Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 11, 1999
Publication Date: N/A
Interpretive Summary: Corn, peanuts, cotton, and some tree nut crops are subject to infection by fungi of the genus Aspergillus. Infection results in the production of the highly carcinogenic compound aflatoxin B1. Regulations allow only very low levels of this compound in food and, therefore, lead to economic losses for growers when outbreaks of Aspergillus result in levels exceeding the acceptable limit. The objective of this research was to see if infection of maturing corn kernels by Aspergillus flavus, the species infecting corn, resulted in the production of proteins in the corn kernels which were not otherwise produced. We found that specific forms of two proteins were produced only by infected kernels. This means that the parts of the genes controlling expression of these proteins could be hooked to other proteins which are more toxic to the fungus to produce plants more resistant to infection by the fungus. These results will benefit corn breeders and companies developing corn lines with genetically engineered resistance to the fungus producing aflatoxin. The results should help increase the safety of food derived from corn and other crops subject to infection by this fungus.
Technical Abstract: Isoform patterns of chitinase and beta-1,3-glucanase of maturing kernels of yellow dent corn (Pioneer 3394) infected with Aspergillus flavus at the milk stage were investigated through polyacrylamide gel electrophoresis (PAGE). Proteins on the SDS gel with an apparent molecular weight range of 23-46 kDa were differentially present in the kernels infected with A. flavus. From in-gel (native PAGE) enzyme activity assays, three bands corresponding to chitinase isoforms and two bands corresponding to beta-1,3-glucanase isoforms were detected in the infected kernels. One chitinase isoform of 29 kDa was present only in the infected kernels, and another one of 28 kDa was present in both infected and non-infected kernels. They were acidic based on their migration on an acrylamide isoelectric focusing (IEF) gel. For the beta-1,3-glucanase, one isoform of 35 kDa was present in both infected and non-infected kernels, but another one, 33 kDa isoform, was present only in the infected kernels. Both acidic and basic beta-1,3-glucanase isoforms were detected in the IEF gel. The results of this study are the first to demonstrate patterns of enhanced or inducible proteins in maturing corn kernels in response to A. flavus infection at the milk stage. The results also indicate that only particular isoforms of the two fungal degradative enzymes are involved in the maturing corn kernels infected at the milk stage with A. flavus.