Cooperation and coexpression: how coexpression networks shift in response to multiple mutualists

A mechanistic understanding of community ecology requires tackling the nonadditive effects of multispecies interactions, a challenge that necessitates integration of ecological and molecular complexity-- namely moving beyond pairwise ecological interaction studies and the ‘gene at a time’ approach to mechanism. Here, we investigate the consequences of multispecies mutualisms for the structure and function of genome-wide coexpression networks for the first time, using the tractable and ecologically-important interaction between legume Medicago truncatula, rhizobia, and mycorrhizal fungi. First, we found that genes whose expression is affected nonadditively by multiple mutualists are more highly connected in gene networks than expected by chance and had 94% greater network centrality than genes showing additive effects, suggesting that nonadditive genes may be key players in the widespread transcriptomic responses to multispecies symbioses. Second, multispecies mutualisms substantially ch...