Antifungal biosynthesis by root-associated Streptomyces and Pseudomonas is elicited upon plant colonization

Plants are colonized by a diverse microbiome, with microorganisms residing inside and outside of plant tissues. Plants can harness the protective traits of their microbial inhabitants to ward off insect pests and fungal pathogens. However, current understanding of the role of commensal interactions on activating the desired microbial genomic traits remains limited. Here we show that biosynthesis of the antifungal (L)2-5 dihydro-phenylalanine (DHP) by the endophytic Streptomyces sp. PG2 is strongly induced upon colonization of Arabidopsis thaliana . This protects the plant from infection by the fungal root pathogen Rhizoctonia solani , both in vitro and in vivo . Interaction with sugar beets also enhanced DHP production in Streptomyces sp. PG2. We identified the DHP biosynthetic gene cluster (BGC) and showed that heterologous expression of the BGC in DHP non-producer Streptomyces coelicolor conferred plant-inducible DHP production. The BGC was also found in plant-associated Gram-negative bacteria, and in Pseudomonas syringae FF5 we again observed strongly enhanced DHP production upon plant colonization. Collectively, these data provide proof of concept that plant colonization can enhance the biosynthetic potential of root-associated microbe, thereby enhancing plant resilience. This may increase the competitiveness of the microbes within the rhizosphere.