Why are there so many carbohydrate-active enzyme-related genes in plants?

Plants contain far more carbohydrate-active enzyme-encoding genes than any other organism sequenced to date. The extremely large number of glycosidase and glycosyltransferase-related genes in plant genomes can be explained by the complex structure of the plant cell wall, by ancient genome duplication and by recent local duplications, but also by the recent emergence of novel and unrelated protein functions based on widely available pre-existing scaffolds.