The pathogenesis-related maize seed (PRms) gene plays a role in resistance to Aspergillus flavus infection and aflatoxin contamination

Authors: Majumdar, Raj; Rajasekaran, Kanniah - Rajah; Sickler, Christine; Lebar, Matthew; Musungu, Bryan; FAKHOURY, AHMAD - Southern Illinois University; PAYNE, GARY - North Carolina State University; GEISLER, MATT - Southern Illinois University; Carter-Wientjes, Carol; Wei, Qijian - Mei Mei; Bhatnagar, Deepak; Cary, Jeffrey

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2017
Publication Date: 10/17/2017
Citation: Majumdar, R., Rajasekaran, K., Sickler, C.M., Lebar, M.D., Musungu, B.M., Fakhoury, A.M., Payne, G.A., Geisler, M., Carter-Wientjes, C.H., Wei, Q., Bhatnagar, D., Cary, J.W. 2017. The pathogenesis-related maize seed (PRms) gene plays a role in resistance to Aspergillus flavus infection and aflatoxin contamination. Frontiers in Plant Science. 8:1758. https://doi.org/10.3389/fpls.2017.01758.
DOI: https://doi.org/10.3389/fpls.2017.01758

Interpretive Summary: Fungi belonging to the genus Aspergillus are opportunistic pathogens to both humans and plants. In plants, Aspergillus flavus (A. flavus) infects several economically important crop species and produces aflatoxins that are potent carcinogens. Aflatoxins impose a serious threat to human/animal health and substantially reduce crop value. Maize is a major food and feed crop grown worldwide and aflatoxin contamination in maize is an utter concern. Host resistance against A. flavus is a major pre-harvest means of aflatoxin control in maize. Here we have explored the relative contribution of the maize pathogenesis-related (PR) protein, ZmPRms, in A. flavus resistance and aflatoxin production. Production of PR proteins in response to biotic stressors at the infection site serves as a first line of defense and contribute to systemic acquired resistance (SAR) in plants. Among different PR proteins reported in maize, ZmPRms, has been shown to be highly induced in the kernels upon A. flavus infection. We therefore used a RNA interference (RNAi)-based gene silencing approach to inhibit the expression of ZmPRms specifically in the kernels to understand the relative contribution of this gene in A. flavus resistance and aflatoxin production. Reduced expression of ZmPRms in transgenic maize kernels significantly increased A. flavus infection and resulted in a several fold higher accumulation of aflatoxins than the control plants. The work presented here functionally validates the importance of a major seed pathogenesis related protein, PRms, in aflatoxin resistance. The results presented here are promising and the knowledge obtained from this study might help us to develop A. flavus resistant maize varieties in future and reduce aflatoxin contamination.

Technical Abstract: Aspergillus flavus is an opportunistic plant pathogen that colonizes and produces the toxic and carcinogenic secondary metabolites, aflatoxins, in oil-rich crops such as maize (Zea mays ssp. mays L.). Pathogenesis-related proteins serve as a first line of defense against invading pathogens by conferring systemic acquired resistance (SAR) in plants. Among these, production of the maize pathogenesis-related protein, ZmPRms, has been shown to be involved in resistance to infection by A. flavus and other pathogens. To better understand the relative contribution of ZmPRms to A. flavus resistance and aflatoxin production, a seed-specific RNA interference (RNAi)-based gene silencing approach was used to develop transgenic maize lines expressing hairpin RNAs to target ZmPRms. Down-regulation of ZmPRms in transgenic kernels resulted in a ~250-350% increase in A. flavus infection accompanied by a ~4.5 to 7.5-fold higher accumulation of aflatoxins than control plants. Gene co-expression network analysis of RNA-Seq data during the A. flavus-maize interaction identified ZmPRms as a network hub possibly responsible for regulating a number of downstream candidate genes associated with disease resistance and other biochemical functions. Expression analysis of these candidate genes in the ZmPRms-RNAi lines demonstrated down-regulation (vs. control) of a majority of these ZmPRms regulated genes during A. flavus infection. These results are consistent with a central role of ZmPRms in resistance to A. flavus infection and aflatoxin accumulation in maize kernels.