Plant cellulose biosynthesis module

A taxon-neutral decomposition of plant cellulose biosynthesis as a recursively decomposable module. Cellulose is synthesized at the plasma membrane by the cellulose synthase complex (CSC, the "rosette"), which polymerizes UDP-glucose into (1->4)-beta-D-glucan chains that coalesce into crystalline microfibrils in the apoplast. The module separates (1) UDP-glucose substrate supply, (2) glucan polymerization by the CSC with distinct primary- and secondary-cell-wall CESA isoform sets, (3) guidance of CSC trajectory by the cortical microtubule cytoskeleton, (4) accessory enzymes/proteins required for productive synthesis (KORRIGAN endoglucanase, COBRA), and (5) microfibril assembly and organization. It is phrased as functions, complexes, and pathway segments rather than a fixed gene list so it can represent angiosperm, grass, and (with substitution) algal implementations. Concrete UniProt members are Arabidopsis exemplars, not species-restricting claims. Cellulose synthase-like (CSL) backbones of hemicelluloses, lignin biosynthesis, and the bacterial BcsA-type machinery are out of scope. As a bioenergy module, the polymerization step and its CESA isoform composition are the principal determinants of biomass recalcitrance and the main engineering targets for improved lignocellulosic saccharification.

Identifiers are grounded only where verified against the local GO term cache or UniProt; descriptors without a `term` (e.g. UDP-glucose substrate) are deliberate rather than oversights. Representative UniProt members are concrete Arabidopsis exemplars for orientation, not exhaustive or species-restricting. In grasses (Brachypodium, Sorghum, maize) the CESA isoform numbering differs but the primary/secondary CSC distinction is conserved; mixed-linkage glucan (CSLF/CSLH) is a separate, grass-specific module.