Stress-related expression of the chloroplast EGY3 pseudoprotease and its possible impact on chloroplasts’ proteome composition

Abstract

The EGY3 is a pseudoprotease, located in the thylakoid membrane, that shares homology with the family of site-2-proteases (S2P). Although S2P proteases are present in the cells of all living organisms, the EGY3 was found only in plant cells. The sequence of the pseudoprotease is highly conserved in the plant kingdom; however, little is known about its physiological importance. Results obtained with real-time PCR indicated that the expression of the EGY3 gene is dramatically induced during the first few hours of exposure to high light and high-temperature stress. The observed increase in transcript abundance correlates with protein accumulation level, which indicates that EGY3 participates in response to both high-temperature and high light stresses. The lack of the pseudoprotease leads, in both stresses, to lower concentrations of hydrogen peroxide. However, the decrease of chloroplast copper/zinc superoxide dismutase 2 level was observed only during the high light stress. In both analyzed stressful conditions, proteins related to RubisCO folding, glycine metabolism, and photosystem I were identified as differently accumulating in egy3 mutant lines and WT plants; however, the functional status of PSII during analyzed stressful conditions remains very similar. Our results lead to a conclusion that EGY3 pseudoprotease participates in response to high light and high-temperature stress; however, its role is associated rather with photosystem I and light-independent reactions of photosynthesis.

Exploring Aluminum Tolerance Mechanisms in Crops: A Comprehensive Review of Genetic, Metabolic, and Physiological Adaptations in Acidic Soils

“…Various ROS forms are generated, including singlet oxygen, superoxide, hydrogen peroxide and, hydroxyl radicals. The uptake of Al 3+ induces the expression of certain genes in the chloroplast genomewhich includes membrane-bound ATP-independent proteases that play a significant role in Al tolerance mechanisms [32]. The mechanisms of Al tolerance are complex, involving the synergistic contributions of metal compartmentalization, chloroplast fluorescence, mitochondrial oxidative reactions, and peroxisomal carbon oxidation (Figure 2).…”

S2P2—the chloroplast-located intramembrane protease and its impact on the stoichiometry and functioning of the photosynthetic apparatus of A. thaliana

“…Except for the product of the At4g20310 gene, the remaining proteins are located within chloroplasts. Much is already known about the significance and possible functions of EGY1 (e.g., Chen et al, 2005Chen et al, , 2016Yu et al, 2016;Qi et al, 2020;Adamiec et al, 2021a;Adamiec et al, 2021b) and EGY2 proteases (Chen et al, 2012;Adamiec et al, 2018;Luciński et al, 2024), as well as EGY3, which, due to the lack of the characteristic zinc-binding motif (HExxH), lacks proteolytic activity and is classified as a so-called pseudoprotease (Adamiec et al, 2020(Adamiec et al, , 2022. However, knowledge about the physiological functions of S2P2 is extremely limited.…”

“…The lack of these proteases is also associated with increased sensitivity of plants to photoinhibition (Adamiec et al, 2018, 2021a, Luciński et al, 2024. The latter effect is also observed in the absence of the EGY3 pseudoprotease (Adamiec et al, 2020), the absence of which is also associated with increased production of reactive oxygen species by chloroplasts of plants exposed to the stress of high temperature and high light intensity (Adamiec et al, 2022).…”

Protein-protein interactions in plant antioxidant defense

“…These proteases occur in prokaryotes, mammals and plants, however, EGY3 was identified only in plants with high conservation in the plant kingdom ( Adamiec et al., 2017 ; Adamiec et al., 2020 ). EGY3 expression is strongly induced by salt, oxidative stress ( Zhuang et al., 2021 ), high light, and high temperature stress ( Adamiec et al., 2022 ). The stress-induced interaction of CSD2 with M50-like domain of EGY3 stabilizes CSD2 as indicated by decreased abundance of CSD2 under salt stress and high light conditions in egy3 mutants.…”

“…The stress-induced interaction of CSD2 with M50-like domain of EGY3 stabilizes CSD2 as indicated by decreased abundance of CSD2 under salt stress and high light conditions in egy3 mutants. The CSD2-EGY3 interaction is important for H 2 O 2 pool maintenance to ensure chloroplast-nucleus retrograde signaling ( Zhuang et al., 2021 ; Adamiec et al., 2022 ). The Cu 2+ -dependence of this regulation remains to be revealed.…”