Serendipita is a genus of plant growth-promoting endophytic fungi. In contrast to arbuscular mycorrhizal fungi, Serendipita enhances plant growth mainly by modulating host resource allocation and metabolism rather than through nutrient acquisition. How this occurs is poorly understood, in part due to the difficulty of picking up growth-promoting ‘signals’ amidst the ‘noise’ of the colonization process: colonization induces plant immune responses and transcriptome, proteome and metabolome reprograming through e.g. microbe- and damage-associated patterns, effector proteins and cell death. This ‘background noise’ complicates genetic screens, omics methods and other high-throughput methods. Previous work in our group resulted in a unique collection of 51 Serendipita isolates, divided into seven taxonomically ambiguous genetic groups. Interestingly, plant perception of volatiles released by these isolates phenocopies many effects of direct colonization, including growth promotion, petiole enlargement, anthocyanin accumulation and lateral root elongation. These volatiles may thus provide an exciting tool to split growth promotion by fungal endophytes from the colonization background. In this project, we will use genetic screening, transcriptomics and bioassays to study growth promotion by Serendipita volatiles, use phased genome sequencing to clarify Serendipita taxonomy and genome structure and use metabolomics and genome mining to characterize Serendipita’s volatile repertoire.