Arabidopsis CYCD3 D-type cyclins link cell proliferation and endocycles and are rate-limiting for cytokinin responses

Abstract

Current understanding of the integration of cell division and expansion in the development of plant lateral organs such as leaves is limited. Cell number is established during a mitotic phase, and subsequent growth into a mature organ relies primarily on cell expansion accompanied by endocycles. Here we show that the three Arabidopsis cyclin D3 (CYCD3) genes are expressed in overlapping but distinct patterns in developing lateral organs and the shoot meristem. Triple loss-of-function mutants show that CYCD3 function is essential neither for the mitotic cell cycle nor for morphogenesis. Rather, analysis of mutant and reciprocal overexpression phenotypes shows that CYCD3 function contributes to the control of cell number in developing leaves by regulating the duration of the mitotic phase and timing of the transition to endocycles. Petals, which normally do not endoreduplicate, respond to loss of CYCD3 function with larger cells that initiate endocycles. The phytohormone cytokinin regulates cell division in the shoot meristem and developing leaves and induces CYCD3 expression. Loss of CYCD3 impairs shoot meristem function and leads to reduced cytokinin responses, including the inability to initiate shoots on callus, without affecting endogenous cytokinin levels. We conclude that CYCD3 activity is important for determining cell number in developing lateral organs and the relative contribution of the alternative processes of cell production and cell expansion to overall organ growth, as well as mediating cytokinin effects in apical growth and development.cell division ͉ cyclin D ͉ flowering time ͉ plant development

Jasmonate Controls Leaf Growth by Repressing Cell Proliferation and the Onset of Endoreduplication while Maintaining a Potential Stand-By Mode

“…The expression of CYCD3;1, and CYCD3;3 decreases during development irrespective of the genotype tested, in agreement with Beemster et al (2005). These genes have been shown to repress the switch of the mitotic cell cycle toward endocycling (Dewitte et al, 2007), and strikingly, upon MeJA treatment, their levels of expression are increased consistently in Col gl1 and aos but to a greatly reduced extent in coi1-16B (Figs. 7 and 8; Supplemental Fig.…”

“…Notably, the transcripts of D3-type cyclins, negative regulators of endoreduplication such as CYCD3;1, CYCD3;2, and CYCD3;3 (Dewitte et al, 2007), are upregulated in Col gl1 at the later time points when grown on MeJA-containing medium. The expression of CYCD3;1, and CYCD3;3 decreases during development irrespective of the genotype tested, in agreement with Beemster et al (2005).…”

“…Moreover, the switch to the endocycle requires that at least the expression of CYCD3;1 is turned off, and the triple mutant cycd3;1-3 showed premature onset of endoreduplication, indicating that the normal function of CYCD3 is to delay this (Dewitte et al, 2003(Dewitte et al, , 2007. According to current models, CYCD3;1 in complex with CDKA;1 regulates cell cycle entry by phosphorylation of RBR1, leading to the release of RBR1-bound E2F transcription factors to drive the expression of genes required for the cell cycle phase transitions (for review, see Magyar, 2008).…”

Regulating DNA Replication in Plants

“…Interestingly, SIM interacts with the CDKA;1, the canonical PSTAIRE-type CDK, and with cyclin D, implicating this cyclin not only in the G 1 /S transition but also in control of endocycles. Consistent with this, CYCD3 overexpression induces hyperplasia and reduction of the number of endoreplicated cells in various Arabidopsis organs (Dewitte et al 2003) whereas a triple cycd3;1-2-3 mutant contains reduced cell number and increased endoreplication levels (Dewitte et al 2007). CDKA/CYCD3 are responsible for the phosphorylation of RBR (RETINOBLASTOMA-RELATED), the homolog of the mammalian RB protein.…”

Desenvolvimento reprodutivo de Hyptis suaveolens (L.) Poit.: relação entre fotoperíodo, densidade celular meristemática e padrão de expressão de um ortólogo putativo do gene LEAFY de arabidopsis

“…Por outro lado, os meristemas florais não apresentaram as mesmas regiões anatômicas de um ápice vegetativo e a emissão das sépalas ocorreu após o meristema ter sofrido maior extensão longitudinal em comparação ao ápice vegetativo (figura 7). Diferenças semelhantes na morfometria entre ápices vegetativos e florais são relatadas em outras espécies, como em Arabidopsis thaliana (Dewitte et al 2007). Outra diferença reside no achatamento do meristema floral imediatamente após a emissão das sépalas (figura 7), enquanto que o ápice vegetativo adquiriu um formato cônico após a emissão dos primórdios foliares (figuras 11, 13).…”