MBE Advance Access originally published online on February 9, 2005
Molecular Biology and Evolution 2005 22(5):1273-1284; doi:10.1093/molbev/msi107
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Research Article |
Ancient Origin of Glycosyl Hydrolase Family 9 Cellulase Genes
* Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom; and Institute of Genetics, University of Nottingham, Nottingham, United Kingdom
E-mail: angus.davison{at}nottingham.ac.uk.
While it is widely accepted that most animals (Metazoa) do not have endogenous cellulases, relying instead on intestinal symbionts for cellulose digestion, the glycosyl hydrolase family 9 (GHF9) cellulases found in the genomes of termites, abalone, and sea squirts could be an exception. Using information from expressed sequence tags, we show that GHF9 genes (subgroup E2) are widespread in Metazoa because at least 11 classes in five phyla have expressed GHF9 cellulases. We also demonstrate that eukaryotic GHF9 gene families are ancient, forming distinct monophyletic groups in plants and animals. As several intron positions are also conserved between four metazoan phyla then, contrary to the still widespread belief that cellulases were horizontally transferred to animals relatively recently, GHF9 genes must derive from an ancient ancestor. We also found that sequences isolated from the same animal phylum tend to group together, and in some deuterostomes, GHF9 genes are characterized by substitutions in catalytically important sites. Several paralogous subfamilies of GHF9 can be identified in plants, and genes from primitive species tend to arise basally to angiosperm representatives. In contrast, GHF9 subgroup E2 genes are relatively rare in bacteria.
Key Words: cellulase • expressed sequence tag • glycosyl hydrolase • horizontal gene transfer
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