Biology subjects

Pfannschmidt, T.

Publications and source records attributed to Pfannschmidt, T..

4 recordsLinked to original sources

bioRxiv2023

Photosynthesis in the biomass model species Lemna minor displays plant-conserved and species-specific features

Lemnaceae are aquatic freshwater plants with extraordinary high growth rates. We have studied selected physiological and molecular photosynthesis properties of the duckweed Lemna minor and compared these to the terrestrial model species Arabidopsis thaliana. Lemna and Arabidopsis plants grown under identical light intensities displayed similar photosynthesis characteristics, however, Lemna exhibited slighty better quenching efficiencies pointing to improved light utilization in the duckweed. Western-immuno-blot analyses of representative photosynthesis proteins suggest various post-translational modifications in Lemna that might be associated to this. Phospho-threonine phosphorylation patterns of thylakoid membranes uncovered differences between the two species. Testing the photosystem II antenna association of Lemna minor in dark and light by 77K chlorophyll fluorescence emission experiments, however, revealed a typical association as reported in terrestrial plants. High light stress experiments causing photoinhibition and subsequent recovery from it were not substantially different in Lemna when compared to Arabidopsis. We hypothesize that the molecular differences in Lemna photosynthesis proteins are associated with evolutionary adaptations to the aquatic life style and ultimately with the high growth rates. We also developed a video imaging approach for Lemna multiplication at high magnification that will be useful to assess the impact of external factors on Lemna photosynthesis and growth.

plant biology↗

bioRxiv2022

Limiting etioplast gene-expression induces apical hook twisting during skoto-morphogenesis of Arabidopsis seedlings

When covered by a layer of soil, seedling development follows a dark-specific program (skoto-morphogenesis) consisting of small, non-green cotyledons, a long hypocotyl and an apical hook to protect meristematic cells. We recently highlighted the role played by mitochondria in the high energy-consuming reprogramming of Arabidopsis skoto-morphogenesis. Here, the role played by plastids, another energy supplying organelle, in skoto-morphogenesis is investigated. This study was conducted in dark conditions to exclude light signals so as to better focus on those produced by plastids. It was found that limitation of plastid gene-expression (PGE) induced an exaggerated apical hook bending. Inhibition of PGE was obtained at the level of transcription and translation using the antibiotics rifampicin and spectinomycin, respectively, as well as plastid RPOTP RNA polymerase mutants. Rifampicin-treated seedlings also showed expression induction of marker nuclear genes for mitochondrial stress, perturbation of the mitochondrial metabolism, increase of ROS levels and an augmented capacity of oxygen consumption by mitochondrial alternative oxidases (AOX). AOX enzymes act to prevent over-reduction of the mitochondrial electron transport chain. Previously, we reported that AOX1A, the main AOX isoform, was a key component in the developmental response to mitochondrial respiration deficiency. In this work, we suggest the involvement of AOX1A in the response to PGE dysfunction and propose the importance of signalling between plastids and mitochondria. Finally, it was found that seedling architecture reprogramming in response to rifampicin was independent of canonical organelle retrograde pathways and the ethylene signaling pathway. Significance statementIn underground germination conditions, seedling development follows a dark-specific program (skoto-morphogenesis) consisting of small and non-green cotyledons, a long hypocotyl and an apical hook to protect meristematic cells. We show that skoto-morphogenesis is reprogrammed when plastid gene expression is perturbed leading to an exaggeration of apical hook bending. We propose the involvement of the cooperation between plastids and mitochondria, the energy-supplying organelles of the cell.

plant biology↗

bioRxiv2022

Three-dimensional envelope and subunit interactions of the plastid-encoded RNA polymerase from Sinapis alba

RNA polymerases (RNAPs) involved in gene transcription are found in all living organisms with degrees of complexity ranging from single polypeptide chains to multimeric enzymes. In the chloroplasts, the nuclear-encoded RNA polymerase and the plastid-encoded RNA polymerase (PEP) are both involved in the selective transcription of the plastid genome. The PEP is a prokaryotic-type multimeric RNAP found in different states depending on light stimuli and cell identity. One of its active states requires the assembly of nuclear-encoded PEP-Associated Proteins (PAPs) on the catalytic core, producing a complex of more than 900 kDa regarded as essential for chloroplast biogenesis. A purification procedure compatible with structural analysis was used to enrich the native PEP from Sinapis alba chloroplasts. Mass spectrometry (MS)-based proteomic analysis identified the core components, the PAPs and additional members, and coupled to cross-linking (XL-MS) provided initial structural information about the relative position of PEP subunits. Sequence alignments of the catalytic core subunits across various chloroplasts of the green lineage and prokaryotes combined with structural data show that the overall shape of the catalytic core and the residues essential for the catalytic activity are conserved. However, variations are observed at the surface of the core, some of them corresponding to PAP binding sites as suggested by XL-MS experiments. Using negative stain electron microscopy, the PEP 3D envelope was calculated. 3D classification shows that the protrusions which we attribute to the PAPs are firmly associated with the catalytic core. Overall, the shape of the S. alba PEP envelope is different from that of RNAPs.

biochemistry↗

bioRxiv2020

Nucleo-plastidic PAP8/pTAC6 couples chloroplast formation with photomorphogenesis

The initial greening of angiosperm occurs upon light-activation of photoreceptors that trigger photomorphogenesis followed with the development of chloroplasts. In these semi-autonomous organelles, the construction of the photosynthetic apparatus depends on the coordination of nuclear and plastid gene expression. Here we show that PAP8, as an essential subunit of the plastid-encoded RNA polymerase, is under the control of a regulatory element recognized by the photomorphogenic factor HY5. PAP8 is localized and active in both plastids and the nucleus and particularly essential for the formation of late photobodies. In the albino pap8 mutant, phytochrome-mediated signalling is altered, PIFs are maintained, HY5 is not stabilized, and GLK1 expression is impaired. PAP8 translocates into plastids losing its pre-sequence, interacts with the PEP, and using an unknown route or a retrograde transport, reaches the nucleus where it has the ability to interact with pTAC12/HMR/PAP5. Since PAP8 is required for the phytochrome-B-mediated signalling cascade and the reshaping of the PEP, it may coordinate nuclear gene expression with the PEP-driven chloroplastic gene expression during chloroplast biogenesis.

plant biology↗