CSLD5-mediated cell wall remodelling regulates tissue mechanics and shoot meristem growth.

New tissues and organs in plants develop from stem cells located in meristematic tissues. Cell wall-mediated mechanics has been proposed to play crucial roles in controlling stem cell activity. Here, we show that in Arabidopsis shoot apical meristems (SAMs) Cellulose Synthase Like-D5 (CSLD5)-mediated cell wall synthesis modulates tissue mechanics. The Myb-domain transcription factor MYB3R4 directly activates CSLD5 expression, leading to robust new cell wall synthesis in dividing cells. CSLD5 forms complexes with CESAs to guide cellulose-based wall construction. Disruption of CSLD5 results in reduced wall stiffness and altered expression of touch-responsive genes. Confining CSLD5 to L1 layer cells restores the mechanical properties and growth defects of csld5 SAMs, indicating molecular and cellular compensation across shoot meristem layers. We further demonstrate that epidermal expression of OsCSLD4 in rice enhances inflorescence meristem growth and seed production. Our results suggest a principle for breeding high yield crops through cell-type specific cell wall remodelling.