Label-Free Quantitative Proteomics Analysis in Susceptible and Resistant Brassica napus Cultivars Infected with Xanthomonas campestris pv. campestris

Black rot, caused by Xanthomonas campestris pv. campestris (Xcc), is the main disease of cruciferous vegetables. To characterize the resistance mechanism in the Brassica napus–Xcc pathosystem, Xcc-responsive proteins in susceptible (cv. Mosa) and resistant (cv. Capitol) cultivars were investigated using gel-free quantitative proteomics and analysis of gene expression. This allowed us to identify 158 and 163 differentially expressed proteins following Xcc infection in cv. Mosa and cv. Capitol, respectively, and to classify them into five major categories including antioxidative systems, proteolysis, photosynthesis, redox, and innate immunity. All proteins involved in protein degradation such as the protease complex, proteasome subunits, and ATP-dependent Clp protease proteolytic subunits, were upregulated only in cv. Mosa, in which higher hydrogen peroxide accumulation concurred with upregulated superoxide dismutase. In cv. Capitol, photosystem II (PS II)-related proteins were downregulated (excepting PS II 22 kDa), whereas the PS I proteins, ATP synthase, and ferredoxin-NADP⁺ reductase, were upregulated. For redox-related proteins, upregulation of thioredoxin, 2-cys peroxiredoxin, and glutathione S-transferase occurred in cv. Capitol, consistent with higher NADH-, ascorbate-, and glutathione-based reducing potential, whereas the proteins involved in the C₂ oxidative cycle and glycolysis were highly activated in cv. Mosa. Most innate immunity-related proteins, including zinc finger domain (ZFD)-containing protein, glycine-rich RNA-binding protein (GRP) and mitochondrial outer membrane porin, were highly enhanced in cv. Capitol, concomitant with enhanced expression of ZFD and GRP genes. Distinguishable differences in the protein profile between the two cultivars deserves higher importance for breeding programs and understanding of disease resistance in the B. napus–Xcc pathosystem.