ARS | Publication request: Maize Kauralexins: inducible diterpenoid phytoalexins protect against fungal pathogens

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: February 23, 2011
Publication Date: N/A

Technical Abstract: Phytoalexins constitute a broad category of pathogen and insect-inducible biochemicals that locally protect plant tissues. In rice, a complex array of inducible diterpenoid phytoalexins constitute an important component of the plants anti-pathogen defenses. In contrast, despite the demonstration of fungal-induced ent-kaur-15-ene production in maize over 30 years ago, the identity of functionally analogous maize diterpenoid phytoalexins has remained elusive. In response to stalk damage by the European corn borer (Ostrinia nubilalis) and fungi, we observed the induced accumulation of six ent-kaurane-related diterpenoids, collectively termed kauralexins. Isolation and identification of the predominant 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. Fungal-induced An2 transcript accumulation precedes highly localized kauralexin production which can eventually exceed 100 'g g-1 FW. In maize, An2 gene encodes an ent-copalyl diphosphate synthase and thus exists as a logical candidate protein involved in the production of diterpenoid phytoalexin precursors. Consistent with other defenses, the combined application of jasmonic acid and ethylene synergize the induced accumulation of these phytoalexins. Kauralexins appear ubiquitous in maize and occur at high levels in the scutella of all inbred lines examined following seedling germination. At concentrations as low as 10 'g ml-1, kauralexin B3 significantly inhibited the growth of the opportunistic necrotroph Rhizopus microsporus and the causal agent of anthracnose stalk rot, Colletotrichum graminicola. Kauralexins also exhibited significant O. nubilalis antifeedant activity. Our work establishes the presence of highly inducible diterpenoid phytoalexin defenses in maize and enables a more detailed analysis of their biosynthetic pathways, regulation and crop defense function.