DBG's Eduard Strasburger Workshop - Co- and posttranslational control in chloroplasts

Cyclic electron flow (CEF) in photosynthesis has been studied for decades, yet many aspects of its components, mechanisms, and regulation remain unclear. PROTON GRADIENT REGULATION5 (PGR5) is thought to play a crucial role in promoting CEF. The absence of PGR5 disrupts photosynthetic control and increases the sensitivity of photosystem I (PSI) to light damage, resulting in plant death under...

Post-translational modifications (PTMs) control protein stability, localization, turn-over and interactions, thus represent a fine-tuned regulatory mechanism to reversibly adjust cellular physiology.
In photosynthetic eukaryotes, light-dependent phosphorylation of thylakoid proteins dynamically regulates the light-harvesting apparatus in response to environmental fluctuations. In the...

In this study, we examined plastocyanin (PC) binding and electron transfer with both photosystem I (PSI) and cytochrome b6f (cyt b6f), and show the synergetic adaptations between these three enzymes. Furthermore, we explored the effects of PC phosphorylation on these interactions. To do so, we generated several recombinant variants of PC, in which we genetically engineered two of the...

Fixing CO2 via photosynthesis requires ATP and NADPH. Linear electron transfer (LET) supplies both metabolites, yet depending on environmental conditions, additional ATP is required which can be generated by cyclic electron transfer (CET). Recent studies suggest that CET, which draws electrons from the ferredoxin pool affects the redox regulation of the Calvin-Benson cycle enzymes involved in...

Acetylation is one of the most common chemical modifications affecting a variety of molecules ranging from metabolites to proteins. Recent development of enrichment techniques and mass spectrometry has revealed that acetylation is a prevalent modification also in plants, and that in addition to cytosolic and nuclear proteins also numerous chloroplast proteins are acetylated. We have...

Plants are exposed to a constantly changing environment, which requires fast acclimation strategies. Post-translational modifications (PTMs) of proteins allow cells to respond rapidly to varying environmental conditions and have the potential to alter localization, interactions, or enzymatic activities of proteins. Protein acetylation is one of the most abundant co- and post-translational...

The photosystem II (PSII) supercomplex (SC) of higher plants is a (multi)protein-pigment assembly performing the initial steps of photosynthetic electron transport consisting of water oxidation and photochemical plastoquinone reduction. In angiosperms, the PSII SC is equipped with three LHCB4-6 monomeric pigment-binding proteins which connect the dimeric core complex with the peripheral...

In plant chloroplasts, protein kinases regulate photosynthetic acclimation by phosphorylation of thylakoid membrane proteins allowing rapid short-term acclimation to changing light conditions. This type of phosphorylation control is mediated by the light-regulated kinases STN7/STN8 at the thylakoid membrane system. Recent data suggested furthermore that STN7 may be involved in long-term...

Regulation of Rubisco activity by light in tomato
Joana Amaral, Dawn Worrall, Elizabete Carmo-Silva
Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK

Rubisco is the most abundant protein in the chloroplast, fixing CO₂ into sugars during photosynthesis. Its activity is finely adjusted in response to changes in the environment. The regulation of Rubisco by...

Most plant cell compartments possess oxidoreductases that catalyze the interconversion between malate and oxaloacetate (OAA) in a reversible reaction. These malate dehydrogenases (MDHs) are either NAD- or NADP-specific.
Together with malate/OAA translocators, MDHs enable the indirect exchange of reducing equivalents across subcellular membranes. The exported malate can then be used as a...

Tetrapyrrole biosynthesis (TPB) in plants consists of more than twenty enzymatic steps and is tightly controlled due to the synthesis of photoreactive intermediates and the different spatial and temporal requirements of their end products chlorophyll and heme. At the TPB hotspots, many complementary post-translational control mechanisms act on specific enzymes: The two enzymes glutamyl-tRNA...

The pyrimidine nucleotide cofactors NAD and NADP operate at the critical intersection between the cellular metabolic network, Cys-based systems and redox regulation. In plants, the redox states of the NAD and NADP pools of the cytosol and the chloroplast stroma are physically separated, but connected by metabolic shuttles, such as the malate/oxaloacetate and the triose-phosphate shuttle....

Plants undergo daily dark-light transitions, leading to dynamic changes of the metabolic and physiological status of their cells. Those changes, which include cofactors, ions and other small molecules such as ATP, NAD(P) redox status, ROS, Ca2+ and pH, are a prerequisite for tuning protein functions through post-translational modifications (PTMs). However, it has been notoriously difficult to...

Arabidopsis plants can produce photosynthetic tissue with active chloroplasts at temperatures as low as 4°C, and this process depends on the presence of the nuclear-encoded, chloroplast-localized RNA-binding protein CP29A. We demonstrate that CP29A undergoes phase separation in vitro and in vivo in a temperature-dependent manner, which is mediated by a prion-like domain (PLD) located between...

ABSTRACT Different proteases and peptidases are present within chloroplasts and non-photosynthetic plastids to process precursor proteins and to degrade cleaved chloroplast transit peptides and damaged, misfolded, or otherwise unwanted proteins. Collectively, these proteases and peptidases form a proteolysis network, with complementary activities and hierarchies, and build-in redundancies [1]....

In plant chloroplasts, protein kinases regulate photosynthetic acclimation by phosphorylation of thylakoid membrane proteins allowing rapid short-term acclimation to changing light conditions. This type of phosphorylation control is mediated by the light-regulated kinases STN7/STN8 at the thylakoid membrane system. Recent data suggested furthermore that STN7 may be involved in long-term...