Early Signaling in plant immunity

PAMP triggered immunity (PTI) and Effector triggered Immunity (ETI) are two forms of disease resistance mounted by plants to fight pathogen infection. Either ETI or PTI can trigger systemic acquired resistance (SAR), which requires elevated Salicylic Acid (SA) levels and consequent redox activation of NPR1. In order to determine the proteins that change in abundance, phosphorylation or redox state during early defense signaling, we used liquid chromatography electro-spray ionization tandem mass spectrometry (LC ESI MSMS) to survey the Arabidopsis thaliana leaf proteome following 5 minutes BTH treatment. BTH is a potent analog of SA. Changes in protein abundance were determined by extracting total protein, converting proteins to tryptic peptides, labeling the peptides with iTRAQ mass tags, and comparing the iTRAQ tag intensities from the different samples to each other. The levels of 7153 proteins were compared and 49 proteins were observed to change in abundance following BTH treatment. A total of 2,384 phosphopeptides were observed and of these 45 proteins changed in phosphorylation. Changes in redox state were determined by using LC ESI MSMS to observe proteins that differentially bound to a mutant thioredoxin column, which selectively binds proteins containing disulfide bonds. Of the 2,260 identified proteins, 249 proteins were observed to change in redox state following BTH treatment. Pseudomonas syringae infection of the knockout mutants of 6 of our identified proteins resulted in enhanced disease susceptibility phenotypes that have not been previously reported, therefore giving us new insight into the role of these different proteins in plant defense.