Heterogeneity of iridoid biosynthesis in catmints: Molecular background in a phylogenetic context

Numerous members of the Nepeta genus (family Lamiaceae, subfamily Nepetoideae) are medicinal herbs and sources of important bioactive compounds. Most Nepeta species produce iridoids, which are monoterpenoids that deter herbivores and pathogens and are potential biopesticides. In Nepeta, some species produce iridoid aglycones and glycosylated iridoids (referred to as chemotype A), some produce only glycosylated iridoids (chemotype B), and some produce neither iridoid aglycones nor glycosylated iridoids (chemotype C). Here, we show that the observed diversity in iridoids is, at least partially, attributed to evolutionary gains and losses of key biosynthetic genes. Based on reconstructed phylogenetic relationships, we propose a scenario in which partial or complete loss of the ability to synthesize iridoids with specific stereochemistries in the taxa with chemotypes B and C resulted from independent evolutionary events. These observations improve our understanding of metabolic diversity in the Nepeta genus and may inform efforts to produce specific iridoids in plants.