Multiple ectomycorrhizal fungi (EMF) compete to colonise the roots of a host plant but it is not known whether their success is under plant or fungal control, or a combination of both. Using RNAseq, we assessed whether plants control EMF colonisation by preferentially allocating more carbon (C) to more beneficial partners in terms of nitrogen (N) supply or if other factors drive competitive success. We characterised coordination of nutrient exchange between the plant host Eucalyptus grandis and three Pisolithus isolates when growing alone and when competing either indirectly (with a physical barrier) or directly. Differences in nutrient exchange among isolates were related to differences in expression of key fungal and plant N and C transporter genes. When given a choice of partners, the plant was able to limit colonisation by the least cooperative isolate. This was not explained by a reduction in allocated C. Instead, our results suggest that partner choice in EMF could operate through the up-regulation of defence-related genes against those fungi providing fewer nutrients. \nThis dataset contains approximately 100 subsample folders of RNAseq fastq data. Each sample data comes complete with a matching CSV file of metadata. In total, the dataset volume equates to 150GB.