Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 10/25/2004
Publication Date: 2/1/2005
Citation: Camas, A., Lopez, L., Gardner, H.D., Brooks, T.D., Windham, G.L., Williams, W.P. 2005. Expression of different lipoxygenase genes in relation to resistance in corn developing and mature embryos to aflatoxin contamination by Aspergillus flavus [abstract]. Proceedings 2004 4th Annual Fungal Genomics, 5th Annual Multi-Crop Fumonisin Elimination and 17th Annual Multi-Crop Aflatoxin Elimination Workshops. p. 72.
Technical Abstract: The accumulation of aflatoxin, a mycotoxin produced by the fungus Aspergillus flavus (A. flavus) Link: Fr., during maize grain fill continues to be a problem. The impact of aflatoxins on the agricultural economy and human and animal health is well established. Because most aflatoxin problems develop in the field, the best strategy for eliminating mycotoxin production is to develop preharvest host resistance to aflatoxin contamination. Developing natural genetic resistance should be the most effective control for aflatoxin production in maize and is currently used for the development of resistant hybrids in conventional plant-breeding programs. USDA-ARS scientists at Mississippi State, Mississippi have contributed to this intense field research by releasing several corn inbreds as a source of resistance to kernel infection by A. flavus. However, incorporating resistance from these sources into commercial hybrids requires identification and characterization of factors shown to be associated with resistance. The ability to identify resistant corn genotypes has been enhanced by the combination of genomic analysis and molecular biology tools. Molecular markers associated with resistance would help to advance the breeding program and provide clues about the mechanisms of resistance. Therefore, working in this direction we have found that a Lipoxygenase could be a molecular marker consistently associated with corn resistance. Lipoxygenases are enzymes responsible for initiating the octadecanoid pathway in response to insect and fungi attack. We compared lox expression levels of two different genes (13-lox and 9-lox) of immature embryos from different resistant and susceptible inbreds and of mature embryos from six crosses among the same resistant and susceptible genotypes. We sampled at different time points after inoculation with A. flavus spores. We found that 13-Zmlox gene expression in developing and mature embryos, appears to be associated with the corn resistance response to A. flavus attack. This gene codes a 13-LOX isoform that acts on linoleic acid producing 13(S)-hydroperoxides and its derivatives could also function as inhibitors of sporulating factors and Aflatoxin gene synthesis in A. flavus. 13-lox expression analysis showed higher expression in resistant genotypes than in susceptible genotypes, whereas inoculated embryos showed higher expression than the non-inoculated controls. Similar results were obtained using mature embryos from the hybrids between resistant and susceptible inbreds. We did not detect any 13-lox expression in hybrids obtained from the cross between susceptible inbred lines. Furthermore, the level of aflatoxin content measured in infected kernels from resistant and susceptible genotypes showed good correlation with 13-lox expression levels. Although resistance to contamination by aflatoxin is greatly influenced by environmental effects on the plants, the differences in lox expression between hybrid genotypes could be related to the inherited plant resistant mechanisms. Therefore, we propose the use of this corn embryo 13-lox gene as a potential molecular marker that could contribute to get commercially available and agronomically acceptable corn lines.