Eukaryotes, cellulose biosynthesis

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 biosynthesis is a phenomenon observed in bacteria (proteobacteria, firmicutes, and cyanobacteria) (Miihlethaler 1949 Deinema and Zevenhuizen 1971 Napoli et al. 1975 Brown, Jr. et al. 1976 Roberts 1991 Ross et al. 1991 Nobles et al. 2001 Zogaj et al. 2001, 2003 Spiers et al. 2002) and eukaryotes including plants (Glaucophyceae, Rhodophyceae, and Chlorophyceae) (Brown, Jr. 1985), animals (urochordates) (Kimura et al. 2001b), stramenopiles (Brown, Jr. 

The proliferation of complete genome sequences in public databases provides an additional means to track the evolution of cellulose in bacteria. Conservation of operons and/or gene clusters (synteny) can be used to trace not only the history of cellulose synthase, but also its associated proteins. The existence of a few these gene clusters has been well documented. In the sections below, I would like to give a brief review of the known gene organizations and introduce two novel ones which may be linked to the eukaryotic acquisition of cellulose biosynthesis. 

Current data suggest that cellulose biosynthesis is a bacterial invention and that eukaryotes acquired the process via multiple lateral gene transfers. Bacteria and eukaryota have independently evolved regulatory mechanisms and molecular structures to utilize the p-1,4-homopolymer synthesized by the catalytic activity of homologous cellulose synthase enzymes. The differences in accessory enzymes probably reflect not only convergent evolution to produce a cellulose I crystalline allomorph, but also inventions of alternative products such as cellulose II, noncrystalline cellulose, or nematic ordered cellulose. 

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