Degradation of the D1 protein of Photosystem II in Synechocystis PCC6803 under light and heat stresses-The role of an FtsH protease

Abstract

Cell growth, oxygen-evolving activity and degradation of the D1 protein of PS II were examined with WT and ΔFtsH (slr0228) mutant of Synechocystis PCC6803 under light or heat stress. WT grew normally under light stress (70μEm^-2s^-1) or heat stress (40^oC) conditions, while ΔFtsH cells showed bleaching of pigments under these conditions. Oxygen evolution of WT cells was not affected by light stress (500μEm^-2s^-1) or heat stress (42^oC) unless lincomycin was added, while that of the mutant suffered from the stresses irrespective of the presence or absence of lincomycin. Western blot analysis showed a decrease in the D1 protein upon light or heat treatment of the WT cells. By contrast, loss of the D1 protein was not observed with the mutant cells. These results suggest that the FtsH protease is involved in the degradation of the D1 protein both under light and heat stress.