Giese, J. | Search bioRxiv

bioRxiv2020

Photosynthetic activity triggers pH and NAD redox signatures across different plant cell compartments

A characteristic feature of most plants is their ability to perform photosynthesis, which ultimately provides energy and organic substrates to most life. Photosynthesis dominates chloroplast physiology but represents only a fraction of the tightly interconnected metabolic network that spans the entire cell. Here, we explore how photosynthetic activity affects the energy physiological status in cell compartments beyond the chloroplast. We develop precision live monitoring of subcellular energy physiology under illumination to investigate pH, MgATP2- and NADH/NAD+ dynamics at dark-light transitions by confocal imaging of genetically encoded fluorescent protein biosensors in Arabidopsis leaf mesophyll. We resolve the in vivo signature of stromal alkalinisation resulting from photosynthetic proton pumping and observe a similar pH signature also in the cytosol and the mitochondria suggesting that photosynthesis triggers an alkalinisation wave that affects the pH landscape of large parts of the cell. MgATP2- increases in the stroma at illumination, but no major effects on MgATP2- concentrations in the cytosol were resolved. Photosynthetic activity triggers a signature of substantial NAD reduction in the cytosol that is driven by photosynthesis-derived electron export. Strikingly, cytosolic NAD redox status was deregulated in mutants of chloroplastic NADP- and mitochondrial NAD-dependent malate dehydrogenases even at darkness, pinpointing the participation of the chloroplasts and mitochondria in shaping cytosolic redox metabolism in vivo with a dominant function of malate metabolism. Our data illustrate how profoundly and rapidly changes in photosynthetic activity affect the physiological and metabolic landscape throughout green plant cells. One-sentence summaryDark-light transitions trigger profound re-orchestration of subcellular pH and NAD redox physiology not only in the chloroplast but also beyond, in the cytosol and the mitochondria, as revealed by precision live-monitoring using fluorescent protein biosensors.

plant biology↗

bioRxiv2020

An evolutionary conserved lysine acetylation hotspot regulates plant mitochondrial malate dehydrogenase activity

Plants need to rapidly and flexibly adjust their metabolism to changes of their immediate environment. Since this necessity results from the sessile lifestyle of land plants, key mechanisms for orchestrating central metabolic acclimation are likely to have evolved early. Here, we explore the role of lysine acetylation as a posttranslational modification to directly modulate metabolic function. We generated a lysine acetylome of the moss Physcomitrium patens and identified 638 lysine acetylation sites, mostly found in mitochondrial and plastidial proteins. A comparison with available angiosperm data pinpointed lysine acetylation as a conserved regulatory strategy in land plants. Focusing on mitochondrial central metabolism, we functionally analyzed acetylation of malate dehydrogenase (mMDH), which acts as a hub of plant metabolic flexibility. In P. patens mMDH1, we detected a single acetylated lysine located next to one of the four acetylation sites detected in Arabidopsis thaliana mMDH1. We assessed the kinetic behavior of recombinant A. thaliana and P. patens mMDH1 with site-specifically incorporated acetyl-lysines. Acetylation of A. thaliana mMDH1 at K169, K170, and K334 decreases its oxaloacetate reduction activity, while acetylation of P. patens mMDH1 at K172 increases this activity. We found modulation of the malate oxidation activity only in A. thaliana mMDH1, where acetylation of K334 highly activated it. Comparative homology modelling of MDH proteins revealed that evolutionarily conserved lysines serve as hotspots of acetylation. Our combined analyses indicate lysine acetylation as a common strategy to fine-tune the activity of central metabolic enzymes with likely impact on plant acclimation capacity. Significance statementWe explore the role of lysine acetylation as a mechanism to directly modulate mitochondrial metabolism in land plants by generating the lysine acetylome of the moss Physcomitrium patens and comparing with available angiosperm data. We found acetylation of evolutionarily conserved lysines as a strategy to fine-tune the activity of mitochondrial malate dehydrogenase in a species-dependent molecular context.

plant biology↗