Research

Many of the ca. 400,000 species of plants found on earth produce biologically active molecules of extraordinary chemical complexity. Elucidation of the metabolic pathways that generate these molecules has historically been challenging, but over the last 15 years we have developed tools and approaches to streamline plant pathway elucidation and engineering. Our research group has led efforts to elucidate complex plant natural product pathways, and use this knowledge to understand the mechanism, evolution and function of these pathways.

Discovery of new plant biosynthetic genes

We have elucidated many natural product pathways, with a particular focus on the monoterpene indole alkaloids and iridoid natural products. To the left is the biosynthetic pathway of the ipecac alkaloids, a natural product class related to monoterpene indole alkaloids.

Other pathways we have solved include vinblastine, ibogaine, strychnine, kratom alkaloids and nepetalactone, the active ingredient in catnip.

To use our self organizing map developed by Marc Jones in Payne et al. (2017) Nature Plants:

https://github.com/marc-jones/catharanthus-roseus-som.

We use state-of-the-art sequencing and bioinformatics techniques, often in collaboration with the Buell group at the University of Georgia.

We have recently collaborated with the Buell Lab to apply single cell RNA-seq technologies to elucidation of plant pathways. We have recently developed a complementary method for single cell mass spectrometry to use in combination with single cell RNAseq data.

The advances that have been made in omics technologies has revolutionized what we are able to do in plant metabolism.

Mechanism and evolution of biosynthetic pathways

Our group has a strong interest in enzyme mechanism. We use a variety of biochemical and biophysical techniques to understand how enzymes work and how these enzymes can be used in metabolic engineering and as biocatalysts. We are also interested in the evolution of enzymes, and we have used approaches such as ancestral sequence reconstruction to try to understand how unusual enzyme activity may have evolved. The figure on the right illustrates how an enzyme that catalyzes a cycloaddition reaction evolved from an esterase.

We also explore ways in which enzyme mutagenesis leads to divergent evolution, namely the production of highly diverse chemical structures from a single starting substrate.

Sometimes nature evolves different chemical solutions to synthesize the same molecule. In fact, sometimes plants and insects make the same natural product! For example, we are comparing and contrasting the biosynthetic pathway of the natural product nepetalactone in the plant catnip (where nepetalactone is the active ingredient of catnip that makes cats go wild) and aphids. We are looking at the biosynthetic pathways of other terpenes in a variety of insects to understand how natural product biosynthesis evolved differently in plants and animals.

Reconstitution of plant pathways

We are exploring ways to reconstitute individual branches of plant pathways in tractable host organisms, such as Nicotiana benthamiana. We use this approach to better understand the individual steps of the pathway, as well as to try to generate proof of concept reconstitution systems for the production of high value molecules. We also use transient expression of Nicotiana benthamiana capable to produce “new-to-nature” products. This reprogramming of biosynthetic pathways to produce unnatural products may lead to the development of molecules with new biological activities.