A Molecular Framework for the Embryonic Initiation of Shoot Meristem Stem Cells

Zhang, Zhongjuan; Tucker, Elise J.; Hermann, Marita; Laux, Thomas

doi:10.1016/j.devcel.2017.01.002

Cited by 95 publications

(94 citation statements)

References 68 publications

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“…Reduced levels of the relevant PLT, SCR, and TCP proteins in primary roots and their embryonic progenitors, regenerating roots, and LRPs reveal dose-dependent defects in the specification and activity of organizer cells within the root stem cell niche: the QC cells. Our genetic and protein interaction data indicate that dosage-sensitive combinatorial interactions among PLT-TCP-SCR directly regulate promoter activity of the WOX5 gene, which is the best-studied specific molecular marker for QC activity (Sarkar et al 2007;Pi et al 2015;Zhang et al 2017b). Consistent with this scenario, overexpressed PLTs can only effectively expand the WOX5 expression domain where SCR and TCP also are highly expressed.…”

Section: Discussionmentioning

confidence: 52%

“…During initiation of the embryonic shoot stem cells, a WOX2 module promotes the expression of HD-ZIPIII genes to ensure the appropriate ratio of cytokinin and auxin pathways (Zhang et al 2017b). During de novo shoot regeneration, cytokinin B-type Arabidopsis response regulators (ARRs) combine with HD-ZIP III coactivators for region-specific activation of the WUS promoter (Zhang et al 2017a), whereas, in the SAM, ARRs appear to maintain mainly WUS expression (Meng et al 2017;Zhang et al 2017a).…”

Section: Discussionmentioning

confidence: 99%

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Root stem cell niche organizer specification by molecular convergence of PLETHORA and SCARECROW transcription factor modules

et al. 2018

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Continuous formation of somatic tissues in plants requires functional stem cell niches where undifferentiated cells are maintained. In Arabidopsis thaliana, PLETHORA (PLT) and SCARECROW (SCR) genes are outputs of apicalbasal and radial patterning systems, and both are required for root stem cell specification and maintenance. The WUSCHEL-RELATED HOMEOBOX 5 (WOX5) gene is specifically expressed in and required for functions of a small group of root stem cell organizer cells, also called the quiescent center (QC). PLT and SCR are required for QC function, and their expression overlaps in the QC; however, how they specify the organizer has remained unknown. We show that PLT and SCR genetically and physically interact with plant-specific teosinte-branched cycloidea PCNA (TCP) transcription factors to specify the stem cell niche during embryogenesis and maintain organizer cells post-embryonically. PLT-TCP-SCR complexes converge on PLT-binding sites in the WOX5 promoter to induce expression.

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Section: Discussionmentioning

confidence: 52%

Section: Discussionmentioning

confidence: 99%

Root stem cell niche organizer specification by molecular convergence of PLETHORA and SCARECROW transcription factor modules

et al. 2018

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“…Alternatively, defective stem cell homeostasis alone could explain the lack of AM in wus mutants. Recent work on embryonic shoot stem cell initiation indicated that WUS is dispensable for stem cell initiation and that several members of the WUSCHEL-RELATED HOMEOBOX gene family redundantly function in this process in embryos (Zhang et al, 2017). It remains to be tested whether WUS is required for stem cell initiation in the AM, in addition to its role in stem cell homeostasis.…”

Section: Wus Is Required For Am Initiation and Integritymentioning

confidence: 99%

Cytokinin Signaling Activates WUSCHEL Expression during Axillary Meristem Initiation

et al. 2017

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The homeodomain transcription factor WUSCHEL (WUS) defines the shoot stem cell niche, but the mechanisms underlying the establishment of WUS expression remain unclear. Here, we show that cytokinin signaling precedes WUS expression in leaf axils and activates WUS expression de novo in the leaf axil to promote axillary meristem initiation. Furthermore, type-B Arabidopsis response regulator proteins, which are transcriptional activators in the cytokinin signaling pathway, directly bind to the WUS promoter and activate its expression. Finally, we show that cytokinin activation of WUS in the leaf axil correlates with increased histone acetylation and methylation markers associated with transcriptional activation, supporting the fact that WUS expression requires a permissive epigenetic environment to restrict it to highly defined meristematic tissues. Taken together, these findings explain how cytokinin regulates axillary meristem initiation and establish a mechanistic framework for the postembryonic establishment of the shoot stem cell niche.

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“…LEAFY COTYLEDON1 (LEC1) is a central regulator of seed development, and marks zygotic embryos during normal development (Lotan et al, 1998). WUSCHEL RELATED HOMEOBOX 2 (WOX2) plays a role in initiating shoot meristem stem cells in embryos (Zhang et al, 2017). Its expression starts in the fertilized egg and is localized in the apical half of the embryo after asymmetric cell division (Ueda et al, 2011).…”

Section: Expression Pattern Of Embryonic Markers and Selection Of Se-mentioning

confidence: 99%

Characterization of somatic embryogenesis initiated from the Arabidopsis shoot apex

Kadokura

Sugimoto

Tarr

et al. 2018

Developmental Biology

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Somatic embryogenesis is one of the best examples of the remarkable developmental plasticity of plants, in which committed somatic cells can dedifferentiate and acquire the ability to form an embryo and regenerate an entire plant. In Arabidopsis thaliana, the shoot apices of young seedlings have been reported as an alternative tissue source for somatic embryos (SEs) besides the widely studied zygotic embryos taken from siliques.Although SE induction from shoots demonstrates the plasticity of plants more clearly than the embryo-to-embryo induction system, the underlying developmental and molecular mechanisms involved are unknown. Here we characterized SE formation from shoot apex explants by establishing a system for time-lapse observation of explants during SE induction. We also established a method to distinguish SE-forming and non-SE-forming explants prior to anatomical SE formation, enabling us to identify distinct transcriptome profiles of these two explants at SE initiation. We show that embryonic fate commitment takes place at day 3 of SE induction and the SE arises directly, not through callus formation, from the base of leaf primordia just beside the shoot apical meristem (SAM), where auxin accumulates and shoot-root polarity is formed. The expression domain of a couple of key developmental genes for the SAM transiently expands at this stage. Our data demonstrate that SE-forming and 3 non-SE-forming explants share mostly the same transcripts except for a limited number of embryonic genes and root genes that might trigger the SE-initiation program. Thus, SE-forming explants possess a mixed identity (SAM, root and embryo) at the time of SE specification.

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A Molecular Framework for the Embryonic Initiation of Shoot Meristem Stem Cells

Cited by 95 publications

References 68 publications

Root stem cell niche organizer specification by molecular convergence of PLETHORA and SCARECROW transcription factor modules

Root stem cell niche organizer specification by molecular convergence of PLETHORA and SCARECROW transcription factor modules

Cytokinin Signaling Activates WUSCHEL Expression during Axillary Meristem Initiation

Characterization of somatic embryogenesis initiated from the Arabidopsis shoot apex

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