Proteomics approaches to understand protein phosphorylation in pathway modulation

Signaling pathways in all organisms consist of series of phosphorylation and dephosphorylation events that define directionality and allow different levels of feedback-regulation. Mass spectrometry-based proteomic analyses in recent years have led to a proteome-wide identification of thousands of phosphorylation sites in various plant species. Given this magnitude of mostly qualitative information about protein phosphorylation, discovery of specific phosphoproteins with regulatory functions represents a major challenge. In future large-scale experiments, combinations of data-driven modeling strategies based on quantitative data, targeted kinase–substrate screens, and verification in biochemical and genetic experiments are required to specifically spot phosphorylation sites with specific roles in signaling pathway modulation.