A redundant transcription factor network steers spatiotemporal Arabidopsis triterpene synthesis

Plant specialized metabolites modulate developmental and ecological functions and comprise many therapeutic and other high-value compounds. However, the mechanisms determining their cell-specific expression remain unknown. Here we describe the transcriptional regulatory network that underlies cell-specific biosynthesis of triterpenes in Arabidopsis thaliana root tips. Expression of thalianol and marneral biosynthesis pathway genes depends on the phytohormone jasmonate and is limited to outer tissues. We show that this is promoted by the activity of redundant bHLH-type transcription factors from two distinct clades and coactivated by homeodomain factors. Conversely, the DOF-type transcription factor DAG1 and other regulators prevent expression of the triterpene pathway genes in inner tissues. We thus show how precise expression of triterpene biosynthesis genes is determined by a robust network of transactivators, coactivators and counteracting repressors.