Location: Chemistry Research2018 Annual Report
The overall goal of this project is to provide stakeholders with increased knowledge of the innate immune responses of maize to insect and fungal attack and determine how these defense mechanisms are affected by abiotic stress factors. Objective 1. Molecularly characterize the production and function of chemical defense responses to biotic and abiotic stress of maize to evaluate and elucidate the cumulative effect of multiple stressors. Sub-objective 1A. Molecularly characterize defense metabolites (i.e., fatty acids) and their mediated plant responses in fungal infected tissues, and determine the impact of abiotic stress on these responses. Sub-objective 1B. Identify maize genes involved in the production of chemical defenses against insect pests, use mutants in these genes to elucidate the production and function of chemical defenses in insect resistance, and assess the effect of abiotic stress on these defenses. Objective 2. Identify and functionally characterize genetic components that mediate the defense response of maize to biotic stress, and determine the impact of abiotic stress on these mechanisms to mitigate yield loss.
The production of select chemical defenses in maize in response to specific biotic stressors will be analyzed by profiling novel free fatty acids, hormones, inducible volatiles, and flavones in maize in response to fungal or insect attack. Candidate genes responsible for the biosynthesis and regulation of these metabolites will be identified using co-expression analysis and forward genetic approaches. Once the genes have been selected they will be prioritized for further characterization and mutant resources such as the UniformMu maize population mined for mutations in those genes and the presence of mutant alleles confirmed by gene-by –gene PCR genotyping. Mutants will also be generated in genes of interest using CRISPR/Cas9 technology. Loss-of-function mutants, coupled with metabolic profiling and bioassays will then be used to assess the function of select high priority candidate genes and their products in biotic stress resistance. Furthermore, defense responses will be characterized under abiotic stress conditions (heat, drought, elevated carbon dioxide) to determine the integrity of defense pathways under situations of combinatorial stress.
Good progress has been made on the research project 6036-11210-001-00D by Gainesville ARS researchers. Two genome wide association study (GWAS) experiments were carried out on the Goodman 282 diversity panel. The first experiment tested cell death sensitivity to the phytoxic compound 10-oxo-phytoenoic acid (10-OPEA). Treated leaves were collected and imaged for digital lesion area measurements and the data was summarized and formatted for mapping analysis. The second experiment investigated defense metabolite concentrations in Cochliobolus heterostrophus (Southern leaf blight)-infected stems. The infected stems from the 282 panel were collected, processed, and run on a CI-GC/MS. This data was also analyzed, summarized, and formatted for genomic mapping. Co-expression analysis was used to identify 17 new candidate genes for defense compound production. Ten new UniformMu alleles for potential mutants in several of these genes were identified and are currently planted in the field for genotyping. Two CRISPR/CAS9 constructs were designed and made, each targeting 2 candidate genes and sent to the transformation core facility to obtain mutant alleles. More than 50 mutant lines are currently being introgressed into W22, B104 or B73 inbred lines. Maize lines altered in hormone production were also used in select bioassays. These include: assays to the production of herbivore induced volatiles and fall armyworm feeding preference and growth in abscisic acid (ABA)-deficient lines, fungal susceptibility assays in jasmonic acid-deficient and jasmonic acid-overaccumulating lines, and fungal susceptibility assays in ABA-deficient kernels.
Beck, J.J., Alborn, H.T., Block, A.K., Christensen, S.A., Hunter III, C.T., Rering, C.C., Seidl-Adams, I., Stuhl, C.J., Torto, B., Tumlinson, J.H. 2018. Interactions among plants, insects, and microbes: elucidation of inter-organismal chemical communications in agricultural ecology. Journal of Agricultural and Food Chemistry. 66(26):6663-6674. doi:10.1021/acs.jafc.8b01763.