Cell‐type‐aware regulatory landscapes governing monoterpene indole alkaloid biosynthesis in the medicinal plant <i>Catharanthus roseus</i>

In plants, the biosynthetic pathways of some specialized metabolites are partitioned into specialized or rare cell types, as exemplified by the monoterpenoid indole alkaloid (MIA) pathway of Catharanthus roseus (Madagascar Periwinkle), the source of the anticancer compounds vinblastine and vincristine. In the leaf, the C. roseus MIA biosynthetic pathway is partitioned into three cell types with the final known steps of the pathway expressed in the rare cell type termed idioblast. How cell-type specificity of MIA biosynthesis is achieved is poorly understood. We generated single-cell multi-omics data from C. roseus leaves. Integrating gene expression and chromatin accessibility profiles across single cells, as well as transcription factor (TF)-binding site profiles, we constructed a cell-type-aware gene regulatory network for MIA biosynthesis. We showcased cell-type-specific TFs as well as cell-type-specific cis-regulatory elements. Using motif enrichment analysis, co-expression across cell types, and functional validation approaches, we discovered a novel idioblast-specific TF (Idioblast MYB1, CrIDM1) that activates expression of late-stage MIA biosynthetic genes in the idioblast. These analyses not only led to the discovery of the first documented cell-type-specific TF that regulates the expression of two idioblast-specific biosynthetic genes within an idioblast metabolic regulon but also provides insights into cell-type-specific metabolic regulation.