1. Tissue-wide Mechanical Forces Influence the Polarity of Stomatal Stem Cells in Arabidopsis 
Martin Bringmann, Dominique C. Bergmann 
Current Biology 
Volume 27, Issue 6, Pages (March 2017)
DOI: /j.cub
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2. Current Biology 2017 27, 877-883DOI: (10.1016/j.cub.2017.01.059)
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3. Figure 1
Global Orientation of BRXL2 Crescents Depends on Leaf Type and Region
(A) Diagram of stomatal lineage cells in leaf context showing base (b), middle (m), and tip-most (t) thirds of the leaf (dashed line, midline). Protodermal cells become meristemoid mother cells (MMCs). Polar BRXL2 localization (yellow) precedes asymmetric cell division (ACD), resulting in a meristemoid (M) and a stomatal lineage ground cell (SLGC). Meristemoids can become MMCs and undergo multiple ACDs (circular arrow) before differentiation to guard cells. SLGCs differentiate into pavement cells (PCs).
(B) MMC undergoing an ACD (from Movie S1). PM, plasma membrane.
(C) Magnification of middle panel in (B). BRXL2 orientation angle α describes the angle between the leaf midline and the connection between cell center (circle) and the center of the BRXL2 subdomain (blue cross). Scale bars, 5 μm.
(D) Histogram of α in first true leaves (7 dpi, n = 1,044 cells from four individuals) left (blue bars) and right (yellow bars) of the midline.
(E) Bias in α (absolute values) at base (n = 368), middle (n = 370), and tip (n = 117), from three individuals.
(F) Histogram of α for cotyledons (4 dpi, n = 385 cells from three individuals).
See also Figure S1.
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4. Figure 2 Growth and Polarity Analysis of Leaf Epidermis
(A and B) Relative (A) and absolute (B) growth rates (6.5-dpi true leaves, 17 hr) represented as heatmaps (t0).
(C) Growth anisotropy. White bars, PDGmax for cells with anisotropy ≥15%.
(D–F) Magnified regions corresponding to boxes in (C).
(G) BRXL2 orientation (red arrows) at t0 and PDGmax (white bars) for the same cells after the growth period (t0–t17).
(H) αG describes the difference between α and PDGmax (n = 628 cells from four individuals). Scale bars, 50 (A–C) and 10 μm (D–G).
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5. Figure 3 Mechanical Perturbations Directly Influence α
(A) Ablation scheme (upper panel). αA describes BRXL2 orientation (red line) in a given cell (here, blue with yellow circle at cell center) with reference to the ablation center (white line, green circle).
(B) BRXL2-YFP in cells bordering ablation site (gray area) 16 hr after ablation.
(C) αA measured in all cells in color-coded circles in (B) (n = 175 cells from six individuals).
(D) BRXL2-YFP (yellow asterisk) localizes toward the ablation site (gray) (from Movie S2). Magenta, PM-RFP.
(E) Scheme of stretch experiments. Increasing degrees of stretch were imposed on 4-dpi cotyledons, 90° to the midline.
(F) Histograms for α at increasing stretch intensities (0%–60%) (n = 3,571 cells from ten or more individuals per stretch intensity).
(G) α in stretch direction (80°–100°).
Welch’s t test, ∗p < 0.05 and ∗∗p < 0.01; n.s., not significant. Scale bars, 10 μm (A and B) and 5 μm (D). See also Figures S2 and S3.
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6. Figure 4
Interactions among Microtubules, BRXL2, and Peptide Signals during Leaf Development
(A) Scheme of leaf blade (purple) and midvein (gray). Orientation of α (arrows) in BRXL2-expressing blade cells parallels general growth direction of midline. In atktn1 global BRXL2 orientation is randomized.
(B) α in wild-type and atktn1 (n = 447 cells from five individuals in atktn1, n = 357 cells from four individuals in wild-type).
(C–F) Images of BRXL2-YFP (C and D) and TUA5-mCherry (E and F). Ablation was immediately followed by 100-mM oryzalin treatment overnight (inset in E). BRXL2-YFP polarization and orientation relative to the ablation site is maintained (C). Mock treatments are shown in (D) and (F).
(G) Time lapse of BRXL2-YFP and TUA5mCherry shows the arrival of BRXL2 at the membrane slightly before PPB establishment. Arrowheads indicate sites of PPB establishment (magenta) and BRXL2 polarization (yellow) (Movie S3). Time stamp, hr:min.
(H) Quantification of (G). Difference in time points for first visible BRXL2 polarity and PPB formation is shown. Gray box indicates instances where BRXL2 polarity was detected first (n = 21 cells from three individuals).
(I) pEPF1::NLS-CFP expression in 7-dpi leaf.
(J) Percentage of cells expressing EPF1 in subpopulations along the proximal-distal axis (n = 4 individuals).
Scale bars, 5 μm (G) and 20 μm (C–F and I). See also Figure S4.
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