Proteomic analysis of defense response of wildtype Arabidopsis thaliana and plants with impaired NO- homeostasis.

In recent years, nitric oxide (NO) has been recognized as a signalling molecule of plants, being involved in diverse processes like germination, root growth, stomatal closing, and responses to various stresses. A mechanism of how NO can regulate physiological processes is the modulation of cysteine residues of proteins (S-nitrosylation) by S-nitrosoglutathione (GSNO), a physiological NO donor. The concentration of GSNO and the level of S-nitrosylated proteins are regulated by GSNO reductase, which seems to play a major role in NO signalling. To investigate the importance of NO in plant defense response, we performed a proteomic analysis of Arabidopsis wildtype and GSNO-reductase knock-out plants infected with both the avirulent and virulent pathogen strains of Pseudomonas syringae. Using 2-D DIGE technology in combination with MS, we identified proteins, which are differentially accumulated during the infection process. We observed that both lines were more resistant to avirulent infections than to virulent infections mainly due to the accumulation of stress-, redox-, and defense-related proteins. Interestingly, after virulent infections, we also observed accumulation of defense-related proteins, but no or low accumulation of stress- and redox-related proteins, respectively. In summary, we present here the first detailed proteomic analysis of plant defense response.