Limonoids are a group of natural plant products whose intricate chemistry has been intensively studied for over 50 years.
The best-known limonoid, azadirachtin, is known for being bee-friendly but having a robust anti-insect effect; others are well-known for contributing bitterness to citrus fruits, whereas further examples such as nimbolide, are being investigated for potential pharmaceutical anti-cancer uses.
But, despite this wealth of analysis, how plants even start to make these useful chemicals has remained a mystery—till now.
Researchers from the Stanford University and John Innes Centre have revealed new genes that encode this high-value chemistry.
The team used genome mining assets to establish three new enzymes which might make the limonoid precursor melianol and therefore signify the preliminary steps of limonoid biosynthesis.
Due to the advanced chemical structure of limonoids, it’s difficult to synthesize these natural products chemically. In consequence, their use is at the moment restricted to what might be extracted from plant supplies.
Understanding how melianol is made opens the way to metabolic engineering of limonoids through which the newly found genes could be expressed in crops or microbial hosts. It’s a step towards giant-scale manufacturing of limonoid pharmaceuticals and possible development of insect-resistant plants.
Limonoids are made by plants relating to the Mahogany (Meliaceae) and Citrus (Rutaceae) families.
Here the John Innes Centre group characterized enzymes from Melia azedarach, a tropical tree from the Meliaceae family. Partners at Stanford University found and tested similar genes from Citrus sinensis (Sweet Orange), which is in an individual household of crops (Rutaceae). The three genes discovered by the Stanford team also generates melianol, which implies the start of limonoid biosynthesis is received between these two distinct families of plants.