MAP KINASES FROM RICE: THE ISOLATION OF cDNA AND FUNCTIONAL ANALYSES BY RETROTRANSPOSON-INDUCED GENE DISRUPTION

National Institute of Agrobiological Resources, Ibaraki 305-8602, Japan

Mitogen-activated protein kinases (MAPKs) are serine/threonine protein kinases that have been found in almost all eukaryotes. In yeast and animals MAPKs are activated by various extracellular signals as well as growth factors and MAPK cascades have been shown to function in signal transduction pathways caused by such environmental stimuli. In plants, however, the function of MAPK is not yet clear although a number of MAPK cDNAs have been identified in several plant species. In this study we characterised rice MAPK homologues and employed genetic approach to dissect the functions of MAPKs. We have isolated eight species of full-length MAPK cDNA clones (OSMPK1 to OSMPK8) from rice cDNA library using partial cDNA fragments as probes, which were isolated by RT-PCR using degenerated oligonucleotides designed from conserved regions of MAPK. The deduced amino acid sequences of these clones revealed 43 kDa to 62 kDa of molecular mass and showed 72% to 86% of identity with other plant MAPKs. Among these cDNAs two MAPK clones had novel type of TXY motif (TDY), whereas other six clones had typical one (TEY). In order to elucidate the regulation mechanism by MAPK in signal transduction pathways, we have tried to isolate mutants in which MAPK gene is disrupted by the insertion of rice retrotransposon Tos17. A population of rice plant in which Tos17 copies were transposed was screened by PCR using a pair of primers: one is specific to Tos17 and another is to MAPK. So far now we have isolated two mutants in which Tos17 is inserted into distinct MAPK genes.