Biology subjects

Schöttler, M. A.

Publications and source records attributed to Schöttler, M. A..

4 recordsLinked to original sources

bioRxiv2023

A congestion downstream of PSI causes the over-reduction of the electron transport chain in pgr5 independent of membrane energization

The thylakoid protein Proton Gradient Regulation5 (PGR5) is thought to be a key component of cyclic electron flux around photosystem I. The pgr5 mutant is characterized by impaired proton motive force (pmf) formation across the thylakoid membrane, decreased photoprotective non-photochemical quenching (NPQ), and an over-reduction of the PSI acceptor side. This over-reduction has been attributed to impaired photosynthetic control, which down-regulates plastoquinol re-oxidation at the cytochrome b6f complex when the lumen is strongly acidified. Here, using the cgl160 ATP synthase assembly mutant, we show that in cgl160 pgr5 double mutants, both the pmf across the thylakoid membrane and NPQ are fully restored to wild-type levels. However, the acceptor-side limitation of PSI in the double mutants stays comparable to the single pgr5 mutant. This demonstrates that impaired photosynthetic control is not causal for the over-reduction of the PSI acceptor side in pgr5. Instead, we show that both in pgr5 and the clg160 pgr5 mutants, the entire high-potential chain from cytochrome f to PSI remains strongly reduced in high light. This leads to insufficient oxidizing power for plastoquinol re-oxidation by the cytochrome b6f complex, thus impairing pmf formation. We conclude that PGR5 plays a critical role in electron partitioning downstream of PSI.

plant biology↗

bioRxiv2023

A eukaryote-specific factor mediates an early step in the assembly of plant photosystem II

ABSTRACTThe initial step of oxygenic photosynthesis is the thermodynamically challenging extraction of electrons from water and the release of molecular oxygen. This light-driven process, which is the basis of life on Earth, is catalyzed by the photosystem II (PSII) within the thylakoid membrane of photosynthetic organisms. The biogenesis of PSII requires a controlled step-wise assembly process of which the early steps are considered to be highly conserved between plants and their cyanobacterial progenitors. This assembly process involves auxiliary proteins, which are likewise conserved. In the present work, we show that in plants, the early assembly step, in which the PSII reaction center (RC) is associated with the intrinsic antenna protein CP47 to form the RC47 intermediate, is facilitated by a novel eukaryote-exclusive assembly factor. This factor, we named DEAP2 for DECREASED ELECTRON TRANSPORT AT PSII, works in concert with the conserved PAM68 assembly factor. The deap2 and pam68 mutants showed similar defects in PSII accumulation and assembly of the RC47 intermediate. The combined lack of both proteins results in a loss of functional PSII and the inability of plants to grow photoautotrophically on soil. While overexpression of DEAP2 partially rescued the pam68 PSII accumulation phenotype, this effect was not reciprocal. DEAP2 accumulates at 20-fold higher levels than PAM68, together suggesting that both proteins have distinct functions. In summary, our results uncover eukaryotic adjustments to the PSII assembly process, which involve the addition of DEAP2 for the rapid progression from RC to RC47.

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↗

bioRxiv2020

Correction of frameshift mutations in the atpB gene by translational recoding in chloroplasts of Oenothera and tobacco.

Translational recoding, also known as ribosomal frameshifting, is a process that causes ribosome slippage along the messenger RNA, thereby changing the amino acid sequence of the synthesized protein. Whether the chloroplast employs recoding, is unknown. I-iota, a plastome mutant of Oenothera (evening primrose), carries a single adenine insertion in an oligoA stretch of atpB (encoding a {beta}-subunit of the ATP synthase). The mutation is expected to cause synthesis of a truncated, non-functional protein. We report that a full-length AtpB protein is detectable in I-iota leaves, suggesting operation of a recoding mechanism. To characterize the phenomenon, transplastomic tobacco lines were generated, in which the atpB reading frame was altered by insertions or deletions in the oligoA motif. We found that insertion of two adenines was more efficiently compensated than insertion of a single adenine, or deletion of one or two adenines. We further show that homopolymeric composition of the oligoA stretch is essential for recoding. Plants carrying a disrupted oligoA stretch have an albino-phenotype, indicating absence of indel correction. Our work provides evidence for the operation of translational recoding in chloroplasts. Recoding enables correction of frameshift mutations and can restore photoautotrophic growth in mutants that otherwise would be lethal.

plant biology↗