Biology subjects

Baginsky, S.

Publications and source records attributed to Baginsky, S..

5 recordsLinked to original sources

bioRxiv2026

Tvp38/DedA Family Protein mediates biogenesis of chloroplast peripheral reticulum and envelope-to-thylakoid contacts in Arabidopsis

Chloroplasts of land plants are dynamic organelles essential for photosynthesis, metabolism, and plant adaptation to changing environmental conditions. Within chloroplasts, the inner envelope and thylakoid membranes are spatially separated but functionally interconnected. The inner envelope harbors enzymes involved in lipid synthesis for internal membranes and controls the exchange of metabolites and proteins, whereas the thylakoid membranes accommodate the machinery of the photosynthetic electron transport chain responsible for converting light energy into chemical energy. Therefore, efficient communication between these membrane systems is essential for maintaining chloroplast homeostasis and sustaining photosynthetic activity. In this study we have characterized the role of Tvp38/DedA Family Protein (TVPFP) in mediating inner envelope-to-thylakoid communication in Arabidopsis thaliana. Despite exhibiting wild-type-like growth and similar accumulation of the major thylakoid-anchored photosynthetic complexes, tvpfp mutants displayed reduced photosynthetic activity and increased abundance of photorespiration- and pigment-related proteins. Our results revealed that TVPFP localizes to the chloroplast envelope and undergoes post-translational modification when localized to the thylakoids. The unmodified form of TVPFP is enriched in high-molecular-weight complexes, suggesting that TVPFP oligomers are partially dissolved upon thylakoid relocation. Transmission electron microscopy data showed reduced abundance of vesicles as well as chloroplast peripheral reticulum (CPR) structures connecting the envelope and thylakoids in tvpfp mutants. Together, our results demonstrate that TVPFP fine-tunes photosynthesis by regulating vesicle abundance and biogenesis of CPR structures. Our findings shed light on the importance of envelope-to-thylakoid communication and the role of CPR structures in land plants.

plant biology↗

bioRxiv2026

Phenotypic characterization of an Arabidopsis stn7 stn8 pck2 triple mutant reveals only minor effects on chloroplast functions

Reversible protein phosphorylation is a key regulator of chloroplast function. Although chloroplast kinases STN7, STN8, and plastid casein kinase 2 (pCK2) regulate photosynthetic acclimation and other chloroplast processes, their functional interplay remains poorly understood. We generated and characterized the first Arabidopsis thaliana stn7 stn8 pck2 triple knockout mutant. Biochemical analyses confirmed the loss of all three kinase activities on established substrates. Growth resembled the pck2 single mutant, whereas photosynthetic fluorescence parameters reflected the stn7 stn8 double mutant. Thus, simultaneous disruption of all three kinases primarily combined the parental phenotypes, with little evidence of additive or synergistic effects under standard growth conditions. This triple mutant enables studies of chloroplast phosphorylation networks and demonstrates the remarkable resilience of chloroplast physiology to combined kinase loss.

plant biology↗

bioRxiv2022

Proteomic identification of the interactome of stalled ribosome nascent chain complexes translating the thylakoid membrane protein D1

The synthesis of multi-span thylakoid membrane proteins initiates at ribosomes off the membrane. Subsequently, the ribosome nascent chain complexes (RNCs) are transferred to the translocase machinery in the thylakoid membrane for cotranslational protein insertion. These steps require finely tuned mechanisms for protein processing, quality control, and targeting to prevent misfolding or aggregation and to ensure efficient transfer of the nascent chain to the insertion machinery. However, little is known about the regulatory network underlying these processes. To identify factors specifically involved in the cotranslational biogenesis of the reaction center protein D1 of photosystem II we established a chloroplast-derived in vitro translation method that allows the production and affinity purification of stalled RNCs bearing nascent chains of D1 of different defined lengths. Stalled RNCs translating the soluble ribosomal subunit uS2c were affinity-purified for comparison. Quantitative tandem-mass spectrometry revealed a set of about 120 proteins specifically associated with D1 RNCs. The interactome includes proteins with broad functions in protein processing, biogenesis and metabolic pathways, such as chlorophyll biosynthesis. We identified STIC2 as a new factor specifically associated with D1 RNCs. Furthermore, our results demonstrated that the interaction of STIC2 with the thylakoid insertase Alb3 and its homologue Alb4 is mediated by the conserved motif III within the C-terminal regions of Alb3 and Alb4. Our data suggest that STIC2 is involved in cotranslational substrate delivery at the thylakoid membrane by coordinating the binding of the D1 RNCs to the insertase machinery.

plant biology↗

bioRxiv2020

Chromoplast differentiation in bell pepper (Capsicum annuum) fruits

We report here a detailed analysis of the proteome adjustments that accompany chromoplast differentiation from chloroplasts during bell-pepper fruit ripening. While the two photosystems are disassembled and their constituents degraded, the cytochrome b6f complex, the ATPase complex as well as Calvin cycle enzymes are maintained at high levels up to fully mature chromoplasts. This is also true for ferredoxin (Fd) and Fd-dependent NADP reductase, suggesting that ferredoxin retains a central role in the chromoplasts redox metabolism. There is a significant increase in the amount of enzymes of the typical metabolism of heterotrophic plastids such as the oxidative pentose phosphate pathway (OPPP), amino acid and fatty acid biosynthesis. Enzymes of chlorophyll catabolism and carotenoid biosynthesis increase in abundance, supporting the pigment reorganization that goes together with chromoplast differentiation. The majority of plastid encoded proteins declines but constituents of the plastid ribosome and AccD increase in abundance. Furthermore, the amount of plastid terminal oxidase (PTOX) remains unchanged despite a significant increase in phytoene desaturase (PDS) levels, suggesting that the electrons from phytoene desaturation may be consumed by another oxidase. This may be a particularity of non-climacteric fruits such as bell pepper, that lack a respiratory burst at the onset of fruit ripening.

plant biology↗

bioRxiv2020

The Arabidopsis NOT4A E3 ligase coordinates PGR3 expression to regulate chloroplast protein translation

Chloroplast function requires the coordinated action of nuclear- and chloroplast-derived proteins, including several hundred nuclear-encoded pentatricopeptide repeat (PPR) proteins that regulate plastid mRNA metabolism. Despite their large number and importance, regulatory mechanisms controlling PPR expression are poorly understood. Here we show that the Arabidopsis NOT4A ubiquitin-ligase positively regulates PROTON GRADIENT 3 (PGR3), a PPR protein required for translating 30S ribosome subunits and several thylakoid-localised photosynthetic components within chloroplasts. Loss of NOT4A function leads to a strong depletion of plastid ribosomes, which reduces mRNA translation and negatively impacts photosynthetic capacity, causing pale-yellow and slow-growth phenotypes. Quantitative transcriptome and proteome analyses reveal that these defects are due to a lack of PGR3 expression in not4a, and we show that normal plastid function is restored through transgenic PGR3 expression. Our work identifies NOT4A as crucial for ensuring robust photosynthetic function during development and stress-response, through modulating PGR3 levels to coordinate chloroplast protein synthesis.

plant biology↗