The Arabidopsis cyclin-dependent kinase-activating kinase CDKF;1 is a major regulator of cell proliferation and cell expansion but is dispensable for CDKA activation.
The Arabidopsis cyclin-dependent kinase-activating kinase CDKF;1 is a major regulator of cell proliferation and cell expansion but is dispensable for CDKA activation.
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DOI：
10.1111/j.1365-313x.2009.03884.x
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发表时间：
2009-08
期刊：
影响因子：
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通讯作者：
Hirotomo Takatsuka;R. Ohno;M. Umeda
中科院分区：
文献类型：
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作者：
Hirotomo Takatsuka;R. Ohno;M. Umeda
细胞周期蛋白依赖性激酶（Cyclin-dependent kinases，CDKs）在多种生物体的胚胎和胚后发育过程中的细胞周期调控中起着重要作用。CDK的完全激活不仅需要与细胞周期蛋白结合，还需要T环结构域的磷酸化。这种磷酸化由CDK激活激酶（CAK）催化。植物有两种不同类型的CAK，即CDKD和CDKF;在拟南芥中，CDKF;1在体外表现出最高的CDK激酶活性。我们先前已经表明，CDKF;1也在通过T环磷酸化激活CDKD;2和CDKD;3中起作用。在这里，我们分离了CDKF;1的敲除突变体，并表明它们在细胞分裂，细胞伸长和核内复制方面存在严重缺陷。在胚胎发生过程中没有观察到缺陷，表明CDKF;1功能主要是胚胎后发育所需的。在CDKF中; 1突变体，CDKA的T-环磷酸化;1，酵母Cdc 2/Cdc 28 p的直向同源物，与野生型植物中的相当，并且其激酶活性没有降低。相反，突变体中CDKD;2的蛋白水平和激酶活性显著降低。用不可磷酸化的丙氨酸残基取代苏氨酸-168使得CDKD;2在拟南芥组织中不稳定。这些结果表明，CDKF;1是CDKA;1活化的抑制剂，但对于维持CDKD;2的稳态水平是必不可少的，从而表明脊椎动物型CAK以植物特异性方式的定量调节。
Cyclin-dependent kinases (CDKs) play an essential role in cell cycle regulation during the embryonic and post-embryonic development of various organisms. Full activation of CDKs requires not only binding to cyclins but also phosphorylation of the T-loop domain. This phosphorylation is catalysed by CDK-activating kinases (CAKs). Plants have two distinct types of CAKs, namely CDKD and CDKF; in Arabidopsis, CDKF;1 exhibits the highest CDK kinase activity in vitro. We have previously shown that CDKF;1 also functions in the activation of CDKD;2 and CDKD;3 by T-loop phosphorylation. Here, we isolated the knockout mutants of CDKF;1 and showed that they had severe defects in cell division, cell elongation and endoreduplication. No defect was observed during embryogenesis, suggesting that CDKF;1 function is primarily required for post-embryonic development. In the cdkf;1 mutants, T-loop phosphorylation of CDKA;1, an orthologue of yeast Cdc2/Cdc28p, was comparable to that in wild-type plants, and its kinase activity did not decrease. In contrast, the protein level and kinase activity of CDKD;2 were significantly reduced in the mutants. Substitution of threonine-168 with a non-phosphorylatable alanine residue made CDKD;2 unstable in Arabidopsis tissues. These results indicate that CDKF;1 is dispensable for CDKA;1 activation but is essential for maintaining a steady-state level of CDKD;2, thereby suggesting the quantitative regulation of a vertebrate-type CAK in a plant-specific manner.