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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

The High Light-Inducible Polypeptides Stabilize Trimeric Photosystem I Complex under High Light Conditions in Synechocystis PCC 6803^{1,[C],[W],[OA]}

Department of Applied Science, University of Arkansas, Little Rock, Arkansas 72204

The high light-inducible polypeptides (HLIPs) are critical for survival under high light (HL) conditions in Synechocystis PCC 6803. In this article, we determined the localization of all four HLIPs in thylakoid protein complexes and examined effects of hli gene deletion on the photosynthetic protein complexes. The HliA and HliB proteins were found to be associated with trimeric photosystem I (PSI) complexes and the Slr1128 protein, whereas HliC was associated with PsaL and TMP14. The HliD was associated with partially dissociated PSI complexes. The PSI activities of the hli mutants were 3- to 4-fold lower than that of the wild type. The hli single mutants lost more than 30% of the PSI trimers after they were incubated in intermediate HL for 12 h. The reduction of PSI trimers were further augmented in these cells by the increase of light intensity. The quadruple hli deletion mutant contained less than one-half of PSI trimers following 12-h incubation in intermediate HL. It lost essentially all of the PSI trimers upon exposure to HL for 12 h. Furthermore, a mutant lacking both PSI trimers and Slr1128 showed growth defects similar to that of the quadruple hli deletion mutant under different light conditions. These results suggest that the HLIPs stabilize PSI trimers, interact with Slr1128, and protect cells under HL conditions.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Qingfang He (qfhe{at}ualr.edu).

^[C] Some figures in this article are displayed in color online but in black and white in the print edition.

^[W] The online version of this article contains Web-only data.

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www.plantphysiol.org/cgi/doi/10.1104/pp.108.121087

^* Corresponding author; e-mail qfhe{at}ualr.edu.

Received April 11, 2008; accepted May 19, 2008; published May 23, 2008.