The Arabidopsis cyclin-dependent kinase gene cdc2bAt is preferentially expressed during S and G(2) phases of the cell cycle

Cell cycle progression is regulated by cyclin-dependent kinases (CDKs). Arabidopsis thaliana contains two cdk genes, cdc2aAt and cdc2bAt This paper compares the developmental and cell cycle phase-dependent transcription of both cdk genes. In situ hybridizations revealed that cdc2bAt steady-state mRNAs, much like cdc2aAt, are found both in meristematic cells and cells with a high proliferative competence. Cdc2aAt is expressed in every meristematic cell whereas cdc2bAt is found to be expressed in a patchy pattern. An even smaller number of meristematic cells express the mitotic cyc1At These data indicate that cdc2bAt and cyc1At mRNAs accumulate in a particular cell cycle phase in agreement with evidence provided by hybridization experiments of flow cytometry-sorted nuclei and the use of cell cycle blockers on roots. The data indicate that cdc2bAt is preferentially expressed in S and G(2) phases whereas cdc2aAt expression is constitutive throughout the cell cycle, as shown previously. The existence of two distinct CDK classes in plants is proposed: (i) constitutively expressed CDKs containing a PSTAIRE motif (e.g. cdc2aAt) and (ii) CDKs with divergent motifs which are expressed during a limited interval of the cell cycle (e.g. cdc2bAt)

Expression of CKS1At in Arabidopsis thaliana indicates a role for the protein in both the mitotic and the endoreduplication cycle

Although endoreduplication is common in plants, little is known about the mechanisms regulating this process. Here, we report the patterns of endoreduplication at the cellular level in the shoot apex of Arabidopsis thaliana L. Heynh. plants grown under short-day conditions. We show that polyploidy is developmentally established in the pith, maturing leaves, and stipules. To investigate the role of the cell cycle genes CDC2aAt, CDC2bAt, CYCB1;1, and CKS1At in the process of endoreduplication, in-situ hybridizations were performed on the vegetative shoot apices. Expression of CDC2aAt, CDC2bAt, and CYCB1;1 was restricted to mitotically dividing cells. In contrast, CKS1At expression was present in both mitotic and endoreduplicating tissues. Our data indicate that CDC2aAt, CDC2bAt, and CYCB1;1 only operate during mitotic divisions, whereas CKS1At may play a role in both the mitotic and endoreduplication cycle

Cell cycle control in Arabidopsis thaliana

The crucifer Arabidopsis thaliana is an excellent model plant to study the molecular regulation of cell division. Here, we describe the state of the art of cell cycle research in this organism. The expression of the key regulatory gene, cdc2, has been shown to be correlated with cell division and with the cellular competence to divide. Furthermore, plant hormones, such as auxins and cytokinins, have intriguing cell-specific effects on the expression of the cdc2 gene. The results are discussed in view of future developments

Cell cycle control in Arabidopsis

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