Distinct Classes of cdc2-Related Genes Are Differentially Expressed during the Cell Division Cycle in Plants

Abstract

cdc2 and several related genes encode the catalytic subunits of cyclin-dependent kinases, which have been implicated in a number of cellular processes, including control of cell division. As a first step in exploring their function in plants, we isolated four cdc2-related genes from Antirrhinum. Two genes, cdc2a and cdc2b, encode proteins that contain a perfectly conserved PSTAIRE motif characteristic of cdc2 homologs, whereas the products of the two remaining genes, cdc2c and cdc2d, appear to represent a new subclass of proteins that have so far only been identified in plants. Transcripts of these novel genes were localized in isolated cells dispersed throughout actively dividing regions of the inflorescence. This localization is consistent with accumulation that is specific to particular phases of the cell cycle. Correlating cell labeling with nuclear condensation and double-labeling experiments using cdc2 and histone H4 as probes indicated that cdc2c transcripts accumulate during S phase as well as during the G2 and M transition, whereas cdc2d expression was specific to the G2 and M phases. All cells labeled with cdc2d also contained cdc2c label, Indicating that expression of cdc2d completely overlapped with that of cdc2c. Transcripts of cdc2a and cdc2b were detected in all cells within actively dividing regions, but at levels that were only slightly higher than those observed in nondividing areas. These transcripts did not appear to accumulate in a cell cycle-specific fashion. The genes cdc2a and cdc2b were able to partially complement a yeast cdc2 mutation, although all four genes appeared to interfere with the sizing mechanism of yeast cells. We propose that plants contain at least two classes of cdc2-related genes that differ in structure, expression, and perhaps function.

Cell Cycle Regulation of Cyclin-Dependent Kinases in Tobacco Cultivar Bright Yellow-2 Cells

“…The relationships between sequences obtained in this analysis are consistent with those obtained using other algorithms (Doonan and Fobert, 1997;Segers et al, 1998;Umeda et al, 1999). CDKB1 falls into the b1 group of plant CDKs (Segers et al, 1998;Huntley and Murray, 1999), showing closest similarity to snapdragon Cdc2c (Fobert et al, 1996), alfalfa cdc2MsD (Magyar et al, 1997), and Arabidopsis CDC2b (Hirayama et al, 1991;Imajuku et al, 1992;Segers et al, 1996).…”

“…In particular, plants contain a novel group of CDKs, which not only possess a unique cyclin-binding motif in the ␣1-helix characterized by the sequence PPTA/TLRE, but also exhibit strong transcriptional regulation during the cell cycle (Hirayama et al, 1991;Fobert et al, 1996;Segers et al, 1996;Magyar et al, 1997;Segers et al, 1998;Huntley and Murray, 1999;Mironov et al, 1999;Umeda et al, 1999). The CDK-b group has recently been divided into two distinct subgroups (Huntley and Murray, 1999;Umeda et al, 1999), CDK-b1, whose members are expressed from S-G2-M phase, and CDK-b2, which are expressed in a narrower window from G2-M (Fobert et al, 1996;Magyar et al, 1997). In contrast, genes of the CDK-a (cdc2a) group have been found to show little cell cycle regulation and in general are rather widely expressed not only in actively dividing cells but also in cells that retain the potential to resume division once given the appropriate signal (Martinez et al, 1992;Hemerly et al, 1993; for review, see Mironov et al, 1999).…”

“…A cDNA library from exponentially growing BY-2 cells was screened at low stringency with the snapdragon Amcdc2c cDNA, which encodes a CDK-b1-type CDK carrying a PPTALRE sequence (Fobert et al, 1996; see "Materials and Methods"). Twenty-four positive clones were initially obtained, and after further screening rounds two non-PSTAIRE clones were sequenced completely; one (named Nicta;CdkB1;1) was 1,173 bp in length and the other (Nicta;CdkB1;2) was 1,334 bp.…”

“…Transcripts of Arabidopsis CDC2b, snapdragon cdc2c, and alfalfa cdc2MsD are reported to be present during S-G2-M phases (Fobert et al, 1996;Segers et al, 1996;Magyar et al, 1997), whereas transcripts of snapdragon cdc2d, alfalfa cdc2MsF, and rice cdc2Os3 are only detected during G2-M (Fobert et al, 1996;Magyar et al, 1997;Umeda et al, 1999). However the abundance of the protein products of CDK-b genes has only been examined for alfalfa cdc2MsD and cdc2MsF and for rice cdc2Os3, and only in the case of the alfalfa proteins was this in a synchronized cell culture system (Magyar et al, 1997;Umeda et al, 1999).…”

“…One group contains Arabidopsis CDC2b, snapdragon (Antirrhinum majus) Cdc2c, and alfalfa (Medicago sativa) cdc2MsD, which all contain the sequence PP-TALRE and for which the name CDK-b1 subgroup has been proposed (Hirayama et al, 1991;Imajuku et al, 1992;Hirt et al, 1993;Fobert et al, 1996;Segers et al, 1996;Magyar et al, 1997;Huntley and Murray, 1999). The other subgroup named CDK-b2 contains snapdragon Cdc2d, alfalfa cdc2MsF, rice (Oryza sativa) Cdc2Os3, and Arabidopsis Cdc2dAt (Hirt et al, 1993;Kidou et al, 1994;Fobert et al, 1996;Magyar et al, 1997;Umeda et al, 1999;Huntley and Murray, 1999). The CDK-b2 group CDKs have the sequence P(S/P)TTLRE with the exception of Cdc2Os3, which has PPTALRE.…”