Location: Chemistry Research Unit
Title: Kauralexins: newly discovered ent-kaurane-related diterpenoid phytoalexins in maize Authors
|Rocca, James -|
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: August 7, 2011
Publication Date: N/A
Technical Abstract: Phytoalexins are pathogen and insect-inducible biochemicals that are deployed to locally inhibit further biotic attack. Due its agronomic significance, maize has been extensively investigated for terpenoid-based defenses including insect-inducible terpene volatiles which function as indirect defenses through the attraction of predators and parasitoids of the offending herbivores. Unlike these low molecular weight volatile terpenes, the role of larger terpenoids in maize defense remains largely unknown. In response to stem attack by the European corn borer (Ostrinia nubilalis) and fungi, we observed the induced accumulation of six ent-kaurane-related diterpenoids, collectively termed kauralexins. Chromatographic isolation and NMR-based identification of the predominant Rhizopus microsporus induced metabolites revealed ent-kaur-19-al-17-oic acid and the novel analog ent-kaur-15-en-19-al-17-oic acid, assigned as kauralexin A3 and B3, respectively. Encoding an ent-copalyl diphosphate synthase, fungal-induced An2 transcript accumulation precedes highly localized kauralexin production which can eventually exceed 100 'g g-1 FW. Pharmacological applications of jasmonic acid and ethylene also synergize the induced accumulation of kauralexins. At concentrations as low as 10 'g ml-1, kauralexin B3 significantly inhibits the growth of the opportunistic necrotroph R. microsporus and the causal agent of anthracnose stalk rot, Colletotrichum graminicola. Kauralexins also exhibit significant O. nubilalis antifeedant activity. Our work establishes the presence of highly-inducible diterpenoid phytoalexin defense responses in maize and enables a more detailed analysis of the associated biosynthetic pathways, regulation and defense functions.