Plant Secondary Metabolism

Summary

Biotechnological exploitation of plant cell cultures for production of natural products will depend on our ability to modify expression of complex biosynthetic pathways both quantitatively and qualitatively. De novo, transcriptional activation of genes encoding biosynthetic pathway enzymes represents the first, and often the major, control point for product accumulation, particularly for elicitor-inducible pathways. There is, however, evidence that steady state enzyme levels may also depend on post-transcriptional events such as mRNA and protein turnover. With the complete biosynthetic machinery in place, fine control of pathway flux may be dictated by kinetic criteria for single linear pathways, or by physical channeling of intermediates into parallel pathways, perhaps involving enzyme complexes incorporating specific isoforms of key regulatory enzymes. Examples of the above mechanisms, and their relevance for attempts to alter pathway flux by genetic engineering, are discussed in relation to the phenylpropanoid pathway.