Dissecting regulatory pathways of G1/S control in Arabidopsis: common and distinct targets of CYCD3;1, E2Fa and E2Fc.

Activation of E2F transcription factors at the G1-to-S phase boundary, with the resultant expression of genes needed for DNA synthesis and S-phase, is due to phosphorylation of the retinoblastoma-related (RBR) protein by cyclin D-dependent kinase (CYCD-CDK), particularly CYCD3-CDKA. Arabidopsis has three canonical E2F genes, of which E2Fa and E2Fb are proposed to encode transcriptional activators and E2Fc a repressor. Previous studies have identified genes regulated in response to high-level constitutive expression of E2Fa and of CYCD3;1, but such plants display significant phenotypic abnormalities.

Distinct light-initiated gene expression and cell cycle programs in the shoot apex and cotyledons of Arabidopsis.

In darkness, shoot apex growth is repressed, but it becomes rapidly activated by light. We show that phytochromes and cryptochromes play largely redundant roles in this derepression in Arabidopsis thaliana. We examined the light activation of transcriptional changes in a finely resolved time course, comparing the shoot apex (meristem and leaf primordia) and the cotyledon and found >5700 differentially expressed genes.

The developmental context of cell-cycle control in plants.

Plant growth is characterised both by continued growth and organogenesis throughout development, as well as by environmental influences on the rate and pattern of these processes. This necessitates a close relationship between cell cycle control, differentiation and development that can be readily observed and studied. The sequencing of the Arabidopsis genome has revealed the full complexity of cell cycle regulators in plants, creating a challenge to understand how these genes control plant growth and differentiation, and how they are integrated with intrinsic and external signals.

Global analysis of the core cell cycle regulators of Arabidopsis identifies novel genes, reveals multiple and highly specific profiles of expression and provides a coherent model for plant cell cycle control.

Arabidopsis has over 80 genes encoding conserved and plant-specific core cell cycle regulators, but in most cases neither their timing of expression in the cell cycle is known nor whether they represent redundant and/or tissue-specific functions. Here we identify novel cell cycle regulators, including new cyclin-dependent kinases related to the mammalian galactosyltransferase-associated protein kinase p58, and new classes of cyclin-like and CDK-like proteins showing strong tissue specificity of expression. We analyse expression of all cell cycle regulators in synchronized Arabidopsis cell cultures using multiple approaches including Affymetrix microarrays, massively parallel signature sequencing and real-time reverse transcriptase polymerase chain reaction, and in plant material using the results of over 320 microarray experiments.