PROGRESS IN STUDIES OF PLANT HOMOLOGS OF MITOGEN-ACTIVATED PROTEIN (MAP) KINASE AND POTENTIAL UPSTREAM COMPONENTS IN KINASE CASCADES

Mitogen-activated protein (MAP) kinase cascades were originally identi fied as protein phosphorylation systems that control the division and the growth of yeast and animal cells. Such cascades consist of MAP kin ases, MAP-kinase kinases, and MAP-kinase-kinase kinases. In addition, these organisms have been also shown Co have structurally related but functionally different MAP kinase cascades, which are involved in vari ous cellular processes such as a response to osmotic stress and apopto sis. Plants also have been shown to have a number of members of each k inase family. Although physiological and genetic functions of most pla nt members have yet to be established, some of members have been shown to be responsible for the cellular transmission of signals generated by wounding or a mechanical stress, which predicts that MAP kinase cas cades may function in a variety of physiological processes in the plan t cells. In the present review, we summarize recent progresses of rese arches on plant members of each kinase family as well as those of anal yses of the cascades in other organisms.