Functional diversity and metabolic engineering of plant-specialized metabolites.

Plants are talented biochemists that produce a broad diversity of small molecules. These so-called specialized metabolites (SMs) play critical roles in the adaptive evolution of plants to defend against biotic and abiotic stresses, attract pollinators, and modulate soil microbiota for their own benefits. Many plant SMs have been used as nutrition and flavor compounds in our daily food, as well as drugs for treatment of human diseases. Current multi-omics tools have significantly accelerated the process of biosynthetic pathway elucidation in plants through correlation analyses, genetic mapping, and biosynthetic gene cluster predictions. Understanding the biosynthesis of plant SMs has enabled reconstitution of naturally occurring specialized metabolic pathways in microbial hosts, providing a sustainable supply of these high-value molecules. In this review, we illustrate the general functions of several typical plant SMs in natural ecosystems and for human societies. We then provide an overview of current methods elucidating the biosynthetic pathways of plant SMs, and synthetic biology strategies that optimize the efficiency of heterologous biosynthetic pathways in microbial hosts. Moving forward, dissection of the functions and application of plant SMs by using current multidiscipline approaches would be greatly benefit to the scientific community and human societies.