Multiple A-type cyclins express sequentially during the cell cycle in Nicotiana tabacum  BY2 cells

Abstract

Four full-length and one partial cDNA clones encoding four different A-type cyclins were isolated from a tobacco S-phase-specific library. The corresponding mRNAs displayed sequential appearance and disappearance during the cell cycle of highly synchronized suspension-cultured tobacco cells. Sequence analysis showed that the plant A-type cyclins can be subdivided into three distinct structural groups that are likely to be represented in every plant species. Two of the isolated tobacco cyclins belonging to the same group were highly expressed throughout S and G 2 phases but showed different kinetics of induction at the G 1 ͞S transition. Another one belonging to a second group was induced at mid-S phase and expressed until mid-M phase. A similar expression pattern was previously reported for a tobacco cyclin belonging to the third group. This sequential expression of multiple A-type cyclins in one type of plant cells makes a clear distinction from the situation in animal cells in which only one A-type cyclin exists in a given species. Furthermore, the expression of the different A-type cyclin genes responded differently upon a block at mid-S phase by DNA synthesis inhibitors. These results suggest that the multiple A-type cyclins act at different steps of the plant cell cycle and, therefore, exert distinct functions. In contrast, the expression of B-type cyclins was restricted to a narrow window corresponding to the M phase.Our knowledge of the eukaryotic cell cycle has progressed considerably during the last few years, by the finding that protein kinases play a central role in the cell cycle. The activity of the protein kinases depends on the association between a cyclin-dependent serine͞threonine kinase (cdk) as the catalytic moiety and a cyclin as a regulatory subunit. The activity of the complexes is further regulated through phosphorylation͞dephosphorylation mechanisms and binding to inhibitors (1). In animal cells, distinct cdks associating sequentially with different cyclins determine the substrate specificity of the complexes and monitor the cell cycle transitions at the G 1 ͞S and G 2 ͞M major checkpoints (2, 3). These sequential associations result from stage-specific synthesis and degradation of the cyclins while the catalytic subunit is present throughout the cell cycle. The animal cyclins have been subdivided into mitotic (A-and B-type) and G 1 (C-, D-, and E-type) cyclins according to sequence homologies and expression patterns. While the G 1 cyclins are involved in progression through G 1 phase and at the G 1 ͞S transition, the mitotic A-and B-type cyclins are essential in progression through G 2 phase and at the G 2 ͞M transition. In addition, the A-type cyclin has also been shown to play essential functions in DNA replication during S phase (4-6).It has been recently shown that the basic components of the cell cycle machinery are similar in plants and animals (7). cdk-like cDNAs and genes have been isolated from several mono-and dicotyledonous plants and shown to share about 60% sequence ...

Cyclin-Dependent Kinase Inhibitors in Maize Endosperm and Their Potential Role in Endoreduplication

“…In Arabidopsis, there are two A1 (CYCA1;1 and CYCA1;2) and four A2 and A3 (CYCA2;1 to CYCA2;4 and CYCA3;1 to CYCA3;4) genes (Chaubet-Gigot, 2000;Vandepoele et al, 2002), and maize A-type cyclins are likely to show similar complexity. Different Arabidopsis A-type cyclins were reported to be expressed sequentially at different time points from late G1/early S-phase until mid-M-phase (Reichheld et al, 1996). Consequently, it is possible the maize A1;3-type cyclin/CDK functions during S-phase and/or the G2/M transition, as was suggested for the Medicago sativa A2-type cyclin-associated CDK (Roudier et al, 2000).…”

Benzyladenine arrests cell cycle progression in G1 phase in tobacco BY-2 cells preceding induction of cell death

“…Expression of PCNA and A3-type cyclin genes starts at the G1 phase and their expression levels reach a maximum in S phase (Reichheld et al 1996;Sekine et al 1999;Jang et al 2005); thus, we chose these two genes as markers of the G1-S transition. The accumulation of gene transcripts in control cells started at 4-6 h (PCNA) or at 6-8 h (Nicta;CycA3;3), and reached their expression peak at 10 h, when several cells entered S phase ( Figure 5B).…”

“…Similar results indicating that the levels of DNA synthesis and gene expression are uncoupled were also reported in A3-type cyclins. Reichheld et al (1995Reichheld et al ( , 1996 reported that the expression of NtcycA59 and NtcycA105 (renamed Nicta;CycA3;1 and Nicta;CycA3;2, respectively; reviewed by Hemerly et al 1999) was not N. Suda et al suppressed by the addition of aphidicolin to tobacco BY-2 cells in the stationary phase, even though DNA synthesis rates decreased. This suggests that the expression level of A3-type cyclin genes and the level of DNA synthesis are not always correlated.…”

“…Treatment at G1 induced an immediate cell cycle arrest during G1 ( Figure 5B) with the loss of the second mitotic peak ( Figure 5A). The effects of benzyladenine on the expression of four genes encoding cell cycle-related proteins (proliferating cell nuclear antigen [PCNA], A3-type cyclin [Nicta;CycA3;3], A1-type cyclin [Nicta;CycA1;1] and B1-type cyclin [Nicta;CycB1;3]), whose expression patterns are regulated by the transition of specific phases, were investigated by RT-PCR ( Figure 6) using cells synchronized at M phase and treated with 50 mM benzyladenine at 0 h (M phase) or 4 h (G1 phase), whose cell cycle transition pattern is described in Figure 5.Expression of PCNA and A3-type cyclin genes starts at the G1 phase and their expression levels reach a maximum in S phase (Reichheld et al 1996;Sekine et al 1999;Jang et al 2005); thus, we chose these two genes as markers of the G1-S transition. The accumulation of gene transcripts in control cells started at 4-6 h (PCNA) or at 6-8 h (Nicta;CycA3;3), and reached their expression peak at 10 h, when several cells entered S phase ( Figure 5B).…”

Tansley Review No. 106

“…Indeed, most key regulators of the (supposedly more distant) animal cell cycle seem to be conserved in higher plants. The occurrence of cyclins and cyclin-dependent protein kinases in higher plants similar to those found in animals is now well established (Ferreira et al, 1991(Ferreira et al, , 1994Hemerly et al, 1992 ;Reichheld et al, 1995Reichheld et al, , 1996, and retinoblastoma protein homologues (Murray, 1997 ;Murray et al, 1997 ;Huntley et al, 1997) and cdc25 homologues (Sabelli et al, 1998) have been isolated recently. Given this overall conservation of cell cycle machinery and circumstantial evidence such as the fact that in a number of cyclins the primary structure reveals signatures for post-translational modifications dependent on cAMP (analogous to cyclin D " ), the observation made by Ehsan et al (1998) demands a further search for a role for cAMP in the plant cell cycle.…”