Location: Chemistry Research2013 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.
3. Progress Report:
This work directly relates to sub-objective 1a. 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: Two novel acidic sesquiterpenoid phytoalexins, termed zealexin A4 and zealexin B3, have been discovered in maize. Zealexin A4 exhibits significant antimicrobial activity against a range a fungal pathogens including Southern Leaf Blight (Cochliobolus heterostrophus) and Aspergillus flavus. A transposon insertion mutant in the gene AntherEar2, encoding an ent-copalyl diphosphate synthase, was identified in the maize W22 background. Maize plants homozygous for this mutation completely lack production of all kauralexin diterpenoid phytoalexins following insect and pathogen attack. Propagated seeds are currently being used in greenhouse and field experiments to examine altered resistance phenotypes with naturally occurring fungal and insect pests. Whole transcriptome shotgun sequencing, termed RNA-seq, of seedling scutella tissue revealed candidate a type II kaurene synthase for the kauralexin biosynthetic pathway. Preliminary analysis of this transposon insertion mutant supports the role of this enzyme as a second step in the pathway. Further functional characterization of this inducible maize kaurene synthase is currently underway.