Figure 1.

Regulatory mechanism involved in root stem cell maintenance and how CLE40p delays protophloem development. A, Schematic overview of the current hypothesis of the regulation mechanism involved in root stem cell maintenance. WOX5 is synthesized in the QC and moves from there through PDs to the underlying CSCs, maintaining their fate. ACR4 and CLV1 are believed to be involved in the regulation of this movement due to their localization at the sites of PDs. CLE40p is synthesized from the differentiated CCs. Binding to the ACR4-CLV1 complex could lead to a conformational change, making WOX5 unable to move to the next cell layer, which will lead to a differentiation of the CSCs. B, Fluorescence intensity (depicted as the mean gray value in the root tip, indicated by the white outline in C), of plants expressing pSUC2:GFP under the control condition and after 1, 2, or 3 d of CLE40p treatment. Significant differences (P < 0.05), as determined by two-way ANOVA with Tukey's post hoc analysis, are indicated by lowercase letters above the bars (n ≥ 25). A.U., Arbitrary units. C, pSUC2:GFP in the root meristem under the control condition and after 1, 2, or 3 d of CLE40p (1 μm) treatment. Scale bars = 20 µm. The region outlined in white was used for fluorescence intensity measurements in B. D, pAPL:GUS marking the phloem in the root meristem under the control condition and after 1, 2, or 3 d of CLE40p (1 μm) treatment. Scale bars = 100 µm.