|FOUNTAIN, JAKE - Louisiana State University|
|RARUANG, YENJIT - Louisiana State University|
|LUO, MENG - Louisiana State University|
|CHEN, ZHI-YUAN - Louisiana State University|
Submitted to: Physiological and Molecular Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2015
Publication Date: 4/15/2015
Citation: Fountain, J.C., Raruang, Y., Luo, M., Brown, R.L., Guo, B., Chen, Z-Y. 2015. Potential roles of WRKY transcription factors in resistance to Aspergillus flavus colonization of immature maize kernels. Physiological and Molecular Plant Pathology. 89:31-40.
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 examined the potential roles of six maize WRKY transcription factors in regulating defense responses against A. flavus. Along with the transcription factors, the expression of three defense genes were also examined in response to A. flavus inoculation in maize lines B73 (susceptible) and TZAR101 (resistant). Three of the transcription factors were found to be induced by fungal inoculation and constitutively expressed at higher levels in the resistant maize line. The expression of one of the defense genes was also induced by inoculation in the resistant line. This study indicates that these proteins may be important to resistance. Further studies may determine them to be useful to breeders as markers for transferring resistance to develop aflatoxin-resistant commercial corn. 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: Resistance to Aspergillus flavus by maize (Zea mays L.) is mediated by several defense proteins; however the mechanism regulating the expression of these defenses is poorly understood. This study examined the potential roles of six maize WRKY transcription factors, ZmWRKY19, ZmWRKY21, ZmWRKY53, ZmWRKY53.1, ZmWRKY67, and ZmWRKY68, in regulating defense responses against A. flavus. The expression of these WRKY transcription factors as well as three defense genes, Nonexpressor of Pathogenesis-Related Protein 1 (ZmNPR1), Pathogenesis-Related Protein 1 (ZmPR-1), and Ethylene Responsive Factor 1 (ZmERF1), were examined in response to A. flavus inoculation in maize lines B73 (susceptible) and TZAR101 (resistant). The genes ZmWRKY19, ZmWRKY53, and ZmWRKY67 were found to be induced by inoculation and constitutively expressed at higher levels in the resistant maize line. ZmWRKY19 and ZmWRKY53 are homologs of Arabidopsis WRKY53 and WRKY33, respectively, and may function in promoting antioxidant enzymes to sequester reactive oxygen species (ROS) during pathogen infection or abiotic stress. ZmWRKY67 is homologous to AtWRKY50 and may function in the suppression of jasmonic acid-regulated defenses in the resistant maize line. The expression of ZmNPR1 was also induced by inoculation in the resistant line without concurrent induction of ZmPR-1, possibly due to the observed induction of ZmERF1. These findings indicate that resistant maize lines may possess elevated oxidative stress tolerance potentially conferring resistance to programmed cell death as part of the hypersensitive response induced by ROS during necrotrophic pathogen infections. These findings provide a framework for future experiments examining maize resistance against A. flavus and other mycotoxin-producing fungi.