Ectopic Expression of <i>WUS</i> in Hypocotyl Promotes Cell Division via <i>GRP23</i> in <i>Arabidopsis</i>

<div><p>WUSCHEL (WUS) is essential for preventing stem cell differentiation in <i>Arabidopsis</i>. Here we report that in addition to its functions in meristematic stem cell maintenance, WUS is involved in the regulation of cell division. The <i>WUS</i> gain-of-function mutant, stem ectopic flowers (sef), displayed elongated hypocotyls, whereas the loss-of-function <i>wus-1</i> mutant had shortened hypocotyls. The long hypocotyl in <i>sef</i> was due to the presence of more cells, rather than increased cell elongation. Microscopic observation, flow cytometry assays, quantitative RT-PCR (qRT-PCR), and histochemical staining of <i>CycB1;1::GUS</i> supported the hypothesis that ectopic cell division occurred in the <i>sef</i> hypocotyls after germination. Both immunoblot and qRT-PCR results showed that <i>WUS</i> was ectopically expressed in <i>sef</i> hypocotyls. Luciferase activity, chromatin immunoprecipitation (ChIP) and electrophoretic mobility shift assay (EMSA) showed that <i>GLUTAMINE-RICH</i> PROTEIN <i>23</i> (<i>GRP23</i>) expression can be activated by WUS and that <i>GRP23</i> is a direct target gene of WUS. The phenotypes of <i>35S::GRP23</i> plants and <i>GRP23</i> knockdown lines supported the notion that <i>GRP23</i> mediates the effects of <i>WUS</i> on hypocotyl length. Together, our data suggest that ectopic expression of <i>WUS</i> in hypocotyl controls cell division through its target gene <i>GRP23</i>.</p>