title: The D-type cyclin CYCD3;1 is limiting for the G1-to-S-phase transition in Arabidopsis.
abstract: The G1-to-S-phase transition is a key regulatory point in the cell cycle, but the rate-limiting component in plants is unknown. Overexpression of CYCLIN D3;1 (CYCD3;1) in transgenic plants increases mitotic cycles and reduces endocycles, but its effects on cell cycle progression cannot be unambiguously determined. To analyze the cell cycle roles of plant D-type cyclins, we overexpressed CYCD3;1 in Arabidopsis thaliana cell suspension cultures. Changes in cell number and doubling time were insignificant, but cultures exhibited an increased proportion of G2- over G1-phase cells, as well as increased G2 arrest in response to stationary phase and sucrose starvation. Synchronized cultures confirm that CYCD3;1-expressing (but not CYCD2;1-expressing) cells show increased G2-phase length and delayed activation of mitotic genes such as B-type cyclins, suggesting that CYCD3;1 has a specific G1/S role. Analysis of putative cyclin-dependent kinase phosphorylation sites within CYCD3;1 shows that mutating Ser-343 to Ala enhances CYCD3;1 potency without affecting its rate of turnover and results in a fivefold increase in the level of cell death in response to sucrose removal. We conclude that CYCD3;1 dominantly drives the G1/S transition, and in sucrose-depleted cells the decline in CYCD3;1 levels leads to G1 arrest, which is overcome by ectopic CYCD3;1 expression. Ser-343 is likely a key residue in modulating CYCD3;1 activity in response to sucrose depletion.
authors.affiliation: Institute of Biotechnology, University of Cambridge, CB2 1QT Cambridge, UK.
authors.forename: Margit
authors.initials: M
authors.lastname: Menges
authors.forename: Anne K
authors.initials: AK
authors.lastname: Samland
authors.forename: Séverine
authors.initials: S
authors.lastname: Planchais
authors.forename: James A H
authors.initials: JA
authors.lastname: Murray
mesh_terms: D016590:Aphidicolin / Q000494:pharmacology; D017360:Arabidopsis / Q000166:cytology* / Q000187:drug effects; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D001483:Base Sequence; D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology*; D002460:Cell Line; D016213:Cyclins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology*; D017931:DNA Primers; D016193:G1 Phase; D016195:G2 Phase; D016297:Mutagenesis, Site-Directed; D030821:Plants, Genetically Modified; D011499:Protein Processing, Post-Translational; D016196:S Phase; D013395:Sucrose / Q000494:pharmacology
chemical_list: D029681:Arabidopsis Proteins; C511744:CYCD3;1 protein, Arabidopsis; C496944:CycD3 protein, Arabidopsis; D016213:Cyclins; D017931:DNA Primers; D016590:Aphidicolin; D013395:Sucrose