Modes of MAPK substrate recognition and control

• The current knowledge about substrates of the key stress regulatory kinase MPK3 is compiled.
• Experimental approaches in mitogen-activated protein kinase (MAPK) research, and their pro and cons are described.
• General patterns of the occurrence and distribution of peptide motifs related to MAPK control are defined.
• Models of how the MAPK recognises, binds and phosphorylates its targets are proposed.

Mitogen-activated protein kinase (MAPK) cascades are universal, evolutionary conserved signalling modules, which translate environmental information into appropriate responses via phosphorylation of their substrate proteins. In Arabidopsis, the MAPK MPK3 regulates numerous cellular processes, including the adaptation to abiotic and biotic stresses. The molecular steps immediately downstream of MPK3 induction have, therefore, received abundant attention, and a respectable number of MPK3 targets are known by now. These proteins illustrate the substrate promiscuity of MPK3. They also are evidence for how manifold phosphorylation-regulated functions can be. This review presents the current knowledge about the function and regulation of MPK3-targeted proteins, takes a close look at their primary protein sequences, and proposes a model of how MPK3 recognises, binds, and phosphorylates its targets.