Abstract
To avoid photoinhibition, an efficient degradation of D1 protein in the repair cycle of photosystem II is important. Mounting evidence indicates that FtsH, an ATP-dependent metalloprotease in thylakoid membranes, plays a key role in this process. On the other hand, light-induced phosphorylation of D1 is suggested to regulate D1 degradation, provided that phosphorylated D1 may be a poor substrate of proteases. During light irradiation, phosphorylated-D1 level was assayed in mature leaves of Arabidopsis var2 (lacking FtsH2) using immuno-blot against anti-phosphothreonine antibodies. These assays showed that the phosphorylated D1 was readily accumulated in var2 compared with wild-type, suggesting the connection between D1 degradation and phosphorylation. In this study, we further attempt to in vivo assess the role of phosphorylation, mediated by a novel STN8 kinase in D1 degradation. To do this, a double mutant var2 and stn8 was generated. Photosynthetic properties of the double mutant will be presented.
