Spatial pattern of cdc2 expression in relation to meristem activity and cell proliferation during plant development.

Abstract

The p34 protein kinase encoded by the cdc2 gene is a key component of the eukaryotic cell cycle required for the G1-to S-phase transition and entry into mitosis. To study the regulation of plant meristem activity and cell proliferation, we have examined the tissue-specific accumulation of cdc2 transcripts in Arabidopsis thlana and the related crucifer radish (Raphanus saivus) by in situ hybridization usingA. thaliana cdc2 cDNA sequences as a probe. cdc2 transcripts accumulated in leaf primordia and within the vegetative shoot apical meristem. During flower development, high levels of expression were observed in meristems, in the basal regions ofdeveloping organs, in the developing vasculature, and assocated with rib meristems elaborated late in the development ofsome floral organs. In root tips, cdc2 transcripts accumulated in the meristematic region and adjacent daughter cells but were not detected in the quiescent center. There was strong hybridization throughout the pericycle, and a further localized accumulation of cdc2 transcripts was observed in the initial stages ofthe activation ofa new meristem at sites of lateral root development. We conclude that cdc2 expression is a critical factor in the regulation of meristem activity and establishment of proliferative competence.The p34 protein kinase encoded by cdc2 is a key component of the eukaryotic cell cycle required for the Gj-to S-phase transition and entry into mitosis (1-3). p34 protein kinases become active only after forming a complex with a cyclin, and mutant analysis in Saccharomyces cerevisiae and Schizosaccharomyces pombe have demonstrated the presence of both positive regulators (e.g., cdc25+ and nim1 +) and negative regulators (e.g., wee1+) of M-phase p34 protein kinase activity (1-3). p34 protein kinases are highly conserved in evolution and have been found in all eukaryotes analyzed, including several plant species. cdc2 cDNA clones from Arabidopsis thaliana (4, 5), alfalfa (6), pea (7), and maize (8) complement cdc2 mutants in Sc. pombe or mutants in the equivalent gene (cdc28) in S. cerevisiae.Molecular cloning of plant cdc2 sequences provides the basis for mechanistic analysis of the regulation of cell proliferation in relation to the unique stem cell organization of higher plants mediating continuing organogenesis during postembryonic growth. In the present paper, we demonstrate by in situ hybridization analysis of the tissue-specific accumulation of cdc2 transcripts in A. thaliana and the related crucifer radish (Raphanus sativus) that the spatial and temporal pattern of cdc2 expression is a critical factor in regulation of meristem activity.MATERIALS AND METHODS Plant Material. A. thaliana ecotypes Columbia and Landsberg erecta were grown in the greenhouse under a 16-h light/8-h dark regimen. To isolate RNA from roots, plants were grown in liquid MS medium (9). For auxin induction, radish (cv. Scarlet Globe) seeds were surface sterilized and germinated in the dark (10). Roots were cut into 2-cm pieces and incubated in the dark at ...

Control of in vitro organogenesis by cyclin-dependent kinase activities in plants

“…This assumption is consistent with the fact that, in our assay, calli were formed in the presence of a higher concentration (2.0 g͞ml) of NAA, which might lead to an increase in CDKs transcript levels (24)(25)(26)(27). It was, however, difficult to monitor the change of CDK activity during the early phase of organogenesis because the dedifferentiation process is initiated in a single differentiated cell within the vascular bundle (28).…”

Gibberellin promotes histone H1 kinase activity and the expression of cdc2 and cyclin genes during the induction of rapid growth in deepwater rice internodes

“…Expression of both genes is induced after treatment of roots with auxin, similar to the induction of a cdc2 homologue from Arabidopsis in auxin-treated roots (Martinez et aL, 1992). Expression of a cdc2 in Arabidopsis roots and leaf protoplasts is induced by cytokinins and auxins (Hemerly et aL, 1993).…”

Isolation, Characterization, and Pericycle-Specific Transcriptome Analyses of the Novel Maize Lateral and Seminal Root Initiation Mutant rum1

“…Cyclin T2 (BAD17160.1) was up-regulated in the wild-type pericycle. Cyclins are primary regulators of the activity of cyclin-dependent kinases, which play a crucial role in controlling eukaryotic cell cycle progression (Wang et al, 1994) and are activated when quiescent cells become ready to reenter the cell cycle (Martinez et al, 1992). Lateral root initiation is such a process in which quiescent pericycle cells are activated and reenter the cell cycle.…”