The plant homologue of MAP kinase is expressed in a cell cycle-dependent and organ-specific manner.

In animals, MAP kinase plays a key role in growth factor-stimulated signalling and in mitosis. The isolation of a Medicago sativa cDNA clone MsK7 which shows 52% identity to animal MAP kinases is reported. The deduced protein sequence shows all the important structural features of MAP kinases and also contains the highly conserved Thr-183 and Tyr-185 residues. Northern analysis of synchronized alfalfa cells showed that the MsK7 kinase gene is expressed at low levels in G1 phase but at higher levels in S and G2 phases of the cell cycle. In the plant, only stems and roots were found to contain MAP kinase MsK7 mRNA. Southern and PCR analyses indicated that alfalfa contains at least four highly related MAP kinase genes.