Metabolic engineering in plants for human health and nutrition.

In many cases, multiple pathway enzymes need to be upregulated to produce a significant yield of a desired product. Technical advances in simultaneously manipulating multiple steps in plant metabolic pathways include the use of transcription factors, such as MYB12. By upregulating the genes of an entire pathway, these factors can greatly simplify multienzyme engineering. Furthermore, synthetic zinc-finger protein transcription factors can now be designed to target specific pathway enzymes, such as tocopherol methyltransferases. When multiple steps in a pathway are upregulated, previously unsuspected facets of the pathway might be revealed, such as the newly uncovered bifunctional substrate preference of the key regulatory enzyme in tocopherol (vitamin E) biosynthesis, homogentisate phytyltransferase. The engineering of desired traits, such as long-chain omega-3 polyunsaturated fatty acids, can require entirely new pathways to be introduced into a plant. Recent advances in genomics and gene expression technology have made this type of complex metabolic engineering highly feasible.