Expression of Oryza sativa MAP kinase gene is developmentally regulated and stress-responsive

Mitogen-activated protein kinase (MAPK) pathways are modules involved in the transduction of extracellular signals to intracellular targets in all eukaryotes. In plants, there is evidence for MAPKs playing a role in the signalling of abiotic stresses, pathogens, plant hormones, and cell cycle cues. The large number and divergence of plant MAPKs indicates that this ancient mechanism of signal transduction is extensively used in plants. However, there have been no reports of classical MAPK module in rice. In this report, we have isolated a MAPK from rice (Oryza sativa) termed OsMAPK2. The cloned cDNA is 1457 nucleotides long and the deduced amino acid sequence comprised 369 amino acid residues. Sequence analysis revealed that the predicted amino acid sequence is 72% identical to tobacco wound-induced protein kinase (WIPK). Southern analysis suggested a single OsMAPK2 gene in rice. Analysis at the mRNA level has shown that OsMAPK2 is expressed in all plant organs and high relative amounts of OsMAPK2 were detected in the mature panicles in comparison with in the immature panicles. In suspension-cultured cells, the OsMAPK2 mRNA transcript increased markedly upon temperature downshift from 26 degrees C to 4 degrees C and sucrose starvation. In contrast, the OsMAPK2 mRNA level rapidly declined in rice cell challenged by high temperature. A similarly rapid response of OsMAPK2 was observed in stress-treated seedlings, demonstrating that response of the MAPK pathway occurs also in intact plants. These results suggest that this OsMAPK2 may function in the stress-signalling pathway as well as panicle development in rice.