Cellulose biosynthesis regulation

The formation of plant cellulases has been found to be closely regulated by different growth hormones, particularly auxin (6,11), steroids (12), or ethylene gas (13). The hormones act in different tissues under different circumstances, and they seldom lead to such high cellulase activity that there is a net decline in total cellulose. Indeed, cellulose biosynthesis usually continues even while partial hydrolysis occurs, and net cellulose deposition often keeps pace with growth under all of these conditions (14). 

Available evidence supports a common ancestry for all cellulose synthases. These enzymes appear to have been a bacterial invention acquired by various eukaryotes via multiple lateral gene transfers. However, the proteins associated with regulation of cellulose biosynthesis and polymer crystallization seem to have evolved independently. Sequence divergence of eukaryotic cellulose synthases and the presence of multiple gene clusters associated with bacterial cellulose synthases are discussed in relation to the possible evolutionary pathways of cellulose biosynthesis. 

Cellulose production confers bacterial cell-cell interactions, adhesion to abiotic surfaces (biofilm formation) and chlorine resistance to the organism (Romling et al. 2000 Zogaj et al. 2001 Solano et al. 2002). Beginning studies shed some light on the molecular mechanisms of cellulose biosynthesis and regulation in S. typhimurium and the epidemiology of cellulose biosynthesis in Enterobacteriaceae. 

Figure 7-2. Structure of the cellulose biosynthesis operon bcs in Salmonella typhimurium and Escherichia coli. Arrowheads represent the open reading frames (ORFs). Symbols above the ORFs show overlap of (D) or distance between (A) ORFs in bps. Symbols below the ORFs show insertions (A) or deletions (V), which occur in S. typhimurium LT2 as compared to Escherichia coli K-12. Closed arrow5 just above the ORFs indicate transposon insertions in bcsA and bcsC. The larger arrow indicates the position of the transposon used to study transcriptional regulation of the respective gene. The table summarizes the features of bcs genes using the positioning in the genome of the sequenced LT2 strain. The start codon proposed for bcsC in E. Coli K-12 leads to a shorter ORF (bcsC ).

S. typhimurium has 12 copies of this domain. That all 12 proteins with this domain are involved in the regulation of cellulose biosynthesis, but under different... 

Recently, the molecular basis of cellulose biosynthesis has been detected in S. typhimurium and other Enterobacteriaceae. With this discovery, however, new questions did arise concerning various aspects such as the mode of cellulose biosynthesis, its regulation, function, epidemiology, structure and interaction of cellulose with other components. At present, answers are only partially available, if at all. The availability of well characterized and fully sequenced strains together with efficient tools for genetic manipulation, however, gives hope that fairly soon light will be shed at least to some aspects of cellulose biosynthesis in Enterobacteriaceae. 

Model for regulation of cellulose biosynthesis in A. xylinum (reprinted from Polymer Degradation and Stability, vol. 59, E.J. Vandamme, S. De Baets, A. Vanbaelen, K. Joris and P. De Wulf, Improved production of bacterial cellulose and its application potential, 93-99, copyright (1998), with permission from Elsevier). 

The multiplicity of cellulases is of fundamental interest because of its implications on the basic understanding of cellulose hydrolysis as well as the regulation of cellulase biosynthesis. 

J. Preiss M. N. Sivak, Biosynthesis and Regulation of Planf Sfarch and Bacterial and Mammalian Glycogen Synthesis In Comprehensive Natural Products Chemistry Vol. 3, Carbohydrates and Their Derivatives Including Tannins, Cellulose and Related Lignin] B. M. Pinto, Ed. Pergamon Press Oxford, UK, 1999 pp 441-495. 

Andersson-Gunneras S., Mellerowicz E.J., Love J., Segerman B., Ohmiya Y, Coutinho P.M., Nilsson R, Henrissat B., Moritz T., and Sundberg B. 2006. Biosynthesis of cellulose-enriched tension wood in Populus global analysis of transcripts and metabolites identifles biochemical and developmental regulators in secondary wall biosynthesis. Plant J 45 144-165. 

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