Quality control of Photosystem II: relationship between the thylakoid unstacking and degradation of the D1 protein under light and heat stresses in spinach thylakoids.

Abstract

A common feature of light and heat stresses to chloroplasts is the stress-induced damage to Photosystem II (PSII) complexes. The reaction centre D1 protein is the primary target of the damage. After the damage, a repair mechanism operates to replace the damaged D1 subunits within PSII by a newly synthesized copy. We investigated the relationship between the light- and heat- induced damage to the D1 protein and unstacking of the thylakoids. For efficient migration of the photodamaged PS II complexes from the grana to stroma thylakoids, and also of FtsH proteases from the stroma thylakoids to the grana, the grana stacking becomes a physical hindrance.At lower temperature (4*), the thylakoid unstacking did not take place by strong illumination, and the cleavage of the D1 protein was not observed. These results suggest that the thylakoid unstacking is necessary for efficient degradation of the photo- or heat-damaged D1 protein in PS II.