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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
Author(s) -
Takatsuka Hirotomo,
Ohno Ryoko,
Umeda Masaaki
Publication year - 2009
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/j.1365-313x.2009.03884.x
Subject(s) - cyclin dependent kinase , microbiology and biotechnology , biology , cyclin dependent kinase 1 , endoreduplication , kinase , phosphorylation , protein kinase a , cyclin dependent kinase 2 , arabidopsis , cell cycle , mutant , biochemistry , cell , gene
Summary 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.