Kip-Related Protein 3 Is Required for Control of Endoreduplication in the Shoot Apical Meristem and Leaves of Arabidopsis

Abstract

The cell cycle plays an important role in the development and adaptation of multicellular organisms; specifically, it allows them to optimally adjust their architecture in response to environmental changes. Kip-related proteins (KRPs) are important negative regulators of cyclin-dependent kinases (CDKs), which positively control the cell cycle during plant development. The Arabidopsis genome possesses seven KRP genes with low sequence similarity and distinct expression patterns; however, why Arabidopsis needs seven KRP genes and how these genes function in cell cycle regulation are unknown. Here, we focused on the characterization of KRP3, which was found to have unique functions in the shoot apical meristem (SAM) and leaves. KRP3 protein was localized to the SAM, including the ground meristem and vascular tissues in the ground part of the SAM and cotyledons. In addition, KRP3 protein was stabilized when treated with MG132, an inhibitor of the 26S proteasome, indicating that the protein may be regulated by 26S proteasome-mediated protein degradation. KRP3-overexpressing (KRP3 OE) transgenic plants showed reduced organ size, serrated leaves, and reduced fertility. Interestingly, the KRP3 OE transgenic plants showed a significant reduction in the size of the SAM with alterations in cell arrangement. In addition, compared to the wild type, the KRP3 OE transgenic plants had a higher DNA ploidy level in the SAM and leaves. Taken together, our data suggest that KRP3 plays important regulatory roles in the cell cycle and endoreduplication in the SAM and leaves.

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.…”

Class III compensation, represented byKRP2overexpression, depends on V-ATPase activity in proliferative cells

“…Excluding KRP4, for which overexpressing transgenic lines have not been reported, the overproduction of most other KRP genes increases the cell size in tissues with meristematic features, including the shoot apical meristem and dividing cells in young leaf primordia. 11,13,14 This increase can be achieved either by increased endocycling and/or V-ATPase activity (probably through enhanced cell wall synthesis). 12,14 To understand the contribution of these KRPs to cell size regulation, a detailed analysis considering the above processes should be performed.…”

“…11,13,14 This increase can be achieved either by increased endocycling and/or V-ATPase activity (probably through enhanced cell wall synthesis). 12,14 To understand the contribution of these KRPs to cell size regulation, a detailed analysis considering the above processes should be performed.…”

“…12 The Arabidopsis genome is known to possess 7 KRP genes with low sequence similarities and distinct expression patterns. 13 11,13,14,15 We analyzed the cellular dynamism (i.e., cell number and size) in leaf primordia from 4 d after sowing (DAS) to leaf maturity (30 DAS). 11 Interestingly, in all compensation mutants analyzed to date, the actively dividing cells were similar in size to those in wild type, excluding class III observed in KRP2 o/e, in which the size of the dividing cells was 2-fold larger than in wild type.…”

SIAMESE-RELATED1 Is Regulated Posttranslationally and Participates in Repression of Leaf Growth under Moderate Drought

“…As illustrated by the higher-order 591 krp mutants and the smr2 mutant with larger shoots (Cheng et al, 2013;Kumar et 592 al., 2015), CKI proteins restrict cell proliferation during leaf growth even under non-593 stress conditions. SMR1 is also expressed under non-stress conditions and 594 participates in the regulation of leaf and root growth, since smr1 mutants show a 595 slight increase in leaf area and root length, which is most pronounced at the cellular 596 De Veylder et al, 2001;Weinl et al, 2005;Churchman et al, 2006;Liu et al, 601 2008;Jun et al, 2013;Noir et al, 2015). An even stronger growth inhibitory 602 phenotype is observed when plants express a more stable form of SMR1.…”