Armadillo Repeat-Containing Kinesins and a NIMA-Related Kinase Are Required for Epidermal Cell Morphogenesis in Arabidopsis

Abstract

The involvement of kinesin motor proteins in both cell tip growth and cell shape determination has been well characterized in various organisms. We have demonstrated that an armadillo repeat-containing kinesin-related protein, ARK1, is involved in root-hair morphogenesis. Microtubule polymers are more abundant in the ark1 null allele root hairs, but analysis shows that these extra microtubules are concentrated in the endoplasm, and not in the cortical array, suggesting that ARK1 regulates tip growth by limiting the assembly and distribution of endoplasmic microtubules. The ARK1 gene has two homologues, ARK2 and ARK3, and our present results show that ARK2 is involved in cell morphogenesis in the root. We further reveal that a NIMA-related protein kinase, NEK6, binds to the ARK family proteins and has pleiotropic effects upon epidermal cell morphogenesis, suggesting that NEK6 is involved in cell morphogenesis in Arabidopsis via microtubule functions associated with these armadillo repeat kinesins.