The conspicuous leaf-cutter ants in the genus Atta build huge nests displacing several cubic meters of soil, whereas lower attine genera such as Cyphomyrmex have small nests with a fungus garden the size of a table-tennis ball. Only the leaf-cutter ants are specialized on using fresh leaves as substrate for their fungus gardens, whereas the more basal attine genera use substrates such as flowers, plant debris, small twigs, insect feces and insect carcasses. This diverse array of fungal substrates across the attine lineage implies that the symbiotic fungus needs different enzymes to break down the plant material that the ants provide or different efficiencies of enzyme function. Here we present the fist partial amino acid sequences from a fungal xylanase gene to test the hypothesis that fungal enzymes that degrade plant cell walls have functionally co-evolved with the ants.