222. Saxena, I.M. and R.M. Brown, Jr. 2007 A Perspective on the Assembly of Cellulose-Synthesizing Complexes: Possible Role of KORRIGAN and Microtubules in Cellulose Synthesis in Plants. In Cellulose: Molecular and Structural Biology. Springer pp 169-181.

222. Abstract:

Cellulose is synthesized on the plasma membrane by protein complexes referred to as terminal complexes (TCs). In plants, the TCs are visualized by freeze-fracture electron microscopy as rosettes with a sixfold symmetry. Each rosette synthesizes a cellulose microfibril containing approximately 36 glucan chains. So far, only the cellulose synthase catalytic subunit (CesA) is shown to be localized to the rosette complex, and it is suggested that at least 36 CesA molecules are present in each rosette. Moreover, from analysis of the CesA genes, it is predicted that at least three different CesAs are required for assembly of the rosette and the cellulose microfibril. How the different CesA subunits assemble into a rosette structure is not clearly understood. In our view, the assembly of the rosette proceeds in stages, beginning from the rough endoplasmic reticulum (ER) to the plasma membrane, with the final assembly of the rosette structure taking place on the plasma membrane. The membrane-localized endo-l,4-(3-o-glucanase, KORRIGAN is probably involved in digesting the noncrystalline cellulose product formed from an assembly of six CesA subunits that compose a rosette particle and is transported to the plasma membrane via vesicles. These rosette particles then assemble into a complete rosette TC in the plasma membrane when the glucan chains synthesized from closely placed particles associate to form crystalline cellulose I microfibrils. The role of microtubules in aligning cellulose microfibrils has been widely debated, and we believe that microtubules probably are involved in aligning the cellulose microfibrils in an indirect manner by "channelizing" the direction of microfibril assembly.

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