Science 364, eaau6389 (2019)

Plants biosynthesize a variety of terpene natural products, many with antimicrobial activities. Seeking to understand an ecological role for these metabolites, Huang and Jiang et al. used heterologous expression, genetic manipulation, and targeted metabolomics to identify a collection of triterpene metabolites in Arabidopsis thaliana. They also characterized and assigned functions to multiple previously unknown biosynthetic genes, enabling the elucidation of the intertwined biosynthetic pathways to thalianin, arabidin, and a group of thalianol-derived fatty acid esters. Disruption of thalianin biosynthesis led to the root microbiota being depleted of Deltaproteobacteria and enriched in Bacteroidetes strains, whereas a cocktail of purified triterpene compounds promoted in vitro growth of Proteobacteria strains isolated from A. thaliana roots and inhibited growth of Actinobacteria strains. Further investigation of the isolated bacteria also revealed that some contained enzymes for additional modification of thalianol-derived compounds. Together, these results indicate how the plant uses secondary metabolites to tune the composition of its root microbiota.