This research identifies how the fungus Aspergillus niger recognizes and responds to different types of sugars found in plant cell walls. Scientists discovered that the fungus uses two control proteins (AraR and XlnR) that are activated by specific sugar molecules: L-arabitol for AraR and D-xylose for XlnR. Importantly, the fungus can distinguish between left and right-handed versions of these sugars, showing remarkable chemical specificity. This understanding is important for biotechnology applications including biofuel and biochemical production.