Interaction of DspE/A, a pathogenicity/avirulence protein of Erwinia amylovora, with pre-ferredoxin from apple and its relationship to photosynthetic efficiency.

摘要

DspE/A is a disease-specific gene of Erwinia amylovora that is required for development of fire blight in host plants such as apple and pear. In spite of its functional significance in terms of host-pathogen interaction, the mode of action of DspE in plant cells is not understood. In this study, we identified and characterized a precursor-ferredoxin from apple (Pre-Fd) that interacts with DspE/A. The sequence of Pre-Fd is highly similar to that of many plant Pre-Fd proteins. On import into chloroplasts, Pre-Fd is converted to ferredoxin (Fd), where it serves as an electron carrier in photosystem I (PS I). Pull-down binding assays confirmed physical interaction between intact DspE/A and Pre-Fd, in vitro. GFP-labeled Pre-Fd was localized to chloroplasts and His-tagged purified Fd showed notable electron transfer activity in vitro. Interestingly, DspE/A interacted only with Pre-Fd and not with Fd. This suggested that interaction occurs in the cytoplasm before Pre-Fd is imported into chloroplasts. Fd dependent photosynthetic activity was inhibited in young apple leaves of trees inoculated with E. amylovora, but not with a dspE/A mutant or with buffer. Overall, these studies suggest that DspE/A inhibits photosynthesis in young leaves, by blocking import of Pre-Fd into developing chloroplasts; the interaction may facilitate pathogenesis by limiting photosynthesis in developing leaves..