Ben-Nissan Gili, Cui Weier, Kim Dong-Jin, Yang Yaodong, Yoo Byung-Chun, Lee Jung-Youn
Department of Plant and Soil Sciences, Delaware Biotechnology Institute, University of Delaware, Newark, Delaware 19711, USA.
Plant Physiol. 2008 Dec;148(4):1897-907. doi: 10.1104/pp.108.129346. Epub 2008 Oct 22.
Members of the casein kinase 1 (CK1) family are evolutionarily conserved eukaryotic protein kinases that are involved in various cellular, physiological, and developmental processes in yeast and metazoans, but the biological roles of CK1 members in plants are not well understood. Here, we report that an Arabidopsis (Arabidopsis thaliana) CK1 member named casein kinase 1-like 6 (CKL6) associates with cortical microtubules in vivo and phosphorylates tubulins in vitro. The unique C-terminal domain of CKL6 was shown to contain the signal that allows localization of CKL6 to the cortical microtubules. This domain on its own was sufficient to associate with microtubules in vivo and to bind tubulins in vitro. CKL6 was able to phosphorylate soluble tubulins as well as microtubule polymers, and its endogenous activity was found to associate with a tubulin-enriched subcellular fraction. Two major in vitro phosphorylation sites were mapped to serine-413 and serine-420 of tubulin beta. Ectopic expression of wild-type CKL6 or a kinase-inactive mutant form induced alterations in cortical microtubule organization and anisotropic cell expansion. Collectively, these results demonstrate that CKL6 is a protein kinase containing a novel tubulin-binding domain and plays a role in anisotropic cell growth and shape formation in Arabidopsis through the regulation of microtubule organization, possibly through the phosphorylation of tubulins.
酪蛋白激酶1（CK1）家族成员是进化上保守的真核蛋白激酶，参与酵母和后生动物的各种细胞、生理和发育过程，但CK1成员在植物中的生物学作用尚不清楚。在此，我们报道一种名为酪蛋白激酶1样6（CKL6）的拟南芥CK1成员在体内与皮层微管相关联，并在体外使微管蛋白磷酸化。CKL6独特的C末端结构域显示含有使CKL6定位于皮层微管的信号。该结构域本身足以在体内与微管相关联，并在体外结合微管蛋白。CKL6能够使可溶性微管蛋白以及微管聚合物磷酸化，并且发现其内源活性与富含微管蛋白的亚细胞组分相关。两个主要的体外磷酸化位点被定位到微管蛋白β的丝氨酸-413和丝氨酸-420。野生型CKL6或激酶失活突变体形式的异位表达诱导了皮层微管组织和各向异性细胞扩展的改变。总的来说，这些结果表明CKL6是一种含有新型微管蛋白结合结构域的蛋白激酶，并通过调节微管组织，可能通过微管蛋白的磷酸化，在拟南芥的各向异性细胞生长和形状形成中发挥作用。
