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3. Redox regulation in chloroplast thylakoid lumen: The pmf changes everything, again.

Author

Hoh, Donghee, Froehlich, John E., and Kramer, David M.

Subjects
*CHLOROPLASTS, *ENZYME stability, *OXIDATION-reduction reaction, *PROTEIN stability, *REACTIVE oxygen species, *SULFHYDRYL group
Abstract

Photosynthesis is the foundation of life on Earth. However, if not well regulated, it can also generate excessive reactive oxygen species (ROS), which can cause photodamage. Regulation of photosynthesis is highly dynamic, responding to both environmental and metabolic cues, and occurs at many levels, from light capture to energy storage and metabolic processes. One general mechanism of regulation involves the reversible oxidation and reduction of protein thiol groups, which can affect the activity of enzymes and the stability of proteins. Such redox regulation has been well studied in stromal enzymes, but more recently, evidence has emerged of redox control of thylakoid lumenal enzymes. This review/hypothesis paper summarizes the latest research and discusses several open questions and challenges to achieving effective redox control in the lumen, focusing on the distinct environments and regulatory components of the thylakoid lumen, including the need to transport electrons across the thylakoid membrane, the effects of pH changes by the proton motive force (pmf) in the stromal and lumenal compartments, and the observed differences in redox states. These constraints suggest that activated oxygen species are likely to be major regulatory contributors to lumenal thiol redox regulation, with key components and processes yet to be discovered. [ABSTRACT FROM AUTHOR]

Published
2024
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18. Chloroplast phosphatases LPPγ and LPPε1 facilitate conversion of extraplastidic phospholipids to galactolipids.

Author

Cook, Ron, Froehlich, John E, Yang, Yang, Korkmaz, Ilayda, Kramer, David M, and Benning, Christoph

Abstract

Galactolipids comprise the majority of chloroplast membranes in plants, and their biosynthesis requires dephosphorylation of phosphatidic acid at the chloroplast envelope membranes. In Arabidopsis (Arabidopsis thaliana), the lipid phosphate phosphatases LPPγ, LPPε1, and LPPε2 have been previously implicated in chloroplast lipid assembly, with LPPγ being essential, as null mutants were reported to exhibit embryo lethality. Here, we show that lppγ mutants are in fact viable and that LPPγ, LPPε1, and LPPε2 do not appear to have central roles in the plastid pathway of membrane lipid biosynthesis. Redundant LPPγ and LPPε1 activity at the outer envelope membrane is important for plant development, and the respective lppγ lppε1 double mutant exhibits reduced flux through the ER pathway of galactolipid synthesis. While LPPε2 is imported and associated with interior chloroplast membranes, its role remains elusive and does not include basal nor phosphate limitation-induced biosynthesis of glycolipids. The specific physiological roles of LPPγ, LPPε1, and LPPε2 are yet to be uncovered, as does the identity of the phosphatidic acid phosphatase required for plastid galactolipid biosynthesis. Chloroplast lipid phosphatases LPPγ and LPPε1 have redundant activity in facilitating conversion of extraplastidic phosphatidic acid to galactolipids and are important for plant growth. [ABSTRACT FROM AUTHOR]

Published
2024
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