OBE3 and WUS interaction in shoot meristem stem cell regulation

The stem cells in the shoot apical meristem (SAM) are the origin of all above ground tissues in plants. In Arabidopsis thaliana, shoot meristem stem cells are maintained by the homeobox transcription factor gene WUS (WUSCHEL) that is expressed in cells of the organizing center underneath the stem cells. In order to identify factors that operate together with WUS in stem cell maintenance, we performed an EMS mutant screen for modifiers of the hypomorphic wus-6allele. We isolated the oberon3-2 (obe3-2)mutant that enhances stem cell defects in wus-6, but does not affect the putative null allele wus-1.TheOBE3 gene encodes a PHD (Plant Homeo Domain) protein that is thought to function in chromatin regulation. Single mutants of OBE3 or its closest homolog OBE4 do not display any defects, whereas the obe3-2 obe4-2 double mutant displays broad growth defects and developmental arrest of seedlings. Transcript levels of WUS and its target gene in the stem cells, CLAVATA3, are reduced in obe3-2. On the other hand, OBE3 and OBE4 transcripts are both indirectly upregulated by ectopic WUS expression. Our results suggest a positive feedback regulation between WUS and OBE3 that contributes to shoot meristem homeostasis

Flower phenotypes of <i>obe3-2 wus-1</i>, <i>obe3-2 wus-7</i> and <i>obe3-2 wus-6</i>.

<p>Flower phenotypes of <i>obe3-2 wus-1</i>, <i>obe3-2 wus-7</i> and <i>obe3-2 wus-6</i>.</p

<i>p35S</i>:<i>cOBE3</i> expression partially suppresses <i>wus-1</i> defects.

<p>(A) Phenotypes of segregating seedlings in the progeny of a <i>p35S</i>:<i>cOBE3 wus-1/+</i> mother plant. (B) <i>p35s</i>:<i>cOBE3 wus-1</i> plants produce <i>wus-1</i>-like flowers. (C) Model for <i>WUS-OBE3</i> interaction. Scale bars: 1 mm.</p

Changes of transcripts in <i>obe3-2</i> and <i>obe4-2</i>.

<p>(A) Transcript levels of 7-day-old seedlings as indicated. Error bars represent SE. (B) After induction of <i>OBE3</i> overexpression, mRNA levels of <i>WUS</i> are increased, whereas mRNA levels of <i>CLV3</i>, <i>STM</i>, and <i>ARR7</i> are unchanged in 7-day-old seedling. Error bars represent SD. (C) <i>pWUS</i>:<i>GUS</i> expression in 6-day-old <i>obe3-1 obe4-1/+</i> seedlings is confined to the OC as in the wild type. (D) <i>WUS</i> mRNA is undetectable by <i>in situ</i> hybridization in <i>obe3-1 obe4-1/+</i> floral meristems of 30-day-old plants. (E) <i>WUS</i> overexpression upregulates <i>OBE3</i> and <i>OBE4</i> mRNA levels in 7-day-old seedlings. <i>ARR7</i> expression is used as a control. Error bars represent SD. Relative mRNA levels compared to the mock control are shown.*,p<0.05, calculated from Cp’ values; ***, p<0.001, calculated from Cp’ values.</p

<i>obe3-2</i> enhances the meristem defects of weak and intermediate <i>wus</i> alleles.

<p><i>obe3-2</i> enhances the meristem defects of weak and intermediate <i>wus</i> alleles.</p

<i>OBE3</i> gene structure and mutant phenotypes.

<p>(A) Structure of the <i>OBE3</i> gene. The upstream region used for the complementation is shown in green. (B-D) Phenotypes of the denoted genotypes of 10-day-old seedlings (B), shoots (C), and flowers (D). Scale bars: 1 mm (B, D), 2 cm (C).</p

Framework for gradual progression of cell ontogeny in the Arabidopsis root meristem

In plants, apical meristems allow continuous growth along the body axis. Within the root apical meristem, a group of slowly dividing quiescent center cells is thought to limit stem cell activity to directly neighboring cells, thus endowing them with unique properties, distinct from displaced daughters. This binary identity of the stem cells stands in apparent contradiction to the more gradual changes in cell division potential and differentiation that occur as cells move further away from the quiescent center. To address this paradox and to infer molecular organization of the root meristem, we used a whole-genome approach to determine dominant transcriptional patterns along root ontogeny zones. We found that the prevalent patterns are expressed in two opposing gradients. One is characterized by genes associated with development, the other enriched in differentiation genes. We confirmed these transcript gradients, and demonstrate that these translate to gradients in protein accumulation and gradual changes in cellular properties. We also show that gradients are genetically controlled through multiple pathways. Based on these findings, we propose that cells in the Arabidopsis root meristem gradually transition from stem cell activity toward differentiation

Publisher Correction : Transcriptome dynamics revealed by a gene expression atlas of the early Arabidopsis embryo

In the version of this Resource originally published, the author information was incorrect. Jos R. Wendrich should have had a present address: Department of Plant Biotechnology and Bioinformatics and VIB Center for Plant Systems Biology, Ghent University, Technologiepark 927, 9052 Ghent, Belgium. Mark Boekschoten and Guido J. Hooiveld should have been affiliated to the Nutrition, Metabolism and Genomics Group, Division of Human Nutrition, Wageningen University, 6708 WE Wageningen, The Netherlands. In addition, the version of Supplementary Table 5 originally published with this Resource was not the intended final version and included inaccurate citations to the display items of the Resource, and the file format and extension did not match. These errors have now been corrected in all versions of the Resource