Symposium II: Reactive oxygen species: balancing signaling and stress
Abs #
20002: Reactive Oxygen Species are mediated by the OXI1-MAPK Pathway: A Hairy Tale of Pathogens, Stress and Development
Mitogen-activated protein kinase (MAPK) pathways transduce a large variety of external signals in all eukaryotes including plants. MAPK pathways are minimally composed of a three-kinase-module composed of a MAPK, a MAPK kinase, and a MAPK kinase kinase (1). We are studying MAPKs involved in stress signaling. We have found that the Medicago SIMK MAPK is highly expressed in the root epidermis and trichoblasts. During root hair formation, SIMK is found to be associated with vesicles and actin filaments at the root hair tip. MAPK inhibitor treament blocks growth of root hairs, and overexpression of active SIMK enhances root hair growth, indicating that SIMK is necessary for polarized growth (2). In agreement with the requirement of ethylene signaling for root hair development, SIMK was found to be part of the ethylene pathway, and hyperactive SIMK kinase plants show a constitutive triple response phenotype with extended root hairs (3).
Root hair growth is also dependent on the production of reactive oxygen species (ROS) and mutants with a defective NADPH oxidase are defective in root hair formation. ROS activate the MAPKs MPK3/6 in Arabidopsis, suggesting that ROS and ethylene signals converge in root hairs at the level of the MAPK pathway. Recently, we have isolated OXI1 as an upstream kinase of ROS-induced MPK3/6 and oxi1 mutants show a defective root hair phenotype (4). ROS are also involved in abiotic stress responses and pathogen defence. Accordingly, oxi1 mutants are compromised in basal defence against a fungal pathogen.
1.Jonak, C. Ökresz, L., Bögre, L., and Hirt, H. (2002) Complexity, cross talk and integration of plant MAP kinase signalling. Curr. Op. Plant Biol. 5, 415-424.
2.Samaj, J., Ovecka, M., Hlavacka, A., Ouaked, F., Meskiene, I., Salaj, J., Lichtscheidl, I., Volkmann, D., Bögre, L., Baluska, F., and Hirt, H. (2002) Involvement of the mitogen-activated protein kinase SIMK in regulation of root hair tip-growth. EMBO J. 21, 3296-3306.
3.Ouaked, F., Rozhon, W., Lecourieux, D., and Hirt, H. (2003) A MAPK pathway mediates ethylene signaling in plants. EMBO J. 22, 1282-1288.
4.Rentel, M.C., Lecourieux, D., Ouaked, F., Usher, S.L., Petersen, L., Okamoto, H., Knight, H., Peck, S.C., Grierson, C.S., Hirt, H. and Knight, M.R. (2004) OXI1 kinase is necessary for oxidative burst-mediated signalling in Arabidopsis. Nature 427, 858-861.
