Metabolic arms race between a plant and a fungal pathogen

In this work, we uncover a metabolite interaction between barley and the fungal pathogen Bipolaris sorokiniana ( Bs ), involving hordedanes, a previously undescribed set of labdane-related diterpenoids with antimicrobial properties. Bs infection of barley roots elicits hordedane synthesis from a 600-kb gene cluster. Heterologous reconstruction of the synthesis pathway in yeast produced several hordedanes, including one of the most advanced products 19-b-hydroxy-hordetrienoic acid (19-OH-HTA). Barley mutants in the diterpene synthase genes of the cluster are unable to produce hordedanes but, unexpectedly, show reduced Bs colonization. Accordingly, 19-OH-HTA enhances both germination and growth of Bs , while it inhibits other fungi, and Bs chemically modifies 19-OH-HTA. Thus, plant and pathogen molecular interactions extend beyond protein-protein recognition and the simple detoxification of plant antimicrobial metabolites.