Exploring the metabolic basis of growth/defense trade-offs in complex environments with Nicotiana attenuata plants cosilenced in NaMYC2a/b expression.

In response to challenges from herbivores and competitors, plants use fitness-limiting resources to produce (auto)toxic defenses. Jasmonate signaling, mediated by MYC2 transcription factors (TF), is thought to reconfigure metabolism to minimize these formal costs of defense and optimize fitness in complex environments. To study the context-dependence of this metabolic reconfiguration, we cosilenced NaMYC2a/b by RNAi in Nicotiana attenuata and phenotyped plants in the field and increasingly realistic glasshouse setups with competitors and mobile herbivores. NaMYC2a/b had normal phytohormonal responses, and higher growth and fitness in herbivore-reduced environments, but were devastated in high herbivore-load environments in the field due to diminished accumulations of specialized metabolites. In setups with competitors and mobile herbivores, irMYC2a/b plants had lower fitness than empty vector (EV) in single-genotype setups but increased fitness in mixed-genotype setups. Correlational analyses of metabolic, resistance, and growth traits revealed the expected defense/growth associations for most sectors of primary and specialized metabolism. Notable exceptions were some HGL-DTGs and phenolamides that differed between single-genotype and mixed-genotype setups, consistent with expectations of a blurred functional trichotomy of metabolites. MYC2 TFs mediate the reconfiguration of primary and specialized metabolic sectors to allow plants to optimize their fitness in complex environments.