Plant cell morphogenesis is constrained by the rigid extracellular matric known as the cell wall. To aquire specific form, the wall must be extended under turgor-driven growth in an assymteric fashion. This requires generation of material anisotropies in the wall. Cellulose microfibrils are the major load bearing component of the plant cell wall. They can also be thought of as scaffolding for other wall constituents such as hemicelluloses and pectins. The orientation and arrangement of cellulose microfibrils are thought to be a primary determinant of the material anistropy required to create specific cell form.

Cellulose is syntheized by a large transmembrane protein complex, with charged sugar subunits being introduced from teh cytosol, polymerized within the complex, and the product being extruded into the extracellular space. The catalytic subunit is called CESA, of hwich there are 10 isoforms in Arabidopsis. Genetic and biochemical evidence suggest that 3 CESA isforms are required to build an active complex.

Recently, we succeeded in marking and imaging cellulose synthase complexes by genetically fusing the green fluorescent protein to the N-terminus of CESA6. The tagged protein complements a loss of CES6 function, indicating that it is functional. Other groups have now tagged other CESA isoforms. These tools have made it possible to visualize individual protein complexes in living cells as they synthesize cellulose, allowing us to test longstanding hypotheses about the role o fthe cortical cytoskeleton in driving cellulose orientation, to study CESA trafficking and targeting to the plasma membrane, and to assay cellulsoe synthesis at the level of individual complexes.