Redirecting Substrate in the Flavonoid Pathway

The flavonoid pathway contains many branch points at which enzymes may compete for substrate, depending on the spatial and temporal occurrences of the enzymes and any metabolite channeling effects. Altering the balance of the competing activities may alter the levels of the different enzyme products and their derivatives. Alternatively, when a potential substrate is accumulating in tissues, a rate-limiting step may be overcome by increasing levels of the required enzyme. 

The overproduction of an enzyme at a rate-limiting step to increase levels of specific flavonoids is well illustrated by the Forsythia ANS example described earlier, and also by the use of CaMV35S CF[I increase flavonol levels in A. thalicma and L. esculentum. In particular, fruit of L. esculentum plants expressing P. hybrida CHI had up to a 78-fold increase in flavonol content, principally rutin, in fruit peel. 

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