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Modular biochemical networks of maize anti-pathogen defense defined by integrating synthetic biochemistry, genetics and physiological function


Crop biochemical defense mechanisms effective against most pests and diseases are essential to agricultural productivity. The natural genetic diversity among individual cultivars provides unique, but underutilized, layers of stress resilience. Maize (Zea mays) is the agronomically most important U.S. crop and among the most genetically diverse. Conceptually parallel to the sticky sap promoting wound healing in pine trees, maize is protected by inducible chemicals, termed diterpenoids, that act as antibiotics to suppress pest attack and disease. Empirically, maize plants lacking diterpenoid defenses display dramatic increases in fungal disease damage. The current project unveils mechanisms of crop stress resilience by defining the formation and diverse bioactivities underlying maize diterpenoid defenses. Variable chemical diversity between established inbred lines will be leveraged to identify diterpenoid-biosynthetic genes and enzyme functions using state-of-the-art genetic mapping and biochemical technologies. Integrating a systematic array of computational, wet-lab and field-based approaches will discover the biosynthetic machinery, chemical structures, and ecological importance of maize diterpenoids. These deliverables will enable new strategies for enhancing crop protection in the face of pressing needs for improving agricultural productivity. The activation of diterpenoid synthesis by readily available food-grade fungi will be developed as an educational tool in high schools to foster intellectual curiosity about plant immune responses, their agricultural use, and the importance of biochemicals to humans. The project will positively impact society by discovering and harnessing biochemical crop defenses and teaching modern STEM concepts and technologies through implementing high school Lesson Study Modules using our integrated approach.<br/><br/>Complex combinations of biotic and abiotic stressors can overcome crop defenses and promote yield losses. As the dominant global grain crop, maize (Zea mays) contains unique and largely unresolved specialized diterpenoid metabolites that contribute to plant resilience by conferring quantitative protection against pathogens. A foundational understanding and agricultural application of molecular mechanisms underlying maize biochemical networks will be essential to further optimize crop resilience. This collaborative project will leverage complementary genetic, biochemical and ecological approaches to gain a precise mechanistic knowledge of specialized metabolites governing maize disease resistance. Integrating functional genomics, metabolomics, forward genetics, DNA synthesis, and combinatorial in vitro and in vivo protein biochemical approaches will enable rapid pathway discovery to elucidate maize-specific diterpenoid-metabolic networks. Parallel generation and analysis of maize mutants in defined pathway nodes will unravel the interrelations between fungal-elicited diterpenoid biosynthesis and pathogen resistance in planta. In tandem, in vitro anti-fungal bioassays of purified diterpenoids with a range of maize pathogens will illuminate the structure-function relationships underlying diterpenoid bioactivity. The cross-disciplinary nature of this project provides an excellent framework for training postdoctoral, graduate and undergraduate students, and will be leveraged to connect the project team with local high school teachers for developing Lesson Study Modules as a platform to engage high school students in cross-cutting principles underlying plant-pathogen interactions. To promote research and education at the confluence of maize-microbe interactions and agricultural innovation, knowledge, resources such as enzyme/metabolite catalogs, mutant lines, and training modules arising from this work will be broadly shared with the scientific community.<br/><br/>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.

Philipp Zerbe; Eric Schmelz
University of California - San Diego
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