Multiple Functions of Kip-Related Protein5 Connect Endoreduplication and Cell Elongation  

Abstract

Despite considerable progress in our knowledge regarding the cell cycle inhibitor of the Kip-related protein (KRP) family in plants, less is known about the coordination of endoreduplication and cell differentiation. In animals, the role of cyclindependent kinase (CDK) inhibitors as multifunctional factors coordinating cell cycle regulation and cell differentiation is well documented and involves not only the inhibition of CDK/cyclin complexes but also other mechanisms, among them the regulation of transcription. Interestingly, several plant KRPs have a punctuated distribution in the nucleus, suggesting that they are associated with heterochromatin. Here, one of these chromatin-bound KRPs, KRP5, has been studied in Arabidopsis (Arabidopsis thaliana). KRP5 is expressed in endoreduplicating cells, and loss of KRP5 function decreases endoreduplication, indicating that KRP5 is a positive regulator of endoreduplication. This regulation relies on several mechanisms: in addition to its role in cyclin/CDK kinase inhibition previously described, chromatin immunoprecipitation sequencing data combined with transcript quantification provide evidence that KRP5 regulates the transcription of genes involved in cell wall organization. Furthermore, KRP5 overexpression increases chromocenter decondensation and endoreduplication in the Arabidopsis trithoraxrelated protein5 (atxr5) atxr6 double mutant, which is deficient for the deposition of heterochromatin marks. Hence, KRP5 could bind chromatin to coordinately control endoreduplication and chromatin structure and allow the expression of genes required for cell elongation.

DNA hypomethylation induces a DNA replication-associated cell cycle arrest to block hepatic outgrowth in uhrf1 mutant zebrafish embryos

“…There is close coordination between DNA methylation, chromatin structure, DNA synthesis and replication timing. DNA replication origins fire first from euchromatin, and heterochromatin protects against re-firing ( Dorn and Cook, 2011), as shown in Arabidopsis thaliana, where the maintenance of heterochromatin protects against re-replication (Jacob et al, 2010;Stroud et al, 2012) and possibly even endoreplication (Jegu et al, 2013). Thus, loss of Uhrf1 may alleviate a block to DNA re-replication, causing uncoordinated replication.…”

The Cyclin-Dependent Kinase Inhibitor KRP6 Induces Mitosis and Impairs Cytokinesis in Giant Cells Induced by Plant-Parasitic Nematodes in Arabidopsis

“…Low KRP2 levels increase DNA content, while high levels decrease DNA content (Verkest et al, 2005b;Weinl et al, 2005). Sequence alignment and specific temporal and spatial expression patterns during cell cycle progression and plant development (Menges and Murray, 2002;Ormenese et al, 2004;Menges et al, 2005) point to a functional difference among the various members of the KRP family (Kim et al, 2008;Jégu et al, 2013;Jun et al, 2013;Wen et al, 2013). Recently, KRPs have been linked to different physiological processes.…”

SWP73 Subunits of Arabidopsis SWI/SNF Chromatin Remodeling Complexes Play Distinct Roles in Leaf and Flower Development

“…Expression of SWP73B responds to UV-B treatment (Campi et al, 2012) and its RNA interference (RNAi) silencing results in dwarfism (Crane and Gelvin, 2007). SWP73B was identified as an interacting partner of cyclin-dependent kinase inhibitor KRP5 (KIP-RELATED PROTEIN5), suggesting a role in controlling the cell cycle and endoreduplication (Jégu et al, 2013). Association of SWI/SNF subunits SWI3C, SWI3D, and SWP73B with AN-GUSTIFOLIA3 (AN3), recruitment of SWP73B to promoters of AN3-regulated target genes GROWTH-REGULATING FACTOR3 (GRF3), GRF5, HECATE1 (HEC1), CONSTANS-LIKE5 (COL5), CYTOKININ RESPONSE FACTOR2 (CRF2), and RESPONSE REGULATOR4, and altered expression of these genes in the brahma (brm) SNF2-ATPase mutant suggest an important role of SWI/SNF complexes in the regulation of leaf development (Vercruyssen et al, 2014).…”