Abstract
Growth-defense tradeoffs are a major constraint on plant evolution. While the genetics of resource allocation is well established, the regulatory role of plant-associated microorganisms is still unclear. Here, we demonstrate that plant-associated microorganisms can reposition the plant phenotype along the same growth-defense tradeoff that determines phenotypic effects of plant mutations. We grew plants with microorganisms altering ethylene balance, a key hormone regulating plant investment into growth and stress tolerance. Microbial ethylene reduction had a similar effect to mutations disrupting ethylene signaling: both increased plant growth but at the cost of a strong stress hypersensitivity. We conclude that microbial impact on phenotype can offset the effects of mutations and that apparent plant growth promotion has strong pleiotropic effects. This study confirms that plant life history should be addressed as a joint product of plant genotype and its associated microbiota.