Abstract
PsbP, an extrinsic subunit of photosystem II (PSII), has been reported to be present only in plants and green algae. However, recent genomic and proteomic studies have demonstrated the presence of PsbP homolog in cyanobacteria (CyanoP), whereas CyanoP was reported to be rarely associated with PSII. This suggests that the function of CyanoP and PsbP are quite different, and PsbP should have developed as an important factor of PSII regulation during evolution of photosynthetic oxygenic organisms. Consistent with this suggestion, it has been reported that higher plants still have PsbP-like (PPL) proteins, which show higher homology with CyanoP than PsbP. In Arabidopsis thaliana, there are two PPL proteins and we named these proteins as PPL1 and PPL2. Characterization of ppl1 and ppl2, mutants lacking PPL1 and PPL2 proteins, respectively, is on-going to elucidate their functions.
