Plant specialized metabolites have ecological functions, yet the presence of numerous uncharacterized biosynthetic genes in plant genomes suggests that many molecules remain unknown. We discovered a triterpene biosynthetic network in the roots of the small mustard plant Arabidopsis thaliana. Collectively, we have elucidated and reconstituted three divergent pathways for the biosynthesis of root triterpenes, namely thalianin (seven steps), thalianyl medium-chain fatty acid esters (three steps), and arabidin (five steps). A. thaliana mutants disrupted in the biosynthesis of these compounds have altered root microbiota. In vitro bioassays with purified compounds reveal selective growth modulation activities of pathway metabolites toward root microbiota members and their biochemical transformation and utilization by bacteria, supporting a role for this biosynthetic network in shaping an Arabidopsis-specific root microbial community.

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Jasmonic acid (JA) is a well-known defence hormone, but its biological function and mechanism in rice root development are less understood. Here, we describe a JA-induced putative receptor-like protein (OsRLK, AAL87185) functioning in root development in rice. RNA in situ hybridization revealed that the gene was expressed largely in roots, and a fusion protein showed its localization on the plasma membrane. The primary roots in RNAi transgenic rice plants meandered and curled more easily than wild-type (WT) roots under JA treatment. Thus, this gene was renamed Oryza sativa root meander curling (OsRMC). The transgenic primary roots were shorter, the number of adventitious roots increased and the number of lateral roots decreased as compared to the WT. As well, the second sheath was reduced in length. Growth of both primary roots and second sheaths was sensitive to JA treatment. No significant change of JA level appeared in the roots between the transgenic rice line and WT. Expression of RSOsPR10, involved in the JA signalling pathway, was induced in transgenic rice. Western blotting revealed OsRMC induced by JA. Our results suggest that OsRMC of the DUF26 subfamily involved in JA signal transduction mediates root development and negatively regulates root curling in rice.