Periodic Reporting for period 1 - EXTRIDIM (Exploring Triterpene Diversity in Monocots)
Reporting period: 2020-09-01 to 2022-08-31
Triterpenes are one of the most diverse groups of plant natural products, with important roles in plant defense and wide use in medicine, food, and cosmetics. So far, studies on triterpene biosynthesis have largely focused on eudicot plants, while little is known about triterpene biosynthesis in monocots. Here, we set out to expand current knowledge of triterpene chemistry and biochemistry in monocots and to investigate mechanisms of metabolic diversification in this group of plants, and specifically in the cereals group, which together provides more than half of the global human caloric intake. A genome-wide search of pathogen-induced biosynthetic gene clusters (BGCs) in wheat and Brachypodium distachyon ultimately led us to discover two triterpenoids, namely ellarinacin and brachynacin, characterize their biosynthetic pathways and obtain data supporting their putative roles in defense against plant pathogens. We also expanded our investigations beyond the initially planned focus on triterpenes, and further discovered novel metabolic pathways in wheat, which produce defense-related flavonoids and diterpenes. The flavonoid-, diterpene- and triterpene-associated BGCs we identified in wheat were also found to be regulated by a highly overlapping network of transcription factors predicted to interact with multiple genes from the pathogen-responsive BGCs identified. These findings advance our understanding of chemical defenses in wheat and open up new avenues for enhancing disease resistance in this agriculturally important crop. They also exemplify the power of transcriptional networks to discover the biosynthesis of chemical defenses in plants with large, complex genomes.
Our general aim was to expand current knowledge of triterpene metabolism in the Poaceae (grasses) family, which is currently poorly understood. To do this we set to employ a genomics-driven approach, in search of potential triterpene-related biosynthetic gene clusters. This search eventually resulted in identification and characterization of several BGCs in wheat and B. distachyon, identification of novel metabolites produced by these gene clusters and investigation of their possible roles in-planta and bioactivities. Our initial in-silico genome mining approach enabled us to identify 43 candidate triterpene gene clusters in the 12 cereal genomes that were analyzed. As the project progressed, we focused our work on wheat, and expanded our search beyond triterpenes to also identify putative gene clusters for other classes of specialized metabolites.
By combining data from a weighted gene co-expression network analysis (WGCNA), and mining for gene clusters, we identified 6 candidate BGCs, on which we subsequently focused on. For our experimental work, we mainly utilized a transient expression system in Nicotiana benthamiana (agroinfiltration) as means of identifying enzymatic activity for our candidate genes. This system proved to be very useful, eventually allowing us to assign enzymatic activity of >20 enzymes. Analysis of gene expression patterns of the clustered genes showed that they are induced by pathogen infections, suggesting defense-related roles for the metabolites which they collectively produce.
Some of the findings generated in EXTRIDIM were published in the article 'pathogen-induced biosynthetic pathways encode defense-related molecules in bread wheat' (Polturak et al., PNAS, 2022). Additional findings from the project are anticipated to be published in the near future.
By combining data from a weighted gene co-expression network analysis (WGCNA), and mining for gene clusters, we identified 6 candidate BGCs, on which we subsequently focused on. For our experimental work, we mainly utilized a transient expression system in Nicotiana benthamiana (agroinfiltration) as means of identifying enzymatic activity for our candidate genes. This system proved to be very useful, eventually allowing us to assign enzymatic activity of >20 enzymes. Analysis of gene expression patterns of the clustered genes showed that they are induced by pathogen infections, suggesting defense-related roles for the metabolites which they collectively produce.
Some of the findings generated in EXTRIDIM were published in the article 'pathogen-induced biosynthetic pathways encode defense-related molecules in bread wheat' (Polturak et al., PNAS, 2022). Additional findings from the project are anticipated to be published in the near future.
Wheat is one of the most widely grown food crops in the world, however it suffers major yield losses to pests and pathogens. Despite its agricultural importance, surprisingly little is known about the chemicals it produces in response to pathogen challenges.
We used a genomics-driven approach to uncover previously unknown defense-related metabolism in wheat. Our research has led to the identification of several pathogen-induced metabolic pathways that produce a variety of previously unknown defense-related molecules, including triterpenes, diterpenes and flavonoids.
These pathways are encoded by a number of biosynthetic gene clusters that share a common regulatory network and together form part of an orchestrated defense response. Our findings advance current understanding of chemical defenses in wheat and may open new avenues for enhancing disease resistance in this agriculturally important crop in the future.
We used a genomics-driven approach to uncover previously unknown defense-related metabolism in wheat. Our research has led to the identification of several pathogen-induced metabolic pathways that produce a variety of previously unknown defense-related molecules, including triterpenes, diterpenes and flavonoids.
These pathways are encoded by a number of biosynthetic gene clusters that share a common regulatory network and together form part of an orchestrated defense response. Our findings advance current understanding of chemical defenses in wheat and may open new avenues for enhancing disease resistance in this agriculturally important crop in the future.