Pathway Gene Paralogues and Transcription Factors Differentially Associate with Contents of Picrosides in Tissues and Populations of a Medicinal Herb, Picrorhiza kurroa

Picrorhiza kurroa is a valuable medicinal herb of Himalayan region, containing two major pharmacological iridoid glycosides: Picroside-I and Picroside-II, in addition to several other secondary metabolites. The metabolic diversity of P. kurroa may stem from the evolutionary processes attributed to pathway genes family expansion via gene duplication or splicing giving rise to paralogues which are further controlled by regulatory components. Occurrence of multiple pathway gene paralogues coupled with which TFs associate with paralogues in different genetic backgrounds (populations) in tissue-specific manner are still unresolved. Here, we unravelled possible correlations between TFs and gene paralogues across a range of P. kurroa accessions which might be contributing to differential contents of Picroside-I and Picroside-II in different tissues/organs. Characterization of shoots, roots, and stolons of eighty-five accessions of P. kurroa revealed significant variations for Picroside-I and Picroside-II contents. Comparative transcriptome analysis of shoot-derived transcriptome (PKSS), and root-derived transcriptome (PKSR) followed by their expression analysis in different P. kurroa accessions revealed TFs; PkWRKY71, PkWRKY12, PkNAC25, and PkMyb46 possibly regulate different gene paralogues. Genes encoding these putative TFs and pathway gene paralogues were further used to generate a robust co-expression network, thereby, uncovering their coordinated behaviour in association with Picroside-I and Picroside-II contents in shoots and roots, respectively. The outcome has provided potential leads, which through further functional validation can provide suitable targets, either for pathway engineering or as gene markers for selection of genetically superior populations of P. kurroa.