Glucosinolate Regulation in a Complex Relationship – MYC and MYB – No One Can Act Without Each Other

The well-studied pathway of glucosinolate (GSL) biosynthesis in Arabidopsis thaliana serves as a model system for secondary metabolites in plants. Most biosynthetic genes are known and were used in systematic co-expression approaches to identify their transcriptional regulators. Two groups of homologous MYB and bHLH transcription factors (TFs) interact with each other and fulfil the main role of direct regulation. The MYB factors are crucial for the specificity of the pathway and control genes in the core-structure pathway of indolic and aliphatic GSL, respectively, as well as the genes in the primary metabolism for the necessary substrates. The MYC-bHLH TFs are crucial for all types of GSL and act together with both types of MYB factors; furthermore they integrate phytohormone signals specifically from the jasmonate signal transduction to adjust the production of this important defence compound class. The regulation of the modification reactions of GSL is under control of a diverse set of other TFs, which have the potential to fine-tune also the core-structure pathway of the glucosinolate biosynthesis. However, most of these regulators still need to be identified and characterized. Although many aspects and components involved in this transcriptional regulation are known, still not all known glucosinolate profiles can be explained by the activity of these modulators and point to the important role of transport and metabolism in determining accumulation pattern of GSL.