Mitogen-activated protein kinase (MAPK) cascades have essential roles in diverse intracellular signaling processes in plants, animals and yeasts. In plants, MAPK and MAPK-like kinase activities are transiently activated in response to environmental stresses and plant hormones. In addition, transcription of genes encoding protein kinases involved in MAPK cascades in upregulated by environmental stresses. A possible MAPK cascade of Arabidopsis was identified based on both the yeast two-hybrid analysis and functional complementation analysis of yeast mutants. This MAPK cascade may have important roles in stress signal transduction pathways in Arabidopsis.