A Heat-Stress Pulse Inactivates a 50 kDa Myelin Basic Protein Kinase in Tomato

A heat-activated MAP kinase in tomato: a possible regulator of the heat stress response

Adaptation to elevated temperatures is of major importance for the survival of plants. The role of kinases in heat stress response was studied in tomato by in gel and in solution kinase assays using myelin basic protein as substrate. The application of heat stress in a naturally occurring temperature range resulted in a fast and transient activation of a 50 kDa mitogen-activated protein (MAP) kinase both in a photoautotrophic cell suspension culture and in leaves of mature plants. The heat activation of the MAP kinase was shown to be calcium-dependent. The specific phosphorylation of tomato heat stress transcription factor HsfA3 by a partially purified preparation of the heat-activated MAP kinase supports a physiological role of the identified kinase activity in transducing the heat stress signal.

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.

Mitogen-activated protein [MAP] kinase pathways in plants: versatile signaling tools

Mitogen-activated protein kinases (MAPKs) are important signaling tools in all eukaryotes, and function in mediating an enormous variety of external signals to appropriate cellular responses. MAPK pathways have been studied extensively in yeast and mammalian cells, and a large body of knowledge on their functioning has accumulated, which is summarized briefly. Plant MAPK pathways have attracted increasing interest, resulting in the isolation of a large number of different components of MAPK cascades. Studies on the functions of these components have revealed that MAPKs play important roles in the response to a broad variety of stresses, as well as in the signaling of most plant hormones and in developmental processes. Finally, the involvement of various plant phosphatases in the inactivation of MAPKs is discussed.