Figure 1. Cytokinetic defects of the Arabidopsis thaliana pi4kβ1 pi4kβ2 double mutant.

The Arabidopsis pi4kβ1 pi4kβ2 double mutant displays a growth defect and cytokinetic defects.

1. The growth phenotype of the Arabidopsis pi4kβ1 pi4kβ2 double mutant can be complemented by ectopic expression of PI4Kβ1 or PI4Kβ2 or by mCherry‐tagged PI4Kβ1 expressed from a genomic fragment. Plants shown are 1 month old. Scale bar, 10 cm.
2. The irregularities in the pattern of root epidermal cell division orientation of the pi4kβ1 pi4kβ2 double mutant are also complemented by ectopic expression of PI4Kβ variants, as shown by propidium iodide (PI) staining of 5‐day‐old roots. Arrowhead, oblique cell wall. Insets, magnifications of areas showing cell wall stubs. Scale bars, 50 μm.
3. Quantifications of cell wall stubs, oblique cell walls and root meristem size (wild type, n = 15 roots; pi4kβ1, n = 15 roots; pi4kβ2, n = 14 roots; pi4kβ1 pi4kβ2, n = 18 roots; pPI4Kβ1:PI4Kβ1, n = 14 roots, pPI4Kβ2:PI4Kβ2, n = 15 roots). n.d., not detected. Data are mean ± SD. Lowercase letters indicate a significant increase of oblique cell walls (Welch ANOVA with Games‐Howell post hoc test; P < 0.0001) or a significant reduction of root meristem size in the pi4kβ1 pi4kβ2 double mutant (one‐way ANOVA with post hoc Tukey HSD; P < 0.001).
4. Complementation of the pi4kβ1 pi4kβ2 phenotype by functional FLAG‐PI4Kβ1 expressed from the intrinsic pPI4Kβ1 or the pKNOLLE promoters, as indicated, shown for 1‐month‐old plants. Scale bar, 10 cm. Complementation with the pKNOLLE‐driven construct indicates functionality of PI4Kβ1 during cell plate formation in G2/M phase.
5. PI staining of pKNOLLE:FLAG‐PI4Kβ1 expressed in the pi4kβ1 pi4kβ2 double mutant background indicates rescue of cytokinetic defects. Arrowhead, cell wall stub in the pi4kβ1 pi4kβ2 double mutant. Scale bars, 50 μm. Further phenotypic aspects of the pKNOLLE:FLAG‐PI4Kβ1‐complemented double mutants can be seen in Appendix Fig S1.