Figure 3.

Polarized cell wall specification in plant cell differentiation. (a) Diagrams show the formation of the Casparian strip in root endodermal development. The lignin deposition site is precisely defined by a CIF1/2-SGN3-SGN1 signaling module (left). The CASP proteins, which mark the Casparian strip site, are delivered to the PM by the exocysts containing EXO70A1 to the membrane sites coincides with the PtdIns(4,5)P₂ enrichment (right). (b) Diagrams show asymmetric cell wall deformation, accumulation, and modification in stomatal differentiation. The end wall thickening of GMC predicts where the PPB (green) is placed. Central wall separation involves polarized callose and pectin degradation at the pore initiation site. A functional stomatal complex requires cell wall thickening at the central pore region and modified pectins (rigid de-esterified forms) at the two poles. The pectin hardening at the polar sites imposes cell wall stiffening and mechanical force (red arrows) for functional stomatal movement. Microtubules (green lines) guide the deposition of cellulose microfibrils (blue lines) in maturing GCs.