Gene Family Expansions Provide Molecular Flexibility Required for Context-Dependent Species Interactions.

As environments worldwide change at unprecedented rates during the Anthropocene, understanding context dependency-how species interactions vary depending on environmental context-is crucial. Combining comparative genomics across 42 angiosperms with transcriptomics, genome-wide association mapping and gene duplication origin analyses, we show for the first time that gene family expansions are important to context-dependent regulation of species interactions. Gene families expanded in mycorrhizal fungi-associating plants display up to 200% more context-dependent gene expression and double the genetic variation associated with mycorrhizal benefits to plant fitness. Moreover, we discover these gene family expansions arise primarily from tandem duplications with > 2-times more tandem duplications genome-wide, indicating gene family expansions continuously supply genetic variation, allowing fine-tuning of context dependency in species interactions throughout plant evolution. Taken together, our results spotlight how widespread gene duplications can provide molecular flexibility required for plant-microbial interactions to match changing environmental conditions.