Rosette terminal complex

Schematic model of the cellulose synthase complex crystalline cellulose I emerges from the rosette terminal complex, which is embedded in the plasma membrane. View from the top (above) and the side (below). (Adopted from Perez and Mazeau [42] and from Horii [40])...

STAGES IN THE ASSEMBLY OF THE ROSETTE TERMINAL COMPLEX IN PLANTS... 

In plants, cellulose is synthesized by rosette terminal complexes (RTCs). The RTCs are hexameric protein structures containing the cellulose synthase enzyme. This enzyme synthesizes the individual cellulose chains. Each RTC is located at the interface of the cell membrane, similarly to the membrane-bound rubber transferase. Each RCT will polymerize a polysaccharide chain. This sounds a little bit complicated, but we are going to break down the synthesis into the... 

Terminal complex consolidation has also been reported in vascular plants as loosely aligned files of rosettes associated with secondary wall formation (13,14,34,35). Similar rosette files were also observed during primary wall formation in rapidly elongating regions of Avena coleoptiles... 

Cellulose synthesis takes place in terminal complexes (rosettes) in the plasma membrane. Each cellulose chain begins as a sitosterol dextrin formed inside the cell. It then flips to the outside, where the oligosaccharide portion is transferred to cellulose synthase in the rosette and is then extended. Each rosette produces 36 separate cellulose chains simultaneously and in parallel. The chains crystallize into one of the microfibrils that form the cell wall. 

Kimura, S., Laosinchai, W., Itoh, T., Cui, X., Linder, C.R., Brown, R.M., 1999. Immunogold labeling of rosette terminal ceUulose-s3fnthesizing complexes in vascular plant. Plant Cell 11, 2075-2086. 

TCs (Delmer 1999 Roberts et al. 2002), these domains are obvious candidates for playing a role in particle association in rosettes. This hypothesis is supported by the results of in vitro assays that directly implicate the zinc-binding domain in rosette assembly (Kurek et al. 2002). Terminal complex dissociation in response to cellulose synthesis inhibitors (Mizuta and Brown, Jr. 1992 Peng et al. 2001 Kiedaisch et al. 2003) suggest that the particles that compose linear and rosette TCs are held together in different ways. One of these inhibitors (AE FI 50944) is effective in organisms with rosettes, but not linear TCs (Kiedaisch et al. 2003), whereas another (dichlorobenzonitrile) disrupts the linear TCs of Vaucheria hamata (Mizuta and Brown, Jr. 1992). 

The enzymes have several putative transmembrane domains (TMD). This is consistent with previous microscopic and biochemical data indicating that cellulose synthase is an integral membrane protein and that cellulose biosynthesis occurs at the plasma membrane (Mueller and Brown, Jr. 1980 Ross et al. 1991 Brown, Jr. et al. 1996 Delmer 1999). Visible by electron microscopy, the enzymes form large linear terminal complexes in the plasma membrane of bacteria and many algae whereas they form hexagonal rosette structures in higher plants and some algae (Mueller and Brown, Jr. 1980 Ross et al. 1991 Kimura et al. 1999). Delmer (1999) has speculated that the transmembrane domains may create a... 

Bowling A.X 2005. Imaging the cytoplasmic domain of the rosette cellulose-synthesizing terminal complex. Ph.D. dissertation, The University of Texas, Austin. 

ICimura S., Laosinchai W., Itoh T, Cui X.J., Linder C.R., and Brown, Jr. R.M. 1999. Immunogold labeling of rosette terminal cellulose-synthesizing complexes in the vascular plant Vigna angularis. The Plant Cell 11 2075-2085. 

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