Environmental effects on resistance gene expression in milk stage popcorn kernels and associations with mycotoxin production

Authors: Dowd, Patrick; Johnson, Eric

Submitted to: Mycotoxin Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/24/2014
Publication Date: 12/19/2014
Publication URL: http://handle.nal.usda.gov/10113/60697
Citation: Dowd, P.F., Johnson, E.T. 2014. Environmental effects on resistance gene expression in milk stage popcorn kernels and associations with mycotoxin production. Mycotoxin Research. 31(2):63-82. DOI: 10.1007/S12550-014-0215-1.

Interpretive Summary: Mold toxin contamination of different types of corn causes health hazards to humans and animals and causes millions of dollars in losses. Insects contribute to the problem by damaging kernels. Popcorn typically has lower levels of these toxins than corn used for cattle feed under the same stress conditions, but the reasons for this are unknown. We analyzed expression of genes that code for proteins involved in resistance to ear mold and toxin production in popcorn kernels from three different years that were subject to different environmental stresses. As expected, expression of many resistance genes was reduced in years of heat or drought stress, but expression of some genes previously associated with resistance to the some ear mold toxins was unaffected. Insect damage altered the expression of resistance genes compared to undamaged ears. Expression of some genes was highly associated with mold toxin levels in the different years. This information can be used to guide the development of improved corn varieties, thereby reducing losses to mold and insects, and resulting in corn that is safer for humans and animals.

Technical Abstract: Like other forms of maize, popcorn is subject to increased levels of contamination by a variety of different mycotoxins under stress conditions, although levels generally are less than dent maize under comparable stress. Gene array analysis was used to determine expression differences of disease resistance associated genes in milk stage kernels from commercial popcorn fields over three years. Reduction in expression of resistance gene types was consistent for many previously identified resistance response associated genes, and included directly active enzymes such as chitinases, protease inhibitors and peroxidases; enzymes involved in the synthesis of cell wall barriers and secondary metabolites; and regulatory proteins. However, expression of several specific resistance genes previously associated with mycotoxins, such as aflatoxin in dent maize, was not affected. Insect damage altered the spectrum of resistance gene expression differences compared to undamaged ears. Correlation analyses showed expression differences of some previously reported resistance genes were highly associated with mycotoxin levels, and included glucanases, protease inhibitors, peroxidases and thionins.