Mitogen-activated protein kinases (MAPKs) pathways are modules involved in the transduction of extracellular signals to intracellular targets in all eukaryotes. Distinct MAPK pathways are regulated by different extracellular stimuli and are implicated in a wide variety of biological processes. In plants, there exists a large number of highly conserved MAPK genes. The presently available evidence indicates that some of these MAPKs play a role in signal transduction of abiotic stress, pathogens, plant hormones, and cell cycle cues.