Soil-borne microbes/fungi can establish mutualistic relationships with host plants, providing a large variety of nutritive and protective compounds in exchange for photosynthesized sugars. However, the molecular signals mediating the establishment of these beneficial relationships remain unclear. Our previous genetic mapping and whole-genome resequencing studies identified a gene deletion event of a lectin receptor-like kinase gene PtLecRLK1 in Populus that was associated with poor root colonization by the ectomycorrhizal fungus Laccaria bicolor. By introducing PtLecRLK1 into a perennial grass known to be a non-host of L. bicolor, switchgrass (Panicum virgatum L.), we found that the L. bicolor colonizes the PtLecRLK1 transgenic switchgrass roots which illustrates that introduction of PtLecRLK1 has the potential to convert a non-host to a host of L. bicolor. Further transcriptomic and proteomic analyses on inoculated transgenic switchgrass root samples revealed genes/proteins overrepresented in the mutualistic interaction and underrepresented in the pathogenic defense pathway, consistent with the view that pathogenic defense response is downregulated during mutualistic interaction. Metabolomic profiling revealed that root colonization in the transgenic switchgrass was associated with an increase in N-containing metabolites and a decrease in organic acids, sugars, and phenolics-like hydroxycinnamate conjugates, which are often seen in the early steps of establishing mutualistic interactions in compatible partners. This work illustrates that PtLecRLK1 is able to render a plant susceptible to colonization by the ectomycorrhizal fungus L. bicolor and sheds light on engineering mycorrhizal symbiosis into a non-host to enhance plant productivity and fitness in marginal lands.