Proteomic analysis of resistance mediated by Rcm 2.0 and Rcm 5.1, two loci controlling resistance to bacterial canker of tomato

Two quantitative trait loci from Lycopersicon hirsutum, Rem 2.0 and Rem 5.1, control resistance to Clavibacter michiganensis subsp. michiganensis, the causal agent of bacterial canker of tomato. Lines containing Rem 2.0 and Rem 5.1 and a susceptible control line were compared at 72 and 144 h postinoculation, using 2-dimensional gel electrophoresis to identify proteins regulated in response to C michiganensis subsp. michiganensis infection. A total of 47 proteins were subjected to tandem mass spectrometry. Database queries with resulting spectra identified tomato genes for 26 proteins. The remaining 21 proteins were either identified in other species or possessed no homology to known proteins. Spectra were interpreted to deduce peptide amino acid sequences that were then used to query publicly available data. This approach identified tomato genes or expressed sequence tags for 44 of the proteins analyzed. Three superoxide dismutase (SOD) enzymes were differentially regulated among genotypes, and patterns of hydrogen peroxide accumulation were genotype- and tissue-specific, indicating a role for oxidative stress in response to C. michiganensis subsp. michiganensis. Steady-state mRNA and protein levels for SOD, thioredoxin M-type, S-adenosylhomocysteine hydrolase, and- pathogenesis-related proteins demonstrated similar patterns of differential regulation. Lines containing Rem 2.0 and Rem 5.1 accumulate different proteins and steady-state mRNAs in response to inoculation, suggesting that the two loci may confer resistance through distinct mechanisms.