Regulation of phytoalexin biosynthesis for agriculture and human health

Phytoalexins are diverse secondary metabolites of plants that are biosynthesized transiently and in relatively low amounts in response to pathogens and certain abiotic stresses. They commonly have potent antimicrobial and medicinal activities. As such, scientists have attempted to increase their accessibility by inventing diverse in vitro and in vivo approaches. Among these approaches, bioengineering plant transcription factors that directly regulate phytoalexin biosynthesis genes may be the most promising. Recent research has identified conserved transcription factors that directly regulate distinct phytoalexin biosynthesis pathways in different plant species. The intriguing results provide new insight into how conserved defense signaling pathways in plants result in lineage-specific biochemical defenses. These recent findings also suggest that a common transcription factor network could be engineered to enhance the biosynthesis of different phytoalexins in plants. However, the picture is far from complete since one or more transcription factors required to fully activate phytoalexin biosynthesis remain unidentified, and the exact mechanism of how the conserved factors regulate diverse phytoalexin pathways remains to be clarified. Here we review the agricultural and medicinal importance of phytoalexins, recent approaches to increase their accessibility, and the mechanisms that plants employ to activate and limit their biosynthesis. This review contributes to providing a systems level understanding of the regulation of phytoalexin biosynthesis so that effective bioengineering strategies can be developed to enhance phytoalexin biosynthesis for medicine and agriculture.