Submitted to: Phytopathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/1/2005
Publication Date: 2/1/2006
Citation: Chen, Z.-Y, Brown, R.L., Rajasekaran, K., Damann, K.E., Cleveland, T.E. 2006. Identification of a Maize Kernel Pathogenesis-Related Protein and Evidence for its Involvement in Resistance to Aspergillus flavus Infection and Aflatoxin Production. Phytopathology. 96(1):87-95. Interpretive Summary: Aflatoxins are poisons produced by the fungus, Aspergillus flavus, after it infects agricultural commodities, such as corn. Contamination of corn with aflatoxins causes financial loss to growers and is a potential health hazard to animals and humans. An important strategy for controlling aflatoxin contamination of corn involves identifying resistance genes to aid in developing corn lines that resist aflatoxin production. Recently, a corn kernel protein was determined to be present at higher levels in resistant corn lines than in susceptible ones. This protein was found in laboratory tests to destroy Aspergillus flavus RNA and to inhibit fungal growth. Tobacco plants that were genetically engineered to over-produce this protein also exhibited destruction of Aspergillus flavus RNA and inhibited fungal growth. In another experiment, the gene encoding this protein was expressed higher in resistant corn ears than in susceptible ones after fungal infection. These results show that this protein may play an important role in corn resistance against Aspergillus flavus growth and aflatoxin contamination. Enhancing the expression of this protein in commercially-useful corn lines could result in the development of lines that resist aflatoxin contamination. This would, in turn, enhance the safety of feed and food for animals and humans, and increase financial savings to growers.
Technical Abstract: Aflatoxins are carcinogens produced by Aspergillus flavus and A. parasiticus during infection of susceptible crops such as maize. Several resistant maize genotypes have been identified and the kernel proteins have been suggested to play an important role in resistance. Through comparisons of kernel endosperm proteins of resistant and susceptible genotypes separated using 2-D gels, several protein spots were found to be unique or upregulated in resistant genotypes in a previous study. In the present study, one of such upregulated protein spots (#717) was sequenced and identified as a pathogenesis-related protein (PR-10) based on its sequence homology. To assess the relationship of this PR-10 protein (MzPR-10) to host resistance of maize against fungal infection and aflatoxin production, the corresponding cDNA (pr-10) was cloned from an endosperm cDNA library. It encodes a protein of 160 aa with a predicted molecular mass of 16905 Da and an isoelectric point of 5.38. The expression of pr-10 during kernel development increased five-fold between 7-22 days after pollination, and is induced upon A. flavus infection in the resistant genotype. This pr-10 gene has also been introduced into both E. coli and tobacco for in vitro and in vivo studies. The MzPR-10 over-expressed in E. coli exhibited a ribonucleolytic activity and antifungal properties. The leaf extracts of transgenic tobacco plants expressing maize pr-10 gene also demonstrated RNase activity and inhibitory effect on A. flavus growth in vitro. These evidences suggest MzPR-10 may play a direct role in kernel resistance by inhibiting fungal growth of A. flavus.