Peppermint (Mentha x Piperita) and Spearmint (Mentha spicata) belong to the same Mentha genus. They share much of the same molecular machinery. A crucial part of a cell’s molecular mechanism is the microRNAs that regulate the expression of genes. The microRNAs can turn on and off a gene. Genes are segments of DNA that contain the code to create proteins. It is proteins that make useful by-products in the cell, from vitamins and sugars to essential oils in individual plants.
Scientists in India discovered that Peppermint and Spearmint cells share the same three microRNAs—miR156, miR414, and miR5021—responsible for regulating the genes that biosynthesize essential oils. MicroRNAs control dozens of genes. These genes are responsible for creating proteins that ultimately produce essential oils.
Interestingly, even with similar molecular machinery, Spearmint and Peppermint have a different collection of essential oil chemical components. The complexity of chemistry in each essential oil comes from the complications in the molecular machinery of the plants producing essential oils.