The genes coding for the core metabolic enzymes of the photorespiratory pathway that allows plants with C3-type photosynthesis to survive in an oxygen-rich atmosphere, have been largely discovered in genetic screens aimed to isolate mutants that are unviable under ambient air. As an exception, glycolate oxidase (GOX) mutants with a photorespiratory phenotype have not been described yet in C3 species. Using Arabidopsis (Arabidopsis thaliana) mutants lacking the peroxisomal CATALASE2 (cat2-2) that display stunted growth and cell death lesions under ambient air, we isolated a second-site loss-of-function mutation in GLYCOLATE OXIDASE1 (GOX1) that attenuated the photorespiratory phenotype of cat2-2. Interestingly, knocking out the nearly identical GOX2 in the cat2-2 background did not affect the photorespiratory phenotype, indicating that GOX1 and GOX2 play distinct metabolic roles. We further investigated their individual functions in single gox1-1 and gox2-1 mutants and revealed that their phenotypes can be modulated by environmental conditions that increase the metabolic flux through the photorespiratory pathway. High light negatively affected the photosynthetic performance and growth of both gox1-1 and gox2-1 mutants, but the negative consequences of severe photorespiration were more pronounced in the absence of GOX1, which was accompanied with lesser ability to process glycolate. Taken together, our results point toward divergent functions of the two photorespiratory GOX isoforms in Arabidopsis and contribute to a better understanding of the photorespiratory pathway.The increase in atmospheric CO 2 levels linked to global warming, which entails unpredictable climate conditions, poses an unprecedented pressure on modern agriculture (Lobell and Gourdji, 2012; Wheeler and von Braun, 2013). However, apart from its greenhouse properties, CO 2 and its photosynthetic assimilation into biomass are the primary foundation of life on Earth. Thus, atmospheric CO 2 content has a direct effect on agricultural production, and even a modest CO 2 increase might in theory result in higher crop yields, especially in plants with C3-type photosynthesis (Walker et al., 2016). In contrast to C4 and CAM-type plants, C3 plants do not possess carbon concentrating mechanisms, and the first stable CO 2 assimilation product is 3-phosphoglycerate that is further processed in the Calvin-Benson cycle to fuel sugar synthesis. C4 plants initially incorporate CO 2 into four-carbon acids that are subsequently decarboxylated in the vicinity of the primary CO 2 -assimilating enzyme Rubisco. The C4-type photosynthesis evolved independently over 60 times (Sage et al., 2011), reflecting the need to counteract the highly promiscuous nature of Rubisco that apart from carboxylation of ribulose-1,5-bisphosphate also catalyzes its oxygenation to 2-phosphoglycolate (PG). This oxygenation reaction initiates the photorespiratory pathway that recycles PG back to 3-phosphoglycerate with the release of CO 2 in a series of enzymatic steps distributed between chl...

Extracellular vesicles (EVs), e.g., exosomes and microvesicles, are one of the main networks of intercellular communication. In myeloproliferative neoplasms, such as polycythemia vera (PV), excess of EVs originating from overabundant blood cells can directly contribute to thrombosis through their procoagulant activity. However, the proteomic composition of these vesicles in PV patients has not been investigated before. In this work, we examined the proteomic composition of serum EVs of PV patients in comparison to healthy controls. We processed EV-enriched serum samples using the Multiple Enzyme Filter Aided Sample Preparation approach (MED-FASP), conducted LC-MS/MS measurements on a Q-Exactive HF-X mass spectrometer, and quantitatively analyzed the absolute concentrations of identified proteins by the Total Protein Approach (TPA). Thirty-eight proteins were present at statistically significant different concentrations between PV patients’ study group and healthy controls’ group. The main protein components deregulated in PV were primarily related to excessive amounts of cells, increased platelet activation, elevated immune and inflammatory response, and high concentrations of procoagulant and angiogenic agents. Our study provides the first quantitative analysis of the serum EVs’ proteome in PV patients. This new knowledge may contribute to a better understanding of the secondary systemic effects of PV disease and further development of diagnostic or therapeutic procedures.