Phosphoproteomics of early oligogalacturonides signaling in Arabidopsis

During the infection of a plant tissue by phytopathogenic fungi, homogalacturonan, the main component of pectin, is broken down into fragments called oligogalacturonides (OGs) by the action of fungal polygalacturonases. The interaction between polygalacturonases and their inhibitors (polygalacturonase-inhibiting proteins: PGIPs) in the plant cell wall favours the formation of OGs with degree of polymerization from 10 to 15 that function as signals for the activation of the plant innate immune response. Although the effects of OGs in plant defence are well recognised, the perception/transduction mechanisms of these elicitors are still not completely described. By a 2D-DIGE approach coupled with the quantitative phospho-specific stain ProQ Diamond we studied the early events of phosphorylation in Arabidopsis thaliana in response to OGs. Soluble proteins and prefractionated total membranes were analyzed and the differential phosphorylated proteins were identified by MALDI-ToF mass spectrometry. Phosphorylation changes were detected in several oxidative stress-related proteins that included heat shock proteins, jasmonate-inducible jacalin proteins and H+-ATPases, among which the vacuolar-H+ATPase encoded by DET3 gene. Phosphorilation changes were also detected in plasma membrane proteins like AtPcaP1, a plasma membrane-bounded protein involved in the cross-talk between Ca+2 signaling and PtdInsPs in the intracellular signaling pathway.