THE SAM KINASE PATHWAY - AN INTEGRATED-CIRCUIT FOR STRESS SIGNALING IN PLANTS

Mitogen-activated protein (MAP) kinases are universal transducers of e xtracellular signals in all eukaryotes. Multiple MAPK pathways exist i n each organism that are differentially activated by a variety of stim uli including chemical as well as physical factors. We have characteri zed the stress-activated MAP kinase (SAMK) pathway in plants that is i nvolved in mediating touch, drought, cold, and wounding. The SAMK path way is activated by a posttranslational mechanism, but inactivation re quires de novo expression of gene(s). One of these genes is MP2C encod ing a protein phosphatase type 2C that is able to inactivate the SAMK pathway. MP2C expression itself is regulated by the SAMK pathway and c onstitutes a negative feedback mechanism for resetting the pathway.