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

O -Acyl sugars ( O -AS) are abundant trichome-specific metabolites that function as indirect defenses against herbivores of the wild tobacco Nicotiana attenuata ; whether they also function as generalized direct defenses against herbivores and pathogens remains unknown. We characterized natural variation in O- AS among 26 accessions and examined their influence on two native fungal pathogens, Fusarium brachygibbosum U4 and Alternaria sp. U10, and the specialist herbivore Manduca sexta At least 15 different O- AS structures belonging to three classes were found in N. attenuata leaves. A 3-fold quantitative variation in total leaf O- AS was found among the natural accessions. Experiments with natural accessions and crosses between high- and low- O- AS accessions revealed that total O- AS levels were associated with resistance against herbivores and pathogens. Removing O- AS from the leaf surface increased M. sexta growth rate and plant fungal susceptibility. O -AS supplementation in artificial diets and germination medium reduced M. sexta growth and fungal spore germination, respectively. Finally, silencing the expression of a putative branched-chain α-ketoacid dehydrogenase E1 β-subunit-encoding gene ( NaBCKDE1B ) in the trichomes reduced total leaf O- AS by 20% to 30% and increased susceptibility to Fusarium pathogens. We conclude that O- 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.
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