Abstract
NIMA-related kinases (NEKs) are a family of Ser/Thr protein kinases conserved in eukaryotes and implicated in cell cycle regulation. Arabidopsis NEK6 interacts with armadillo-repeat kinesins (ARKs) and modulates directional expansion of epidermal cells (Motose et al., 2008; Sakai et al., 2008). Here, we describe functional analysis of NEK family in Arabidopsis with special emphasis on NEK6. NEK6 was highly accumulated during cell division and cell expansion and concentrated in dot-like structures exhibiting dynamic movement along with cortical microtubules and phragmoplasts. The kinase assay and microtubule imaging indicated that NEK6 phosphorylates tubulins and regulates homogeneity of cortical microtubule array. NEK6 genetically interacted with microtubule-associated proteins; SPR2, GCP2/SPR3, and ARK kinesins. Especially, ARK kinesins were required for localization and activity of NEK6. The down-regulation of NEK4 compensated ibo1/nek6 mutant phenotype and the ibo1-3 mutation reduced interaction of NEK6 with NEK4. These results indicated that NEK6 controls microtubule organization and regulates anisotropic cell growth in concert with NEK4 and ARKs.
