Cell wall patterning regulates plant stem cell dynamics.

The plant cell wall regulates development through spatiotemporal modulation of its chemical and mechanical properties. Pectin methylesterification is recognized as a rheological switch controlling wall stiffness. Here, we reveal a bimodal methylesterification pattern in the shoot meristem: Mature walls exhibit high methylesterification, whereas demethylesterified pectins are deposited at new cross walls. This spatial heterogeneity is established through nuclear sequestration of PECTIN METHYLESTERASE5 (PME5) mRNA. MYB3R4-driven transcription, combined with RZ-1B/1C-mediated retention, creates a mitotically associated PME5 mRNA reservoir in the nucleus. Nuclear envelope disassembly synchronizes PME5 messenger RNA (mRNA) release with cell plate formation, enabling precise demethylesterification at division planes. Perturbation of this spatial control compromises stem cell maintenance or breaks division patterning. Our study uncovers an mRNA compartmentalization mechanism that couples stem cell dynamics with pectin modification. Editor's summary: Plant cells are wrapped in a semirigid wall that reconfigures as cells expand. The chemical and material properties of pectin, a key component of cell walls, can influence cell division. Zhu et al. found different pectin properties in new versus mature cell walls, which are controlled by pectin-modifying enzymes such as PME5. The authors established that PME5 RNA is sequestered in the nucleus by RNA-binding proteins. The PME5 messenger RNA (mRNA) is released into the cytoplasm during cytokinesis when the nuclear envelope breaks down. By spatially controlling PME5 mRNA, modification of pectin can be precisely timed to coincide with the formation of new cell division plates. —Madeleine Seale [ABSTRACT FROM AUTHOR]