CAREER: Engineering plant anthranilate ester synthesis and perception for herbivore defense

Half of all modern medicines are directly derived from or inspired by molecules found in nature, with many of these bioactive natural products produced by plants as defense mechanisms. These mechanisms can be either physical in nature, such as thorns, or chemical, such as anthranilates, with the type of mechanism varying based on the plant. Citrus, grapes, maize, alfalfa, and strawberries produce anthranilates, a group of under-investigated, secondary metabolites that have been demonstrated to deter herbivores and decrease microbial infections in plants.

The goal of this research is to understand how plants produce, and recognize and interact with anthranilates in plants, insects, and mammals. Findings from this research may benefit society by advancing our understanding of plant defense against herbivores and pathogens, which has implications in reducing crop losses by predation and infection, respectively.

This project further supports the U.S. bioeconomy by providing high-quality research experiences to undergraduates and post-baccalaureate researchers. This work integrates into an investigative undergraduate Pharmacology lab course that introduces students to authentic research on bioactive plant metabolites. The project also fosters public engagement through an annual collaboration with fifth-grade classes in Berkshire County, Massachusetts and Bennington County, Vermont called “Making Sense of Plant Scents,” which is a multi-week, hands-on field experiment on the bird-deterrent effects of anthranilates.

Plant chemical defenses are typically secondary or specialized metabolites that are synthesized from primary metabolites, such as amino acids. While all plants synthesize anthranilate as an intermediate in tryptophan biosynthesis, several plants have co-opted anthranilate for defense metabolism. The O-methyl ester of anthranilate is an anti-herbivory volatile responsible for grape aroma that is emitted by grapes, citrus, and maize.

Citrus also synthesizes N-methyl anthranilate esters that have analgesic activity in mammals. This project explores anthranilates across multiple levels: from the molecular level, to between plants, to plant-herbivore interactions. The goals of this project are to identify the molecular determinants of anthranilate ester biosynthesis, engineer plant perception of volatile anthranilates emitted from neighboring plants, and provide a systems-level understanding of the targets of anthranilates in plants and animals.

Aim 1 connects protein structure to function to identify the enzymes responsible for synthesizing anthranilate esters with a focus on bioactive N-methyl anthranilates in citrus. Aim 2 examines the substrate specificity of plant methylesterases, which informs our ability to predict which plants can sense volatile anthranilates and may enable volatile perception engineering.

Aim 3 sheds light on the biological functions of anthranilates in both plants and animals using chemoproteomics to identify the protein targets of anthranilates. Anthranilate esters are an under-investigated area of plant metabolism that is ripe for molecular investigation, and this research expands our fundamental knowledge of the roles of anthranilates in plant defense metabolism in agriculturally relevant plants.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.