2012 Annual Report
1a.Objectives (from AD-416):
1. Identify defense-induced small molecules in Arabidopsis, maize, rice, and soybean.
2. Confirm the identity of previously unknown metabolites through de novo synthesis.
3. Study biosynthetic pathways and biological functions for a subset of novel plant metabolites.
1b.Approach (from AD-416):
Elucidate novel bioactive chemicals in maize, rice, soybean and Arabidopsis that function in defense against insects and pathogens. Plants will be challenged with a defined set of elicitors, insects and pathogens. Induced chemical changes will be explored using a series of GC/MS- and LC/MS-based metabolic profiling approaches. Strongly induced unknown analytes will be chromatographically purified and indentified via NMR and synthesis where applicable. Biological activity will be established using previously developed insect and microbial bioassays which monitor for altered growth and fitness. Using available mutants and molecular tools biosynthetic pathways required for these inducible metabolites critically evaluated which, in turn, will identify genetic resources to demonstrate function in planta.
This project is related to inhouse project sub-objective 1.A: Isolation and identification of elicitors or biotic agents of induced plant volatile emission and other inducible plant defenses.
Metabolomics: Identification of inducible bioactive plant metabolites: Novel acidic sesquiterpenoid phytoalexins, termed zealexins, were discovered in Southern Leaf Blight (Cochliobolus heterostrophus) resistant maize lines that were inoculated with this fungus. Additional zealexins were found to strongly accumulate in insect and fungal damaged kernels during development on maturing maize ears. Unknown members of this phytoalexin class were highly enriched in maize lines resistant to aflatoxin accumulation compared to known susceptible lines. Work on structure elucidation and antimicrobial assays began July 30th by grant-funded Research Associate. A time course of maize seedling scutella tissue, harboring high levels of kauralexins and zealexins, was subjected to whole transcriptome shotgun sequencing, termed RNA-seq. This defense enriched transcriptome is currently being screened for cytochrome P450s and other candidate phytoalexin biosynthetic genes which will be biochemically tested for enzyme activity following purification from bacterial and yeast heterologous expression systems.