Deg1 is involved in the degradation of the PsbO oxygen-evolving protein of photosystem II in Arabidopsis

Deg1, a thylakoid lumen-localized protease, retains both chaperone and protease activities. The in vivo function of Deg1 has been shown to be involved not only in PSII assembly but also in the degradation of PSII reaction center protein D1. Here we used the transgenic plants with reduced Deg1 to examine whether the lumen-localized proteins are also the substrates of Deg1 in vivo. Our results showed that the transgenic plants accumulated degradation products of the PsbO protein while the levels of full-length PsbO were not affected. The PsbO degradation products could be efficiently degraded by the recombinant Deg1. These results suggest that Deg1 is involved in the degradation of the PsbO degradation fragments, but not in the initial cleavage event itself.