Mitogen‐Activated Protein Kinase Cascades in Plant Signaling

Abstract Plants have an expanded family of mitogen‐activated protein kinases (MAPKs) in comparison with yeast and animals. Analysis of the completely sequenced Arabidopsis , poplar, and rice genomes revealed 20, 21, and 15 members, respectively. These MAPKs have the potential to form numerous functional cascades with their upstream MAPK kinases (MAPKKs or MEKs) and MAPKK kinases (MAPKKKs or MEKKs). Biochemical and genetic analyses demonstrated that plant MAPK cascades play important roles in signaling plant growth, development, and response to environmental cues. It is also becoming clear that different functional cascades frequently share common components, suggesting complicated signaling networks centered on these MAPKs. How specificity is maintained when distinct functional pathways share common components is central to our understanding of plant intracellular signaling. Future research aimed at identifying upstream receptors/sensors and downstream MAPK substrates will reveal the molecular mechanisms underlying MAPK functions and shed light on how signaling specificity is maintained.