Plant Molecular Biology Reporter 23: 331-343, December 2005 9 2005 bzternational Society for Plant Molecular Biology. Printed in Canada. Review Genomic Analysis of MAP Kinase Cascades in Arabidopsis Defense Responses MARINA CVETKOVSKA I, CHRISTOF RAMPITSCH ~, NATALIA BYKOVA 2 and TIM XING 1'* 1Department of Biology and hzstitute of Biochemistry., Carleton Universi~, Ottawa, ON K1S 5B6, Canada; "-Agriculture and Agri-Food Canada, Cereal Research Centre, Winnipeg MB Canada R3T 2M9 Abstract. The process of phosphorylation and dephosphorylation is a common mechanism of signal transduction in plants, connecting the perception of extracellular signals with the final responses to those signals. This paper will concentrate on the mitogen-activated protein (MAP) kinase pathway, one of the main phosphorylation pathways that plants use in biotic and abiotic stress resistance. It is a cascade consisting of several classes of kinases, each having a different role in signal integration and divergence. The cascade is regulated by various mechanisms, including not only transcriptional and translational regulations but also post-transcriptional regulations and protein-protein interactions. Recent detailed analysis of certain specific MAP kinase pathways has revealed the speci- ficity of the kinases in the cascade, signal transduction patterns, identity of pathway targets, and the complexity of the cascade. Strategies in the study of phosphorylation pathways are discussed, and approaches integrating various genomics and proteomics technologies are suggested. 1. Introduction Plant diseases have been known from the very beginnings of organized agriculture and have frequently been associated with hunger and suffering. One of the most famous examples in history is the Irish potato famine of the 1840s, caused by late blight of potato, whose agent, the fungus Phytophthora infestans, is the so-called "plant destroyer" (Holub, 2001). Since then, new ways to protect crops from disease and to increase their productivity have evolved, for example, through the use of pesticides and higher yielding plant varieties. Today, with the emergence of new genetic and biomolecular techniques, it becomes possible to understand more fully, and potentially to enhance, the plant's defense mechanism and thus produce crops that are more resistant to disease. Arabidopsis thaliana was first used as a model plant for the study of plant- pathogen interactions about 20 years ago. Since then there has been exceptional progress in discovering the molecular and genetic basis for disease resistance in this plant (Buell, 1998). Arabidopsis was chosen as a model for several reasons. It *Author for correspondence, e-mail: Tim_Xing@Carleton.ca; tel: (613) 520-2600 ext 8981; fax: (613) 520-3539.