Plant growth and morphogenesis are largely driven by changes in cell walls. However, the contribution of cellulose, a key structural component of plant cell walls, to plant morphogenesis is poorly understood. Arun Sampathkumar and colleagues now address the role of cellulose in growth using mutants of three different cellulose synthases (CESAs): CESA1 and CESA3, which are highly expressed in the shoot apical meristem (SAM), as well as CESA6, a moderately expressed gene. They reveal that point mutants of CESA1 (any1) and CESA3 (cev1), but not a CESA6 null mutant (prc1-1), exhibit an increase in SAM curvature with smaller SAMs than those of wild-type plants, owing to a reduction of cell number in the SAM. Furthermore, all cesa mutants display decreased cell wall stiffness at the SAM. The authors also studied the orientation of microtubules, an important factor in relaying mechanical information and guiding structure for cellulose synthesis. They report that disruption of cellulose with cellulase or isoxaben, or the cev1 mutation, influences microtubule organisation. Lastly, the authors show that the auxin carrier protein PIN1 is less abundant in cev1 mutant SAMs, and that any1 and cev1 mutations lead to slow cell cycle progression in SAMs. Thus, cellulose is crucial for the proper growth of SAMs and impacts hormonal and cell cycle-mediated control of SAM size.
