Submitted to: Toxins
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/23/2011
Publication Date: 6/29/2011
Citation: Luo, M., Brown, R.L., Chen, Z., Menkir, A., Yu, J., Bhatnagar, D. 2011. Transcriptional profiles uncover Aspergillus flavus-induced resistance in maize kernels. Toxins. 3(7):766-786. Interpretive Summary: The fungus named Aspergillus flavus produces a poison called aflatoxin when it infects corn kernels. Aflatoxin prevents the corn from being used commercially. The best strategy for controlling this problem is to develop corn that is resistant to aflatoxin contamination. Towards this aim, we compared the expression of genes after kernel infection between a susceptible corn line and one that was resistant to aflatoxin contamination to identify the genes that are related to resistance; the resistant and susceptible lines used were selected because they are closely related which makes it easier to identify genes involved in resistance. Gene expression differences were detected between resistant and susceptible lines, noninoculated and inoculated kernels. Out of the genes identified may come useful markers which allow breeders to transfer resistance to commercial lines. This could lead to future savings of millions of dollars to growers, as a result of the elimination of aflatoxin contamination of corn.
Technical Abstract: Aflatoxin contamination caused by the opportunistic pathogen A. flavus is a major concern in maize production prior to harvest and during storage, and also a concern in many other crops, such as peanuts, cottonseed, tree nuts, and rice. Although a number of resistant maize lines with low aflatoxin contamination have been identified and used in resistant line development through traditional plant breeding, the level of resistance is not yet adequate to prevent unacceptable aflatoxin. Previous studies indicate that both constitutive and induced resistance is involved in maize kernel defense against A. flavus infection, however, little is known about the molecular mechanisms of mature kernels, the developmental stage susceptible to aflatoxin buildup, in response to fungal infection. In this research, maize oligonucleotide arrays were used to reveal the molecular response of maize kernels to the pathogen’s challenge. To decrease nonresistance-related differences in gene expression in resistant versus susceptible genotypic comparisons, two near isogenic maize lines varying in aflatoxin accumulation, Eyl25 (resistant) and Eyl31 (susceptible) were used. To avoid the environmental effects of field-based studies, a laboratory-based technique, the Kernel Screening Assay, which highlights mature kernel responses to infection, also was used. After 72 hours incubation of inoculated and noninculated mature kernels, gene expression profiles of the two lines were compared: 6955 genes in Eyl25 and 6565 in Eyl31 were detected in noninoculated kernels; 214 genes in Eyl25 and 2159 genes in Eyl31 were induced in inoculated kernels. Defense related genes and related regulation genes including signaling pathway and transcriptional factors were identified in both noninoculated and inoculated kernels. Comparisons of the resistant and susceptible lines indicate differences in gene expression, which may help us to understand the complex maize-A. flavus interaction. Genes identified in this study may serve as a useful resource for developing molecular markers to facilitate introgression of A. flavus resistance into commercially-useful maize backgrounds.