To deal with relentless environmental pressures, plants produce an arsenal of structurally diverse defensive chemicals. These sometimes-complex compounds are derived from much simpler building blocks from core metabolic pathways. Unlike well-documented diversification of plant specialized metabolic enzymes, core metabolic pathways are highly conserved and evolutionarily constrained because they serve essential metabolic functions, which makes manipulation of these pathways difficult.

The expansion and alteration of core metabolism has given rise to the evolution of structurally diverse plant specialized metabolites. However, the underlying mechanisms potentiating metabolic diversity and the connections linking core to specialized metabolism are not well known. These knowledge gaps create bottlenecks in synthetic biology platforms for production of high-value plant metabolites and increasing plant resilience.

The goal of the lab is to identify core metabolic innovations that have potentiated chemical diversity in plants and harness these innovations for increased crop resilience and enhanced production of medicinal plant compounds through synthetic biology platforms.

Specific Research Projects

Effects of allelopathic compounds on plant microbiome recruitment

Allelopathic compounds are synthesized and excreted by plants to inhibit growth of surrounding plants and also have affects on other organisms. Azetidine-2-carboxylic acid (Aze) is an allelopathic compound produced in some legume and grass species. It acts as a proline analog and is misincorporated during protein synthesis to inhibit growth of surrounding organisms.

The goals of this project are to define the biosynthetic pathway and how it has evolved in diverse plants. Pathway elucidation will enable discovery of the tools to develop models to investigate how production of Aze effects recruitment of the root microbiome. This will be performed using two approaches, first engineer Arabidopsis to produce Aze, and use CRISPR/Cas9 to knockout Aze biosynthesis in a model legume to investigate effects on root microbiome recruitment. Additionally, we want to understand how species that produce Aze remain resistant and if those mechanisms can be translated into other species to develop new tools for enhanced crop production and resilience.

Acylsugars: a model system to investigate how metabolic innovations drive chemical diversity

Acylsugars are a class of specialized metabolites produced by many species within the Solanaceae family, which contains tomato, potato, eggplant, and other horticultural and medicinal plant species. Acylsugars consist of a sugar core, with esterified acyl chains. These defensive compounds are synthesized in the trichomes on leaf and stem surfaces. The acyl chains are derived from branched chain amino acids, and can undergo elongation to increase the structural variations of acyl chain types. Even though derived from simple building blocks from core metabolism, the potential structural diversity of acylsugars is almost limitless. The acyl chains are sequentially attached to sugar cores by acylsugar acyltransferase (ASAT) enzymes that are highly expressed in the trichomes. The substrate promiscuity of ASATs and upstream metabolic innovations provide a diverse pool of substrates in the trichomes that enable the structural diversity of acylsugars observed across the family.

Evolution and biosynthesis of acylsugar diversity within the Nicotiana genus

Here, we wanted to capture the acylsugar structural diversity across the Nicotiana genus, understand acylsugar biosynthesis using comparative transcriptomics and reconstruct acylsugar biosynthesis in vitro.

Fruit-localized acylsugar secretion and accumulation in tomatillo

Tomatillos are a husked-fruit, closely related to tomato, indigenous to Mexico and the surrounding region and widely used in Mexican cooking. Beneath the husk, the fruit has a sticky surface. Metabolite analysis of the fruit surface and other tissues revealed that acylsugars were highly abundant on fruit surfaces ­­- where trichomes are absent – and only detectable at trace amounts in other tissues, such as leaf and stem surfaces. These data suggest that acylsugars are produced and secreted by the fruit, yet the mechanism remains unknown. In this project we wanted to understand how acylsugars are biosynthesized on the fruit surface.

Checkout an outreach blog post about defensive role of acylsugars in tomatillo.

Co-option of core metabolism leads to increased acylsugar structural diversity

Acyl chains attached to acylsugars are derived from branched chain amino acids. But, acyl chains longer than 4 and 5 carbons in length, upwards of 14 carbons, are found on acylsugars. Interestingly, long chain-containing acylsugars are restricted to certain Solanaceae lineages, suggesting the capacity to elongate acyl chains prior to esterification to the sugar core. Previous feeding studies implicate that species with long chains use a 2-carbon elongation mechanism analogous to fatty acid biosynthesis. The goals of this project are to determine the molecular components involved in acyl chain elongation, disrupt the elongation pathway in tomato using CRISPR/Cas9, trace the evolutionary origins of this molecular co-option, and determine at the molecular level how fatty acid biosynthetic machinery has been modified to accommodate acylsugar biosynthesis in the trichomes.