potyvirus P1 protein interacts with the Rieske Fe/S protein of its host

Yeast two-hybrid (Y2H) screens were used to test for interactions between the P1 protein of Soybean mosaic virus Pinellia isolate (SMV-P) and a cDNA expression library of its host, the aroid Pinellia ternata. Of the 13 independent interacting clones identified, ten were identical and had an open reading frame predicted to encode a 23.7-kDa protein closely related to the cytochrome b6/f complex Rieske Fe/S genes of plants. The interaction between SMV-P-P1 and the mature Rieske Fe/S protein (without transit peptide) of the host was confirmed by in vitro co-immunoprecipitation of the two proteins. Y2H assays using different parts of the two proteins showed that only the N-terminal part (amino acids 1-82) of SMV-P P1 was responsible for the interaction with the Rieske Fe/S protein and that amino acids 1-33 interacted only with the transit peptide, while amino acids 34-82 could interact with the entire Rieske Fe/S protein. SMV-P P1 also interacted moderately with the Rieske Fe/S protein of its other hosts, soybean and Zantedeschia aethiopica, but weakly with that of the non-host Arabidopsis thaliana. The P1-Rieske Fe/S protein interactions are likely to be involved in symptom development, and the very variable N-terminus of P1 may play an important role in host adaptation.