FIGURE 7.

Speculative model for the stages of cellulose formation. T0, cellulose synthase complex (CSC) is targeted and integrated into the plasma membrane. T1, COBRA is recruited to the vicinity of the cellulose synthase complex. Upon activation of the cellulose synthase complex, individual β1–4-glucose chains emerge from the complex. T2, during the beginning of cellulose synthesis, the β1–4-glucose chains (in the model only 2 are drawn, for simplicity) are bound by COBRA proteins, one glucan chain by one molecule of COBRA protein. COBRA facilitates the interaction of the individual chains into a cellulose fibril. T3, if COBRA does not dissociate from the cellulose microfibrils it would eventually be found in the cell wall as newly synthesized cellulose fibrils displace older fibrils.