Abstract
NIMA-related kinases (NEKs) consist a family of Ser/Thr protein kinases in eukaryotes. In fungi and animal cells, NEKs regulate mitotic events including G2/M transition, centrosome separation, and spindle formation. To elucidate plant NEK functions, we analyze seven NEK members encoded in the genome of Arabidopsis thaliana. Subcellular localization analysis demonstrates that all of the seven NEKs associate with microtubules. NEK6 interacts with NEK4 and NEK5, phosphorylates tubulin and armadillo-repeat containing kinesin 1 (ARK1), and regulates epidermal cell expansion through suppression of excessive microtubule stabilization. Multiple mutant analysis demonstrates that NEK1, NEK2, and NEK3 regulate directional cell expansion in root epidermal cells. In addition, NEK4, NEK5, NEK6, and NEK7 are implicated in stress response. To identify signaling component downstream of NEKs, we isolate several proteins interacting with NEK6 by using immunoprecipitation and yeast two-hybrid analysis. These results suggest that plant NEKs interact with each other and regulate cell expansion and stress response. The functional redundancy and diversification of plant NEKs will be discussed.
