Towards understanding of photoacclimation in algal photosynthesis – regulation via redox and Ca2+

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• Michael Hippler, University of Munster
• Thursday 14 December 2017, 13:00-14:00
• Department of Plant Sciences, Large Lecture Theatre.

If you have a question about this talk, please contact david baulcombe.

Photosynthetic organisms must acclimate to their light environment to optimize photosynthesis and minimize photo-oxidative damage. In plants, qE, a component of non-photochemical quenching (NPQ), is required for thermal dissipation of excess absorbed light energy. In C. reinhardtii, LHCSR3 was shown to be crucial for functional qE (Peers et al, 2009). Increased cyclic electron flow (CEF) around PS I is known to promote qE induction by formation of a trans-thylakoid proton gradient. Functional CEF depends on a reorganization of the major protein complexes in the thylakoid membrane, leading to the formation of a PS I -cytochrome b6f supercomplex (CEF-supercomplex) (Iwai et al, 2010; Terashima et al, 2012). There is evidence that that the chloroplast localized Ca2+ sensor protein (CAS) is crucial for effective photo-acclimation in C. reinhardtii by controlling the expression of LHCSR3 (Petroutsos et al, 2011) and required for expression of proteins essential for the carbon-concentrating mechanism (CCM) (Wang et al, 2016). Moreover CAS and Ca2+ are involved in regulation of CEF . Ca2+-dependent regulation of CEF was shown via a combined function of ANR1 and CAS , associated with each other in the CEF -supercomplex (Terashima et al, 2012). Further evidence for the importance of Ca2+ in the regulation of photosynthesis is given by the identification (Hohner et al, 2013) and characterization of a C. reinhardtii protein, which combines four EF-hands and a thioredoxin domain, designated as calredoxin (CRX). Functional data demonstrate that recombinant CRX possesses Ca2+-dependent thioredoxin activity, thereby linking Ca2+ with redox regulation (Hochmal et al, 2016). Down-regulation of calredoxin expression resulted in increased CEF , high ROS and elevated conductivity of the ATPase as well as in a strong repression of highlight-induced proteins, including CCM -induced proteins, a phenotype similar to a CAS -deficient mutant, suggesting a link between CAS and CRX .

References

Hochmal AK, Zinzius K, Charoenwattanasatien R, Gabelein P, Mutoh R, Tanaka H, Schulze S, Liu G, Scholz M, Nordhues A, Offenborn JN, Petroutsos D, Finazzi G, Fufezan C, Huang K, Kurisu G, Hippler M (2016) Calredoxin represents a novel type of calcium-dependent sensor-responder connected to redox regulation in the chloroplast. Nat Commun 7: 11847

Hohner R, Barth J, Magneschi L, Jaeger D, Niehues A, Bald T, Grossman A, Fufezan C, Hippler M (2013) The metabolic status drives acclimation of iron deficiency responses in Chlamydomonas reinhardtii as revealed by proteomics based hierarchical clustering and reverse genetics. Molecular & cellular proteomics : MCP 12 : 2774-2790

Iwai M, Takizawa K, Tokutsu R, Okamuro A, Takahashi Y, Minagawa J (2010) Isolation of the elusive supercomplex that drives cyclic electron flow in photosynthesis. Nature 464: 1210-1213

Peers G, Truong TB, Ostendorf E, Busch A, Elrad D, Grossman AR, Hippler M, Niyogi KK (2009) An ancient light-harvesting protein is critical for the regulation of algal photosynthesis. Nature 462: 518-521

Petroutsos D, Busch A, Janssen I, Trompelt K, Bergner SV, Weinl S, Holtkamp M, Karst U, Kudla J, Hippler M (2011) The chloroplast calcium sensor CAS is required for photoacclimation in Chlamydomonas reinhardtii. The Plant cell 23: 2950-2963

Terashima M, Petroutsos D, Hudig M, Tolstygina I, Trompelt K, Gabelein P, Fufezan C, Kudla J, Weinl S, Finazzi G, Hippler M (2012) Calcium-dependent regulation of cyclic photosynthetic electron transfer by a CAS , ANR1, and PGRL1 complex. Proceedings of the National Academy of Sciences of the United States of America 109: 17717-17722

Wang L, Yamano T, Takane S, Niikawa Y, Toyokawa C, Ozawa SI, Tokutsu R, Takahashi Y, Minagawa J, Kanesaki Y, Yoshikawa H, Fukuzawa H (2016) Chloroplast-mediated regulation of CO2 -concentrating mechanism by Ca2+-binding protein CAS in the green alga Chlamydomonas reinhardtii. Proceedings of the National Academy of Sciences of the United States of America 113: 12586-12591

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