Switching the flip: protein phosphatase roles in signaling pathways.

Protein phosphatases are the obligate partners of protein kinases in cellular control circuitry. Several specific roles of phosphatases have been revealed in plant systems through recent work capitalizing on functional genomics, interaction screens and activation-tagging approaches. Historically, the redundancy of genes that encode phosphatase functions has impeded genetic analysis in plant systems, and relatively few elucidated signaling pathways include protein phosphatases that have clearly defined substrates. Functional genomics, interaction and suppression screens, activation tagging and phosphoproteomics now hold great promise for identifying phosphatases that are active in signaling and regulation, and for revealing their in vivo substrates. This level of analysis will be essential for a full understanding of the effects of reversible protein phosphorylation in modulating and integrating cellular activities.