Roles of the PsbL protein in electron transfer on the donor side of PSII

Abstract

We reported that PsbL protein is involved in the donor side electron transfer of PSII through its carboxyl terminal region. To reveal the role of PsbL in the donor side electron transfer, we carried out two types of experiments. 1. We examined the effect of pH on the PsbL supported electron transfer from TyrZ(D) to P680+. EPR measurements were carried out with spinach PSII core complex (original RC), PsbL-depleted PSII complex (depleted RC) and PsbL-reconstituted PSII complex (reconstituted RC). The signal IIf/s in the original RC and the reconstituted RC showed two step pH dependence with the pK values of 4.5 and 6.5, respectively. In depleted RC, however, the component with pK4.5 was completely disappeared. 2. We tried to introduce the delete mutation of psbL in tobacco plants by homologous recombination into their plastid genome using particle gun to examine the role of PsbL in the PSII function in vivo and obtained homoplasmic-transformed plants lacking PsbL. The resulting transformant had pale green leaves and grew significantly slower than the wild-type control on sucrose-containing medium. This phenotype is similar to that observed in the psbL deletion mutant of cyanobacterium Synechocystis 6803. These facts may suggest that deletion of PsbL depress the function of PSII complex in tobacco. The role of PsbL in the function PSII will be discussed, focusing on the pH dependence of the donor side electron transfer of P680.