Plant root exudates contain a range of low molecular weight metabolites, which are believed to trigger the structural and physiological changes associated with the progression and establishment of the mycorrhizal symbiosis. Glomus intraradices spores were incubated with acetosyringone (AS), and an overall increase in the hyphal respiration was observed, indicating a physiological response triggered by this plant regulator. A G. intraradices cDNA library was then screened with a total cDNA probe obtained from the AS-treated spores and mycelium. The cDNAs from different functional categories were identified as induced in G. intraradices when exposed to AS, such as protein synthesis, membrane transport, signal transduction, general metabolism, without assigned function, and no identity. Interestingly, a cDNA coding for a fragment of a histidine kinase was also induced by AS, suggesting a two-component mediated response. We also demonstrated the differential accumulation of a cruciform DNA-binding protein mRNA, termed as GiBP1. Time-course experiments demonstrated its rapid accumulation within 2h of induction with AS. These results indicate the presence of a set of fungal genes that are induced by the presence of the inducer. These findings are discussed in terms of the possible molecular events that follow the exchange of signals between the mycorrhizal symbionts.