Abstract
The quiescent centre (QC) in the Arabidopsis root apical meristem is essential for stem cell organization. Here we show that the loss of REPRESSOR OF WUSCHEL1 (ROW1), a PHD domain-containing protein, leads to QC failure, defects in cell differentiation and ectopic expression of WUSCHEL-RELATED HOMEOBOX 5 (WOX5) in cells that normally express ROW1. The wox5-1/row1-3 double mutants show similar phenotypes to wox5-1 indicating that WOX5 is epistatic to ROW1. ROW1 specifically binds trimethylated histone H3 lysine 4 (H3K4me3) in the WOX5 promoter region to repress its transcription. QC expression of ROW1 results in a wox5-1-like phenotype with undetectable WOX5 transcripts. We propose that ROW1 is essential for QC maintenance and for stem cell niche development through the repression of WOX5 in the proximal meristem.
Highlights
The quiescent centre (QC) in the Arabidopsis root apical meristem is essential for stem cell organization
We expect that ectopic QC expression of mCherry-REPRESSOR OF WUSCHEL1 (ROW1) will inhibit the WUSCHEL-RELATED HOMEOBOX 5 (WOX5) promoter activity eventually, we propose that (1) a minimal amount of mCherry-ROW1 has to be present in the QC to repress the WOX5 promoter activity and (2) that mCherry[34] is more stable than the GFP, which originated from Dr5::GFP35, and that as a result, only the red mCherry red fluorescent protein (RFP), and not the green GFP signal, was observed in the QC (Fig. 4a, lower panel)
While we show that ROW1 is able to repress WOX5::GFP when ectopically expressed in the QC, deletion of the proposed ROW1-binding sites in the WOX5 promoter did not induce WOX5 expression in the proximal meristem (PM) (Supplementary Fig 6b)
Summary
The quiescent centre (QC) in the Arabidopsis root apical meristem is essential for stem cell organization. We propose that ROW1 is essential for QC maintenance and for stem cell niche development through the repression of WOX5 in the proximal meristem. OC-specific WUS transcription is required for stem cell homeostasis in the shoot apical meristem (SAM)[4,5]. The stem cell population in the root apical meristem is maintained by confining the expression of WUSCHEL-RELATED HOMEOBOX 5 (WOX5), a homeobox transcription factor[10,11] to the QC. Previous studies revealed that certain PHD domain-containing proteins bind to H3K4me[3] to regulate target gene transcription via histone acetyl transferase activities or histone deacetylase chromatin-modifying complexes[20,21,22]. We show that ROW1 is required to maintain QC identity and stem cell niche development We propose that it functions by suppressing WOX5 expression in the PM of Arabidopsis root. We believe that it is the first key repressor that maintains both root apical meristem and SAM structures by interacting with WUS and WOX5 independently
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