Location: Corn Insects and Crop Genetics Research2018 Annual Report
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.
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.
Fungal pathogens are a major threat to crop production worldwide. This results in severe yield loss to the producer, and increased costs for the consumer. Pathogens secrete effectors to activate and/or suppress plant immune signaling, downstream defense responses, and other cellular processes to enable colonization and nutrient acquisition. To defend themselves, plants have evolved a battery of receptors that activate immune responses via recognition of pathogen-associated molecular patterns (PAMPs), or by recognition of pathogen effectors. Many aspects of plant defense have been studied using a traditional gene-by-gene approach. However, a holistic view of the regulatory programs that render a plant resistant to pathogens is only beginning to emerge in model organisms, and is still in its infancy in large-genome cereals such as barley and corn that are vital to the agricultural economy. This report represents a new 5-year project that started on April 11, 2018. Two host-pathogen systems are being investigated: 1. Barley and barley powdery mildew, and 2. Corn (maize) and northern leaf blight. For barley-powdery mildew interactions, we have initiated work towards the early milestones: 1. Subset host response genes associated with powdery mildew infection stages for initial gene promoter analyses, and 2. Bioinformatic selection of optimal pathogen effectors for use as baits in a genome-wide screen of host interacting proteins using next generation sequencing and yeast-two-hybrid interaction analysis. For maize-northern leaf blight interactions, we have also initiated work to meet milestones for the coming year. To “assess quantitative disease resistance reactions of four northern leaf blight isolates a corn hybrid panel”, we are generating hybrid seed for the panel and have begun producing fungal inoculum for the tests. To “conduct recombination screen at six quantitative disease resistance loci”, we are producing 2,000 DNA samples that correspond with 2,000 seed packages to allow recombinant breeding. To “produce seeds for transgenic iso-hybrid trials”, we are first verifying that our transgenic events are both functional and true-breeding. Lastly, to introgress quantitative disease resistance alleles into inbred lines, we are making crosses from true-breeding sources to these three inbreds. These efforts are all targeted at providing a better understanding of cereal genes and gene networks that regulate disease resistance and susceptibility.