Developmental expression of the arabidopsis cyclin gene cyc1At

In eukaryotes, the control of cell cycle progression is exercised by heteromeric protein kinase complexes composed of a cell cycle-dependent, kinase-related subunit (Cdc2) and a cyclin subunit. To explore the possibility that cyclin transcription plays a role in the developmental regulation of cell division, we examined the spatial and temporal expression of a cyclin gene (cyc1At) in Arabidopsis. In root and shoot apical meristems and during embryogenesis, cyc1At expression is almost exclusively confined to dividing cells. A cell-specific pattern of cyc1At expression was noticed in root meristems. We examined the effects of induction of cell division of differentiated cells on cyc1At expression. During lateral root formation, induction of cyc1At expression is a very early event and was detected before anatomical modifications were visible. Treatment of roots with oryzalin, which blocks cell division in metaphase, did not inhibit the auxin induction of cyc1At, suggesting that induction of cyc1At expression precedes the completion of the first division cycle after induction of lateral roots. In tobacco protoplasts, an increase in cyc1At expression was observed only when cell division was induced. Together, the results suggest that Cyc1At accumulation in Arabidopsis is transcriptionally regulated and might be one of the limiting factors for the activation of cell division.