A simplified glucosinolate biosynthetic pathway illustrating the power and limitations of integrated transcriptomics and metabolomics for identifying specialized metabolic pathways.
The simplified pathway uses tryptophan as a precursor and generates two stable glucosinolate products using several genes and enzymes. Enzymes A and B are directly involved in the production of the first stable product. Enzyme C must be activated by Enzyme D (a kinase) before it can also contribute to the pathway. As a result, Genes A, B, and C are detected in the co-expression network, but Gene C* is not detected because the enzyme isn't generated directly from a transcript. Gene D encoding the kinase may also not be reliably detected in the co-expression network. Enzyme E is directly involved in a final functional modification of stable product 1 to form stable product 2, so it also may not reliably co-express at the same time as the other biosynthetic genes. Metabolic profiles reveal both stable glucosinolate products in addition to the precursor molecule.