Regulation of <i>CLV3</i> Expression by Two Homeobox Genes in Arabidopsis

Brand, Ulrike; Grünewald, Margit; Hobe, Martin; Simon, Rüdiger

doi:10.1104/pp.001867

Cited by 243 publications

(234 citation statements)

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“…At present, our results cannot distinguish if downregulation of RBR or the resulting loss of cell-cell contact between L1 and L2 disrupts the CLV-WUS feedback loop, which maintains the SAM stem cell niche that contributes to meristem activity and primordia formation (Brand et al, 2000(Brand et al, , 2002Rojo et al, 2002;Tucker and Laux, 2007). Loss of CLV3 activity leads to gradual conversion of bordering cells in the SAM peripheral zone to cells with central zone characteristics , suggesting that CLV3 is involved in a signaling pathway required for the switch from stemness to differentiated cells.…”

Section: Rbr Homeostasis Is Critical For Meristem Integrity and Functionmentioning

confidence: 86%

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ArabidopsisRETINOBLASTOMA-RELATED Is Required for Stem Cell Maintenance, Cell Differentiation, and Lateral Organ Production

et al. 2010

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Several genes involved in the regulation of postembryonic organ initiation and growth have been identified. However, it remains largely unclear how developmental cues connect to the cell cycle. RETINOBLASTOMA RELATED (RBR) is a plant homolog of the tumor suppressor Retinoblastoma (pRb), which is a key regulator of the cell cycle. Using inducible RNA interference (RNAi) against Arabidopsis thaliana RBR (RBRi), we reduced RBR expression levels at different stages of plant development. Conditional reduction or loss of RBR function disrupted cell division patterns, promoted context-dependent cell proliferation, and negatively influenced establishment of cell differentiation. Several lineages of toti-and pluripotent cells, including shoot apical meristem stem cells, meristemoid mother cells, and procambial cells, failed to produce appropriately differentiated cells. Meristem activity was altered, leading to a disruption of the CLAVATA-WUSCHEL feedback loop and inhibition of lateral organ formation. Release of RBR from RNAi downregulation restored meristem activity. Gene profiling analyses soon after RBRi induction revealed that a change in RBR homeostasis is perceived as a stress, even before genes regulated by RBR-E2F become deregulated. The results establish RBR as a key cell cycle regulator required for coordination of cell division, differentiation, and cell homeostasis. INTRODUCTIONRetinoblastoma (RB) was the first tumor suppressor gene identified in animals (Friend et al., 1986) and later was associated with cell cycle regulation, thus establishing pRb as a key regulator of cell proliferation. In animals, three members of the RB family of proteins (pRb, p107, and p130), also referred to as pocket proteins (Mulligan and Jacks, 1998), negatively regulate the G1-to-S phase transition during the cell cycle. It is now widely accepted that mitogenic signals activate several cyclin-dependent kinase (CDK)-cyclin complexes during progression through G1 to phosphorylate pRb, thereby releasing it from interactions with E2F/DP transcription factor complexes to facilitate S-phase entry (Weinberg, 1995). Subsequently, pRb was also found to regulate tissue-specific transcription factors that regulate cell differentiation, such as MyoD, which activates muscle-specific genes (De Falco et al., 2006). pRb also regulates germ cell proliferation, differentiation, and survival (Toppari et al., 2003) and is required for osteoblast, keratinocyte, and macrophage differentiation (Nead et al., 1998;Liu et al., 1999;Thomas et al., 2003). Together with the tumor suppressor p53, pRb regulates adipocyte differentiation and function (Hallenborg et al., 2009). The requirement for RB in cell differentiation therefore extends beyond regulation of cell cycle entry. For example, the loss of RB function in cardioblasts affects cell differentiation by modulating the activity of cardiogenic factors (Papadimou et al., 2005).RB-related genes, termed RETINOBLASTOMA-RELATED (RBR; Ach et al., 1997), are also found in monocots (Grafi et al., 1996;Xie et al...

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Section: Rbr Homeostasis Is Critical For Meristem Integrity and Functionmentioning

confidence: 86%

“…Histological Analysis, GUS Staining, DAPI Staining, and Microscopy GUS staining was performed as described by Brand et al (2002). For histological analysis, samples were fixed in 4% formaldehyde, 50% ethanol, and 10% acetic acid overnight at 48C.…”

Section: Ploidy Analysismentioning

confidence: 99%

ArabidopsisRETINOBLASTOMA-RELATED Is Required for Stem Cell Maintenance, Cell Differentiation, and Lateral Organ Production

et al. 2010

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“…The deletions of pCLV3 were derived from the CLV3 promoter (SI Experimental Procedures) as described in an earlier study (31,35). Details on the constructs used for expression and phenotypic complementation analysis of the mutant CLV3 promoter and the misexpression of eGFP-WUS, NLS-eGFP-WUS, and Dex-inducible amiRNA for WUS silencing are given in SI Experimental Procedures.…”

Section: Methodsmentioning

confidence: 99%

Threshold-dependent transcriptional discrimination underlies stem cell homeostasis

Perales

Rodriguez

Snipes

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

125

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Transcriptional mechanisms that underlie the dose-dependent regulation of gene expression in animal development have been studied extensively. However, the mechanisms of dose-dependent transcriptional regulation in plant development have not been understood. In Arabidopsis shoot apical meristems, WUSCHEL (WUS), a stem cell-promoting transcription factor, accumulates at a higher level in the rib meristem and at a lower level in the central zone where it activates its own negative regulator, CLAVATA3 (CLV3). How WUS regulates CLV3 levels has not been understood. Here we show that WUS binds a group of cis-elements, cis-regulatory module, in the CLV3-regulatory region, with different affinities and conformations, consisting of monomers at lower concentration and as dimers at a higher level. By deleting cis elements, manipulating the WUSbinding affinity and the homodimerization threshold of cis elements, and manipulating WUS levels, we show that the same cis elements mediate both the activation and repression of CLV3 at lower and higher WUS levels, respectively. The concentrationdependent transcriptional discrimination provides a mechanistic framework to explain the regulation of CLV3 levels that is critical for stem cell homeostasis.WUSCHEL | cis-regulatory module | CLAVATA3 | shoot apical meristem | gene regulation

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“…CLV3, a secreted peptide, activates a receptor kinase pathway to restrict WUS transcription (6)(7)(8)(9). Previous studies have shown that ectopic activation of WUS in the central zone leads to meristem overproliferation (10,11). Conversely, the depletion of WUS leads to premature differentiation of stem cell progeny (11)(12)(13), showing the importance of the regulation of WUS protein levels.…”

mentioning

confidence: 99%

DNA-dependent homodimerization, sub-cellular partitioning, and protein destabilization control WUSCHEL levels and spatial patterning

Rodriguez

Perales

Snipes

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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The homeodomain transcription factor WUSCHEL (WUS) promotes stem cell maintenance in inflorescence meristems of Arabidopsis thaliana. WUS, which is synthesized in the rib meristem, migrates and accumulates at lower levels in adjacent cells. Maintenance of WUS protein levels and spatial patterning distribution is not wellunderstood. Here, we show that the last 63-aa stretch of WUS is necessary for maintaining different levels of WUS protein in the rib meristem and adjacent cells. The 63-aa region contains the following transcriptional regulatory domains: the acidic region, the WUS-box, which is conserved in WUS-related HOMEOBOX family members, and the ethylene-responsive element binding factorassociated amphiphilic repression (EAR-like) domain. Our analysis reveals that the opposing functions of WUS-box, which is required for nuclear retention, and EAR-like domain, which participates in nuclear export, are necessary to maintain higher nuclear levels of WUS in cells of the rib meristem and lower nuclear levels in adjacent cells. We also show that the N-terminal DNA binding domain, which is required for both DNA binding and homodimerization, along with the homodimerization sequence located in the central part of the protein, restricts WUS from spreading excessively and show that the homodimerization is critical for WUS function. Our analysis also reveals that a higher level of WUS outside the rib meristem leads to protein destabilization, suggesting a new tier of regulation in WUS protein regulation. Taken together our data show that processes that influence WUS protein levels and spatial distribution are highly coupled to its transcriptional activity.CLAVATA3 | feedback | homodimerization | meristem | nuclear-cytoplasmic partitioning

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Regulation of CLV3 Expression by Two Homeobox Genes in Arabidopsis

Cited by 243 publications

References 18 publications

ArabidopsisRETINOBLASTOMA-RELATED Is Required for Stem Cell Maintenance, Cell Differentiation, and Lateral Organ Production

ArabidopsisRETINOBLASTOMA-RELATED Is Required for Stem Cell Maintenance, Cell Differentiation, and Lateral Organ Production

Threshold-dependent transcriptional discrimination underlies stem cell homeostasis

DNA-dependent homodimerization, sub-cellular partitioning, and protein destabilization control WUSCHEL levels and spatial patterning

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