took a structure-function approach and mutated the plastid genome-encoded ndhF gene to abolish the NdhF proton channel of the NDH complex. These mutations led to loss of plastoquinone reductase activity, indicating tight coupling between the proton and electron transfer reactions within NDH. Additionally, loss of the transverse helix of NdhF led to loss of the NDH complex, suggesting that this region of the NdhF subunit is required for complex stability. In agreement with previous studies using ndh knockout mutants, loss of NDH complex activity did not result in measurable changes in rates of steady-state cyclic electron flow. However, all mutants displayed a shift in the sensitivity of pH-dependent feedback regulation of the photosystem II antennae to total protonmotive force (pmf), indicating a defect in either stromal redox state or pmf distribution into {Delta}pH and {Delta}{psi}.

biochemistry↗

bioRxiv2022

The K+ exchange antiporter 3 senses the chloroplast energy status to synchronize photosynthesis

Plant photosynthesis contains two functional modules, the light-driven reactions in the thylakoid membrane and the carbon-fixing reactions in the chloroplast stroma. In nature, light availability for photosynthesis often undergoes massive and rapid fluctuations. Efficient and productive use of such variable light supply requires an instant crosstalk and rapid synchronization of both functional modules. Here, we show that this communication involves the stromal exposed regulatory C-terminus (RCT) of the thylakoid K+-exchange antiporter KEA3. RCT-mediated control of KEA3 contributes to the balance between light capture and photoprotection. By combining in silico, in vitro, and in vivo approaches, we demonstrate that the RCT senses the energy state of the chloroplast in form of both, phosphorylation and redox potential, in a pH-dependent manner and regulates KEA3 activity in response. Together our data pinpoint a regulatory feedback loop by which the stromal energy state orchestrates light capture and photoprotection via KEA3.

plant biology↗

bioRxiv2021

Functional characterization of mutants deficient in N-terminal phosphorylation of the CF1 subunit beta

Understanding the regulation of photosynthetic light harvesting and electron transfer is of great importance to efforts to improve the ability of the electron transport chain to supply downstream metabolism. The central regulator of the electron transport chain is the ATP synthase, the molecular motor that harnesses the chemiosmotic potential generated from proton coupled electron transport to synthesize ATP. The ATP synthase is regulated both thermodynamically and post-translationally, with proposed phosphorylation sites on multiple subunits. In this study we focused on two N-terminal serines on the catalytic subunit {beta}, previously proposed to be important for dark inactivation of the complex to avoid ATP hydrolysis at night. Here we show that there is no clear role for phosphorylation in the dark inactivation of ATP synthase. Instead, mutation of one of the two phosphorylated serine residues to aspartate strongly decreased ATP synthase abundance. We propose that the loss of N-terminal phosphorylation of ATP{beta} may be involved in proper ATP synthase accumulation during complex assembly.

plant biology↗

bioRxiv2018

Loss of Peroxisomal Hydroxypyruvate Reductase Inhibits Triose Phosphate Isomerase but Stimulates Cyclic Photosynthetic Electron Flow and the Glc-6P-Phosphate Shunt

The oxygenation of ribulose 1,5-bisphosphate by Rubisco is the first step in photorespiration and reduces the efficiency of photosynthesis in C3 plants. Our recent data indicates that mutants in photorespiration have increased rates of photosynthetic cyclic electron flow around photosystem I. We investigated mutant lines lacking peroxisomal hydroxypyruvate reductase to determine if there are connections between 2-PG accumulation and cyclic electron flow. We found that 2-PG is a competitive inhibitor of triose phosphate isomerase (TPI), an enzyme in the Calvin-Benson cycle that converts glyceraldehyde 3-phosphate to dihydroxyacetone phosphate. This block in metabolism could be overcome if glyceraldehyde 3-phosphate is exported to the cytosol where the cytosolic triose phosphate isomerase could convert it to dihydroxyacetone phosphate. We found evidence that carbon is reimported as Glc-6P-phosphate forming a cytosolic bypass around the block of stromal TPI. However, this also stimulates a Glc-6P-phosphate shunt, which consumes ATP, which can be compensated by higher rates of cyclic electron flow.\n\nOnce Sentence SummaryTriose phosphate isomerase is inhibited in plants lacking hydroxypyruvate reductase 1 and this is overcome by exporting triose phosphate to the cytosol and importing Glc-6P, which stimulates a Glc-6P-phosphate shunt and cyclic electron flow.

plant biology↗