ABSTRACT
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 cytometrysorted nuclei and the use of cell cycle blockers on roots. The data indicate that cdc2bAt is preferentially expressed in S and G2 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).
Subject(s)
Arabidopsis/genetics , CDC2 Protein Kinase/biosynthesis , Cyclin-Dependent Kinases/biosynthesis , Genes, Plant , Interphase/genetics , Isoenzymes/biosynthesis , CDC2 Protein Kinase/classification , Cells, Cultured , Cloning, Molecular , Darkness , Flow Cytometry , G2 Phase/genetics , Gene Expression , Growth Inhibitors/pharmacology , In Situ Hybridization , Isoenzymes/classification , Light , Polymerase Chain Reaction , RNA, Messenger/isolation & purification , RNA, Plant/isolation & purification , S Phase/genetics , Tissue DistributionABSTRACT
A system of one-shot induction of flowering in Arabidopsis thaliana, ecotype Columbia, is described. Plants from vernalized seeds are grown for 2 months in 8 h short days at an irradiance of 48 mumol m-2 sec-1 (fluorescent light only). At that age they can be induced to flower by exposure to either a single long day or a single displaced short day. Non-induced plants stay vegetative for at least a further month. Synchrony of induction among the individuals of the population exposed to one long day is of the same order as in the best classical model plants, that is, the fastest individuals are only 6 h ahead of the slowest ones. A further advantage of this system is the large size of plants at the time of induction, allowing easy analysis of changes in leaves, leaf exudate and shoot meristem. The design of such a synchronous system will allow the timings of gene activations and deactivations to be established in the different plant parts, before flowers are initiated.
