Plant Homologues of Components of MAPK (Mitogen-Activated Protein Kinase) Signal Pathways in Yeast and Animal Cells

As they respond to numerous extracellular and intracellularstimuli, plants develop various morphological features and thecapacity for a large variety of physiological processes duringtheir growth. If we are to understand the molecular basis ofsuch developments, we must elucidate the way in which signalsgenerated by such stimuli can be transduced into plant cellsand transmitted by cellular components to induce the appropriateterminal events. In yeast and animal systems, signal pathwaysthat are known collectively as MAPK (mitogen-activated proteinkinase) cascades have been shown to play a central role in thetransmission of various signals. The components of these pathwaysinclude the MAPK family, the activator kinases of the MAPK family(the MAPKK family) and the activator kinases of the MAPKK family(the MAPKKK family). The members of each respective family arestructurally conserved and signals are transmitted by similarphosphotransfer reactions at corresponding steps that are mediatedby a specific member of each family in turn. Both cDNAs andgenes that encode putative homologues of these components haverecently been isolated from plant sources. Some of them havebeen shown to be related not only structurally but also functionallyto members of the MAPK cascades of other organisms. These findingssuggest that plants have signal pathways that are analogousto the MAPK cascades in yeast and animal cells but it remainsto be proven that plant homologues do in fact constitute kinasecascades. Given the presence of so many homologues of MAPKsand MAPKKKs in a single plant species, namely, Arabidopsis thaliana,we can be fairly confident that the putative MAPK cascades areinvolved in various physiological processes in plants. (Received March 28, 1995; )