Proteomic insights into oligogalacturonide signalling in plant defence and development

Oligogalacturonides (OGs) are fragments derived from the hydrolysis of plant cell wall homogalacturonan by fungal endo-polygalacturonases and are well known damage-associated molecular patterns (DAMPs). In Arabidopsis thaliana, perception of OGs triggers an intracellular signaling cascade that initiates defense against pathogens. OGs may also work as regulators of plant growth and development mainly through their antagonism with auxin (IAA). However, most of the mechanism by which the OG signal is transduced is not yet known. In this study, quantitative phosphoproteomics was applied to investigate the initial signaling events specifically activated by OG signaling. Analysis of quantitative changes in the proteome and phosphoproteome, determined by dimethyl labelling and LC/MSMS analysis in a membrane-enriched fraction, revealed rapid phosphorylation changes, with no substantial changes in overall protein abundance after a 10 min treatment with OGs. We also analyzed the changes in the nuclear proteome in response to IAA, OGs or a IAA/OG co-treatment, to identify regulatory elements that mediate the inhibition of the auxin-induced responses by OGs. The analysis of proteomic and transcriptomic data suggests that changes in abundance of nuclear proteins in response to OGs/IAA may arise not only from enhanced or reduced expression but also from post-translational modifications, degradation and/or translocation of proteins to different compartments. Some interesting candidates in OG/IAA antagonism have been identified and their functional role is under study.