Acyl Sugars Protect a Wild Tobacco from Both Native Fungal Pathogens and a Specialist Herbivore.

-Acyl sugars (-AS) are abundant trichome-specific metabolites that function as indirect defenses against herbivores of the wild tobacco ; whether they also function as generalized direct defenses against herbivores and pathogens remains unknown. We characterized natural variation in AS among 26 accessions and examined their influence on two native fungal pathogens, U4 and sp. U10, and the specialist herbivore At least 15 different AS structures belonging to three classes were found in leaves. A 3-fold quantitative variation in total leaf AS was found among the natural accessions. Experiments with natural accessions and crosses between high- and low-AS accessions revealed that total AS levels were associated with resistance against herbivores and pathogens. Removing AS from the leaf surface increased growth rate and plant fungal susceptibility. -AS supplementation in artificial diets and germination medium reduced growth and fungal spore germination, respectively. Finally, silencing the expression of a putative branched-chain α-ketoacid dehydrogenase E1 β-subunit-encoding gene () in the trichomes reduced total leaf AS by 20% to 30% and increased susceptibility to pathogens. We conclude that AS function as direct defenses to protect plants from attack by both native pathogenic fungi and a specialist herbivore and infer that their diversification is likely shaped by the functional interactions among these biotic stresses.