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Termination of asymmetric cell division and differentiation of stomata. Nature

Department of Biology, University of Washington, Seattle, Washington 98195, USA.
Nature (Impact Factor: 42.35). 03/2007; 445(7127):501-5. DOI: 10.1038/nature05467
Source: PubMed

ABSTRACT Stomata consist of a pair of guard cells that mediate gas and water-vapour exchange between plants and the atmosphere. Stomatal precursor cells-meristemoids-possess a transient stem-cell-like property and undergo several rounds of asymmetric divisions before further differentiation. Here we report that the Arabidopsis thaliana basic helix-loop-helix (bHLH) protein MUTE is a key switch for meristemoid fate transition. In the absence of MUTE, meristemoids abort after excessive asymmetric divisions and fail to differentiate stomata. Constitutive overexpression of MUTE directs the entire epidermis to adopt guard cell identity. MUTE has two paralogues: FAMA, a regulator of guard cell morphogenesis, and SPEECHLESS (SPCH). We show that SPCH directs the first asymmetric division that initiates stomatal lineage. Together, SPCH, MUTE and FAMA bHLH proteins control stomatal development at three consecutive steps: initiation, meristemoid differentiation and guard cell morphogenesis. Our findings highlight the roles of closely related bHLHs in cell type differentiation in plants and animals.

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    • "Likewise, the 'master regulator' activities of SPCH and MUTE have made it appealing to consider them as segregated determinants, but the details of their expression patterns make this unlikely. When SPCH or MUTE expressing cells divide, both daughters inherit maternal proteins; it is differential maintenance of the proteins that distinguish the daughters (MacAlister et al., 2007; Pillitteri et al., 2007, 2008; Lampard et al., 2008; Robinson et al., 2011). Other examples of intrinsic control can be hypothesized based on available data. "
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    • "For example, the loss of TMM or YODA function results in the production of excess stomata in contact. Three basic helix-loop-helix (bHLH) transcription factors, SPEECHLESS (SPCH), MUTE, and FAMA, are required for successive stages of development including lineage initiation and proliferation, as well as terminal differentiation (Ohashi-Ito and Bergmann, 2006; MacAlister et al., 2007; Pillitteri et al., 2007). "
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    ABSTRACT: The initiation of stomatal lineage and subsequent asymmetric divisions in Arabidopsis require the activity of the basic helix-loop-helix transcription factor SPEECHLESS (SPCH). It has been shown that SPCH controls entry into the stomatal lineage as a substrate either of the MITOGEN-ACTIVATED PROTEIN KINASE (MAPK) cascade or GSK3-like kinase BRASSINOSTEROID INSENSITIVE 2 (BIN2). Here we show that three serine residues of SPCH appear to be the primary phosphorylation targets of Cyclin-Dependent Kinases A;1 (CDKA;1) in vitro, and among them Serine 186 plays a crucial role in stomatal formation. Expression of an SPCH construct harboring a mutation that results in phosphorylation deficiencies on Serine 186 residue failed to rescue stomatal defects in spch null mutants. Expression of a phosphorylation-mimic mutant SPCH(S186D) complemented stomatal production defects in the transgenic lines harboring the targeted expression of dominant-negative CDKA;1.N146. Therefore, in addition to MAPK- and BIN2-mediated phosphorylation on SPCH, phosphorylation at Serine 186 is positively required for SPCH function in regulating stomatal development. Copyright © 2015 The Author. Published by Elsevier Inc. All rights reserved.
    Molecular Plant 12/2014; 8(5). DOI:10.1016/j.molp.2014.12.014 · 6.61 Impact Factor
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    • "This signaling pathway is parallel to that of TMM, but upstream of the basic-helix–loop–helix transcription factor SPEECHLESS (SPCH; Kang et al., 2009; Figure 2). SPCH, MUTE, and FAMA are key regulators that direct three successive stages of stomatal development (Ohashi-Ito and Bergmann, 2006; MacAlister et al., 2007; Pillitteri et al., 2007 "
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    ABSTRACT: Stomata are two-celled valves that control epidermal pores whose opening and spacing optimizes shoot-atmosphere gas exchange. Arabidopsis stomatal formation involves at least one asymmetric division and one symmetric division. Stomatal formation and patterning are regulated by the frequency and placement of asymmetric divisions. This model system has already led to significant advances in developmental biology, such as the regulation of cell fate, division, differentiation, and patterning. Over the last 30 years, stomatal development has been found to be controlled by numerous intrinsic genetic and environmental factors. This mini review focuses on the signaling involved in stomatal initiation and in divisions in the cell lineage.
    Frontiers in Plant Science 06/2014; 5:297. DOI:10.3389/fpls.2014.00297 · 3.95 Impact Factor
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