Proteomic analysis of the oxygen-evolving complex of photosystem II under biotec stress: Studies on Nicotiana benthamiana infected with tobamoviruses

We have previously shown that tobamovirus infection induces an inhibition of photosystem II electron transport, disturbing the oxygen‐evolving complex (OEC). In the infected plants, the OEC polypeptide pattern was modified when compared to healthy plants, the levels of the PsbP and PsbQ extrinsic proteins being lowered to different extents. In this work we have further investigated by two‐dimensional polyacrylamide gel electrophoresis (2‐DE) the changes on the OEC protein pattern of thylakoid membranes isolated from Nicotiana benthamiana Domin plants infected with the Spanish strain of pepper mild mottle virus. When the thylakoid membranes from healthy plants were analyzed for the presence of PsbO and PsbP proteins by 2‐DE (pI range 4–7) and further immunoassayed by using specific‐antisera against these two proteins, it was observed that four polypeptides cross‐reacted with each antiserum. These data, along with the N‐terminal amino acid sequence determined for the eight polypeptides, indicate that the N. benthamiana PsbO and PsbP proteins correspond to protein families. In the silver‐stained 2‐DE gels of thylakoid membranes isolated at different days postinoculation from virus‐infected plants, it was observed that the content of PsbP polypeptides decreased dramatically with respect to those of PsbO, during the progress of the infection. Interestingly, there was a differential decrease of the different PsbP proteins, indicative of a distinct regulation of their expression.