392 Plant mitogen-activated protein kinase signaling cascades Guillaume Tena*, Tsuneaki Asai†, Wan-Ling Chiu‡ and Jen Sheen§ Mitogen-activated protein kinase (MAPK) cascades have components that link sensors/receptors to target genes emerged as a universal signal transduction mechanism that and other cellular responses. connects diverse receptors/sensors to cellular and nuclear responses in eukaryotes. Recent studies in plants indicate that In the past few years, it has become apparent that mitogen- MAPK cascades are vital to fundamental physiological functions activated protein kinase (MAPK) cascades play some of the involved in hormonal responses, cell cycle regulation, abiotic most essential roles in plant signal transduction pathways stress signaling, and defense mechanisms. New findings have from cell division to cell death (Figure 1). MAPK cascades revealed the complexity and redundancy of the signaling are evolutionarily conserved signaling modules with essen- components, the antagonistic nature of distinct pathways, and tial regulatory functions in eukaryotes, including yeasts, the use of both positive and negative regulatory mechanisms. worms, flies, frogs, mammals and plants. The recent enthu- siasm for plant MAPK cascades is backed by numerous Addresses studies showing that plant MAPKs are activated by hor- Department of Molecular Biology, Massachusetts General Hospital, mones, abiotic stresses, pathogens and pathogen-derived Department of Genetics, Harvard Medical School, Wellman 11, elicitors, and are also activated at specific stages during the 50 Blossom Street, Boston, Massachusetts 02114, USA cell cycle [2]. Until recently, studies of MAPK cascades in *e-mail:
[email protected] †e-mail:
[email protected] plants were focused on cDNA cloning [3,4] and used a ‡e-mail:
[email protected] MAPK in-gel assay, MAPK and tyrosine-phosphate anti- §e-mail:
[email protected] bodies, and kinase inhibitors to connect signals to MAPKs Current Opinion in Plant Biology 2001, 4:392–400 [2].