Metabolic switching and rewiring play a dynamic role in programmed cell differentiation. Many pathogenic microbes need to survive in nutrient-deficient conditions and use the glyoxylate cycle, an anaplerotic pathway of the tricarboxylic acid cycle, to produce carbohydrates.

The plant pathogenic fungus Magnaporthe oryzae (Pyricularia oryzae) has a unique chitin deacetylase, Cbp1. The spatiotemporal activity of this protein is required for modification of the M. oryzae wall and for cell differentiation into the specialized infection structure (appressorium). Here we show that acetic acid, another product released by the Cbp1-catalyzed conversion of chitin into chitosan, induces appressorium formation. An extremely low concentration (fM) of acetic acid restored cell differentiation in a Δcbp1 mutant possibly through the glyoxylate cycle.