Elevated Growth Temperature Can Enhance Photosystem I Trimer Formation and Affects Xanthophyll Biosynthesis in Cyanobacterium Synechocystis sp. PCC6803 Cells.

Klodawska, Kinga and Kovács, László and Várkonyi, Zsuzsanna and Kis, Mihály and Sözer, Özge and Laczkó-Dobos, Hajnalka and Racskóné Domonkos, Ildikó and Gombos, Zoltán (2015) Elevated Growth Temperature Can Enhance Photosystem I Trimer Formation and Affects Xanthophyll Biosynthesis in Cyanobacterium Synechocystis sp. PCC6803 Cells. PLANT AND CELL PHYSIOLOGY, 56 (3). pp. 558-571. ISSN 0032-0781

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Abstract

In the thylakoid membranes of the mesophilic cyanobacterium Synechocystis PCC6803, PSI reaction centers (RCs) are organized as monomers and trimers. PsaL, a 16 kDa hydrophobic protein, a subunit of the PSI RC, was previously identified as crucial for the formation of PSI trimers. In this work, the physiological effects accompanied by PSI oligomerization were studied using a PsaL-deficient mutant (DeltapsaL), not able to form PSI trimers, grown at various temperatures. We demonstrate that in wild-type Synechocystis, the monomer to trimer ratio depends on the growth temperature. The inactivation of the psaL gene in Synechocystis grown phototropically at 30 degrees C induces profound morphological changes, including the accumulation of glycogen granules localized in the cytoplasm, resulting in the separation of particular thylakoid layers. The carotenoid composition in DeltapsaL shows that PSI monomerization leads to an increased accumulation of myxoxantophyll, zeaxanthin and echinenone irrespective of the temperature conditions. These xanthophylls are formed at the expense of beta-carotene. The measured H2O-->CO2 oxygen evolution rates in the DeltapsaL mutant are higher than those observed in the wild type, irrespective of the growth temperature. Moreover, circular dichroism spectroscopy in the visible range reveals that a peak attributable to long-wavelength-absorbing carotenoids is apparently enhanced in the trimer-accumulating wild-type cells. These results suggest that specific carotenoids are accompanied by the accumulation of PSI oligomers and play a role in the formation of PSI oligomer structure.

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