The transcriptional regulation of specialized terpenoid biosynthesis and its regulation by jasmonic acid

All plants produce terpenoids for their general metabolism but most, if not all, also produce terpenoids in their specialized metabolism. These specialized metabolites play an essential role in the interaction of plants with their environment, in particular with other organisms. They are also of great economic value to us as they are used as medicine, in our food and as perfumes. The regulation of terpenoid biosynthesis has received much attention as it is costly for the plants to produce even though they only contain carbon, hydrogen and oxygen. Some terpenoids are constitutively produced but most of them are induced upon biotic stress with a key role for the phytohormone jasmonate-isoleucine (JA-Ile). It has become clear that the regulation is mostly at the level of transcription with an important role for basic-helix-loop-helix (bHLH) and MYB transcription factors in the JA-Ile inducible pathways. This review summarizes recent breakthroughs with examples of specific mono-, sesqui- and diterpenoids, describing the complex molecular network regulating their biosynthesis in certain model systems with other phytohormones involved as well. It also points out that several other avenues of regulation need more attention to understand the fine tuning of the regulation. This will help optimizing the production of these specialized metabolites in our crops.