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.
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.
Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara, Japan.
Hirotomo
H
Takatsuka
Ryoko
R
Ohno
Masaaki
M
Umeda
D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002455:Cell Division; D049108:Cell Enlargement; D049109:Cell Proliferation; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D055786:Gene Knockout Techniques; D016254:Mutagenesis, Insertional; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D018749:RNA, Plant / Q000235:genetics
D029681:Arabidopsis Proteins; D018749:RNA, Plant; C112244:Cak1at protein, Arabidopsis; D017346:Protein Serine-Threonine Kinases; C434472:CDKA1 protein, Arabidopsis; C514673:CDKD;2 protein, Arabidopsis; D018844:Cyclin-Dependent Kinases