Intermediate results for: Large differences in carbohydrate degradation and transport potential among lichen fungal symbionts

Lichen symbioses are thought to be stabilized by the transfer of fixed
carbon from a photosynthesizing symbiont to a fungus. In other fungal
symbioses, carbohydrate subsidies correlate with reductions in plant cell
wall-degrading enzymes, but whether this is true of lichen fungal
symbionts (LFSs) is unknown. We predicted genes encoding
carbohydrate-active enzymes (CAZymes) and sugar transporters in 46 genomes
from the Lecanoromycetes, the largest extant clade of LFSs. All LFSs
possess a robust CAZyme arsenal including enzymes acting on cellulose and
hemicellulose, confirmed by experimental assays. However, the number of
genes and predicted functions of CAZymes vary widely, with some fungal
symbionts possessing arsenals on par with well-known saprotrophic fungi.
These results suggest that stable fungal association with a phototroph
does not in itself result in fungal CAZyme loss, and lends support to
long-standing hypotheses that some lichens may augment fixed CO2 with
carbon from external sources.