Location: Corn Insects and Crop Genetics Research
2022 Annual Report
Objectives
Objective 1. Discover diverse fungal disease resistance mechanisms in cereal (barley and maize) crops.
Sub-Objective 1A. Use expression quantitative trait locus (eQTL) analysis in combination with genome-wide promoter-motif enrichment strategies to discover master regulators of immunity.
Sub-Objective 1B: Identify host targets of pathogen effectors by next generation yeast-two-hybrid interaction screens.
Sub-Objective 1C: Identify and characterize the genetic and molecular pathological modes of action for isolate-specific and non-specific Quantitative Disease Resistance (QDR) mechanisms that protect corn plants against northern leaf blight.
Objective 2: Generate novel sets of disease defense alleles for mechanistic dissection and application to crop protection.
Sub-Objective 2A: Functional confirmation via integrated reverse genetic analysis.
Sub-Objective 2B: Evaluate yield and northern leaf blight resistance properties of QDR alleles in hybrid genetic contexts.
Approach
Large-scale sequencing of plant and pathogen genomes has provided unprecedented access to the genes and gene networks that underlie diverse outcomes in host-pathogen interactions. Determination of regulatory focal points critical to these interactions will provide the molecular foundation necessary to dissect important disease resistance pathways. This knowledge can be used to guide modern plant breeding efforts in response to pathogens that present diverse challenges to the host.
Progress Report
Fungal pathogens represent a large and economically significant challenge to crops worldwide. To lessen the impact of fungi on our food sources, a variety of biological, chemical, and mechanical methods are employed, to varying degrees of success. Recent efforts have focused on utilizing molecular genetic methods to facilitate the development of genetically resistant crops, which would reduce the need for, and damage caused by, chemical fungicides. For these methods to be effective and durable, however, there must be a thorough understanding of the molecular interactions between crops and their pathogens.
Plant-pathogen interactions of the cereal grain crops, barley and corn, have been used to identify components of host disease defense and the pathogen signaling molecules that suppress them, with the goal of establishing a fundamental knowledge base to produce productive, disease resistant crops. Obligate biotrophic fungi (e.g., mildews and rusts), which parasitize living host cells, cause some of the most destructive epidemics. The interaction between barley (Hordeum vulgare L.), and the powdery mildew fungus, Blumeria graminis f. sp. hordei, is central to address this challenge. As a model for the large-genome Triticeae (barley, wheat, and rye), this research generates the knowledge base to drive scientific advances that ultimately improve crop productivity, pest and disease resistance, and tolerance to climate change.
Objective 1, Sub-Objective 1A: In research funded in part by the National Institute of Food and Agriculture, in collaboration with Iowa State University scientists, we used a combination of computer- and laboratory-based methods to predict over 66,000 possible protein-protein interactions in barley. The barley predicted interactome was then customized by the integration of defense-specific genomic datasets to model cellular response to powdery mildew infection. These discoveries provide a foundation for further research into the complex molecular components that control disease resistance in crops.
Objective 2, Sub-Objective 2A: In order to prevent economic loss caused by powdery mildew, plant breeders incorporate disease resistance genes into varieties that are grown for food, feed, fuel and fiber. One of these resistance genes provides instructions for assembly of the barley mildew locus a (MLA) immune receptor, an ancestral cereal protein that confers recognition to powdery mildew, stem- and stripe rust, which are ascomycete and basidiomycte fungi with vastly different life cycles. However, in order to function properly, these immune receptors must interact with other helper proteins during the different stages of fungal infection and plant defense. In particular, the SGT1 protein acts to stabilize the MLA immune receptor. Yet, SGT1 has been difficult to investigate in its native state as deletions are lethal. In collaboration with Iowa State University scientists we identified a rare two amino-acid deletion mutant of SGT1, which alters resistance conferred by MLA, but without lethality. Yeast chromosome engineering and advanced protein detection methods demonstrated that the two amino acid domain is critical for SGT1 interactions with the MLA disease resistance protein, which is required for disease defense. Combined with other recent evidence, these results indicate that the two amino acid mutation is a valuable resource to probe the molecular mechanisms of immune receptors by separating disease resistance signaling from other cellular processes.
Accomplishments
1. Genome-wide analysis of protein-protein interactions that control disease resistance in barley. To prevent economic loss due to disease, plant breeders incorporate resistance genes into varieties that are grown for food, feed, fuel and fiber. One of these resistance genes provides instructions for assembly of the barley mildew locus a (MLA) immune receptor, an ancestral cereal protein that confers recognition to powdery mildew, stem- and stripe rust. To function properly, these immune receptors must interact with other helper proteins during the different stages of fungal infection and plant defense. As recently published as the cover article in GENETICS, USDA-ARS scientists in Ames, Iowa, in collaboration with Iowa State University used custom Big Data methods to identify over 66,000 protein-protein interactions and model cellular response to powdery mildew infection. In particular, fifteen new MLA-interacting proteins were identified, predicted to localize to five diverse cellular locations over the course of infection. These results anchor new disease-resistance interactions within the cell during MLA-mediated immune response and will enable future work to understand key components of disease defense. This will promote new investigations from lab to fields, critical to breeders and growers that use disease resistance to produce better crops. This work was funded by the USDA-ARS, the USDA-National Institute of Food and Agriculture, the National Science Foundation, and Fulbright - Minciencias & Schlumberger Faculty for the Future fellowships.
Review Publications
Weldekidan, T., Manching, H., Choquette, N., de Leon, N., Flint-Garcia, S.A., Holland, J.B., Lauter, N.C., Murray, S.C., Xu, W., Goodman, M., Wisser, R.J. 2022. Registration of tropical populations of maize selected in parallel for early flowering time across the United States. Journal of Plant Registrations. 16(1):100-108. https://doi.org/10.1002/plr2.20181.
Wlezien, E.B., Peters, N.T., Wise, R., Boury, N. 2022. Role of crop genetic diversity on pathogen impact: The tale of two pathogens. CourseSource. https://doi.org/10.24918/cs.2022.14.
Velasquez-Zapata, V., Elmore, J., Fuerst, G.S., Wise, R.P. 2022. An interolog-based barley interactome as an integration framework for immune signaling. Genetics. 221(2). Article iyac056. https://doi.org/10.1093/genetics/iyac056.
Chapman, A.V., Elmore, J., McReynolds, M., Walley, J., Wise, R.P. 2021. SGT1-specific domain mutations impair interactions with the barley MLA6 immune receptor in association with loss of NLR protein. Molecular Plant-Microbe Interactions. 35(3):274-289. https://doi.org/10.1094/MPMI-08-21-0217-R.
