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In this lecture the main sites of regulation of photosynthetic electron transport will be introduced with a special focus on the plastid terminal oxidase (PTOX). PTOX is a plastohydroquinone:oxygen oxidoreductase that belongs to the non-heme diiron carboxylate family. PTOX is important for carotenoid biosynthesis and plastid development. Its role in photosynthesis is controversially discussed. Under a number of abiotic stress conditions, the expression and the protein level of PTOX increase. PTOX is thought to act as a safety valve under abiotic stress protecting the photosynthetic apparatus against photodamage. However, tobacco transformants with high C. reinhardtii PTOX levels were reported to suffer from chronic photoinhibition. Data will be presented showing that in the transformants PTOX is highly active and competing with photosynthetic electron transport. Confocal microscopy images suggest the localization of PTOX inside the chloroplast depends on the physiological condition. We propose that PTOX activity is regulated via its subcellular localization and its pH-dependent association with the thylakoid membrane. 

References

> Yu Q, Feilke K, Krieger-Liszkay A, Beyer P. (2014) Functional and molecular characterization of plastid terminal oxidase from rice (Oryza sativa). Biochim Biophys Acta 1837,1284-92
> Feilke K, Streb P, Cornic G, Perreau F, Kruk J, Krieger-Liszkay A (2015a) Effect of chlamydomonas plastid terminal oxidase 1 expressed in tobacco on photosynthetic electron transport. Plant. J. 85:219-28.
> Krieger-Liszkay A, Feilke K (2015b) The dual role of the plastid terminal oxidase PTOX: between a protective and a pro-oxidant function. Frontiers in Plant Science 6:1147.
> Bolte S, Marcon E, Jaunario M, Moyet L, Paternostre M, Kuntz M, Krieger-Liszkay A (2020) Dynamics of the localization of the plastid terminal oxidase inside the chloroplast. J Exp Bot.71(9):2661-2669.doi:10.3389/fpls.2015.01147
> Messant M, Shimakawa G, Perreau F, Miyake C, Krieger-Liszkay A. (2021) Biochim Biophys Acta Bioenerg. 1862(1):148309. doi: 10.1016/j.bbabio.2020.148309.