Unknown,Transcriptomics,Genomics,Proteomics

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Differential regulation of meristem size, morphology and organization by the ERECTA, CLAVATA and class III HD-ZIP pathways

ABSTRACT: The shoot apical meristem (SAM) of angiosperm plants is a highly organized minute structure that gives rise to all above-ground organs. The SAM is divided into three different functional domains. The central zone (CZ) at the SAM tip harbors the self-renewing pluripotent stem cells and the organizing center, providing daughter cells that are continuously displaced into the interior rib zone (RZ) or to the surrounding peripheral zone (PZ), from which organ primordia are initiated. Despite the constant flow of cells from the CZ into the RZ or PZ, and cell recruitment for primordium formation, a stable balance is maintained between the distinct cell populations in the SAM. Here we combined an in depth phenotypic analysis with a comparative RNA-Seq approach to characterize meristems from selected combinations ofÂ clavata3 (clv3),Â jabba-1DÂ (jba1D) andÂ erecta (er) mutants. We demonstrate that CLV3 restricts meristem expansion along the apical basal axis, while class III HD-ZIP and ER pathways restrict meristem expansion laterally, but in distinct and possibly perpendicular orientations. OurÂ k-means analysis reveals thatÂ clv3,Â jba-1D/+ andÂ erÂ lead to meristem enlargement by affecting different aspects of meristem function, e.g., thatÂ clv3Â displays increase in stem cell population, whereasÂ jba-1D/+Â er exhibits increase in mitotic activity and in meristematic cell population. We demonstrate that thecombination of genetic and mRNA-Seq comparative approach provides a precise and sensitive method to identify cell type specific transcriptomes in a small structure such as the SAM. Ten samples enriched in shoot apical meristem tissue were analyzed, corresponding to 5 different genotypes (Col-0, clv3-2, jba-1D/+, jba-1D/+ er-20, and jba-1D/+ er-20 clv3-2) at two different developmental stages (8-day-old seedlings and 15-day-old seedlings).

ORGANISM(S): Arabidopsis thaliana

SUBMITTER: HÃ©ctor Candela

PROVIDER: E-GEOD-79839 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Cell-cell communication is critical for stem cell maintenance. Shoot apical meristem (SAM) located at the shoot tip harbors stem cells within the central zone (CZ). Their progeny differentiate in the adjacent peripheral zone (PZ). WUSCHEL (WUS) is a homeodomain transcription factor produced in a few cells of the organizing center (OC), located beneath the CZ. It has been shown to specify stem cell fate and also activate CLAVATA3 (CLV3) expression in cells of the CZ. CLV3 is a secreted peptide that activates a membrane bound receptor kinase-CLAVATA1 to restrict WUS transcription to the OC. It has been hypothesized that WUS activates CLV3 expression and stem cell fate in adjacent cells of the CZ by activating a non-cell autonomous signal. Contrary to this hypothesis, here we show that the WUS protein after being synthesized in cells of the OC, migrates into the superficial cell layers of the CZ where it activates CLV3 transcription by binding to its promoter elements. WUS also migrates laterally into the PZ to repress the expression of differentiation promoting transcription factors by binding to their regulatory regions. Migration of a stem cell inducing transcription factor into adjacent cells to activate a negative regulator, whereby restricting its own accumulation is unique to plant stem cell niches. While stem cell promoting transcription factor directly repressing differentiation promoting transcription factors to prevent premature differentiation of stem cell progenitors is conserved among diverse stem cell niches. A dexamethasone inducible version of WUSCHEL was used to identify its direct tragets. To analyze WUS-regulated gene expression programs at a higher spatial resolution, we introduced a dexamethasone (Dex)-inducible form of WUS consisting of the WUS protein-coding region fused to sequences coding for the ligand-binding domain of the rat glucocorticoid receptor (GR), expressed under a ubiquitous promoter (35S::WUS-GR) into apetala1-1;cauliflower1-1 (ap1-1;cal1-1) double mutant background. 35S::WUS-GR; ap1-1;cal1-1 SAMs were either treated with 10μM Dex or mock solution for four hours and RNA samples were hybridized to Arabidopsis ATH1 gene Chip (Affymmetrix). To identify putative genes that are directly regulated by WUS, in independent experiments, SAMs were simultaneously treated with 10μM Dex and 10μM Cycloheximide (Cyc), protein synthesis inhibitor and Cyc alone for four hours. A comparison of Dex-treated samples with mock identified 641 genes as differentially expressed [DEGs] (≥/≤2 fold; p < 0.01) and comparison of Dex+Cyc with Cyc identified 457 genes as DEGs (≥/≤2 fold; p < 0.01).

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Differential regulation of meristem size, morphology and organization by the ERECTA, CLAVATA and class III HD-ZIP pathways

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