Rice mitogen-activated protein kinase gene family and its role in biotic and abiotic stress response

The mitogen-activated protein kinase (MAPK) cascade is an important signaling module that transduces extracellular stimuli into intracellular responses in eukaryotic organisms. An increasing body of evidence has shown that the MAPK-mecliated cellular signaling is crucial to plant growth and development, as well as biotic and ablotic stress responses. To date, a total of 17 MAPK genes have been identified from the rice genome. Expression profiling, biochemical characterization and/or functional analysis were carried out with many members of the rice MAPK gene family, especially those associated with biotic and abiotic stress responses. In this review, the phylogeneitic relationship and classification of rice MAPK genes are discussed to facilitate a simple nomenclature and standard annotation of the rice MAPK gene family. Functional data relating to biotic and ablotic stress responses are reviewed for each MAPK group and show that despite overlapping in functionality, there is a certain level of functional specificity among different rice MAP kinases. The future challenges are to functionally characterize each MAPK, to identify their downstream substrates and upstream kinases, and to genetically manipulate the MAPK signaling pathway in rice crops for the improvement of agronomically important traits.