Analysis of the Arabidopsis Mitogen-Activated Protein Kinase Families: Organ Specificity and Transcriptional Regulation upon Water Stresses

The Arabidopsis genome contains 20 MPK, 10 MKK, 60 MAP3K, and 10 MAP4K genes, but the functions of the corresponding proteins are still poorly characterized. To research possible functional MAP kinase modules involved in water stress signalling, original macroarrays were developed for their sensitivity and specificity. The expression patterns of the MPK and MKK gene families, as well as selected key members of the MAP3K and MAP4K families, were studied in relation to organ specificity and to various water stresses. Several kinases of the scarcely studied MPK group containing a TDY activation motif were induced by water stresses. There are four different MPKs (MPK9, MPK11, MPK17, and MPK18), among which three contain the TDY activation motif, and MKK9 and MAP3K6 are induced at the transcriptional level by dehydration, salinity, and hyperosmolarity treatments. They probably constitute MAP kinase key elements involved in water stress signalling.