Tracks for cellulose

Cellulose synthase (CESA) tracks along paths coincident with microtubules, say Alex Paredez, Chris Somerville, and David Ehrhardt (Carnegie Institution, Stanford, CA). The resulting parallel cellulose fibrils constrain cell expansion so that plants elongate primarily along a single axis.

A transmembrane CESA complex takes cytoplasmic substrates and turns them into 36 extracellular glycan chains. At some distance from the complex, the extruded chains crystallize into a cellulose microfibril.

CESA's relationship to plant cortical microtubules has been difficult to determine given the microtubules' dynamic nature. Through rapid treadmilling and turnover, the microtubules bump into each other and realign, thus helping create a parallel array that is perpendicular to the axial direction of plant growth. In static pictures CESA was often nowhere near a microtubule, leading some to suggest that CESA was channeled between microtubule...