Identification of wheat proteins with altered expression levels in leaves infected by the stripe rust pathogen

Plants exhibit resistance to incompatible pathogens by localized and systemic defense responses. In this study, a proteomics approach was used to study compatible and incompatible interactions between wheat and Puccinia striiformis f. sp. tritici (Pst). Seedlings of wheat cv. Suwon 11 were inoculated with isolates of compatible race CYR31 and incompatible race CYR23. Total proteins isolated from wheat leaves were separated by two-dimensional gel electrophoresis. Compared with the mock inoculation, 41 differentially expressed proteins at 24 and 72 h post-inoculation were analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), and 23 of these proteins were positively identified. Of those, six were further examined for changes at the transcriptional level in wheat leaves infected with Pst. They were categorized into classes related to photosynthesis, antioxidant defense, signal transduction, and metabolism. Annotation of proteins induced in incompatible interactions revealed a rapid resistance response that included the induction of protein kinase signaling and the production of reactive oxygen species, which usually occur during R-gene-mediated responses. Proteins with antioxidant functions, e.g., ascorbate peroxidase, dehydroascorbate reductase, and glutathione S-transferase, were differentially expressed between compatible and incompatible interactions, indicating differential accumulation of reactive oxygen species in infected tissues. In addition, fragments of ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) were identified in proteins isolated from Pst-infected leaves. Rubisco fragmentation in response to Pst inoculation was confirmed by western blot analysis, indicating that chloroplasts and photosynthesis in both the incompatible and compatible situations were affected by Pst infection.