Advances in the Development of Host Resistance in Corn to Aflatoxin Contamination by Aspergillus flavus

Abstract

Aflatoxins are toxic, highly carcinogenic secondary metabolites of Aspergillus flavus and A. parasiticus, which when produced during fungal infection of a susceptible crop in the field or after harvest contaminate food and feed and threaten human and animal health. Although there are several management strategies that may reduce aflatoxin contamination of corn, the preeminent strategy for elimination of aflatoxin is to develop preharvest host resistance to aflatoxin accumulation. This strategy has gained even greater prominence due to recent discoveries of natural resistance in corn that can be exploited in plant-breeding strategies. The ability to identify resistant corn genotypes has been enhanced by the development of a laboratory kernel-screening assay and by a strain of A. flavus genetically engineered to produce beta-glucuronidase, an enzyme whose activity can be monitored to assess the degree of fungal infection in kernels. Investigations of resistant corn genotypes have associated kernel pericarp wax characteristics with resistance, identified kernel proteins associated with resistance to and inhibition of fungal growth or aflatoxin biosynthesis, and identified chromosome regions associated with resistance to Aspergillus ear rot and aflatoxin production. Such research advances could lead, in the near future, to commercially available, agronomically acceptable corn lines with multiple preharvest resistances to aflatoxin contamination.

Using biotechnology to enhance host resistance to aflatoxin contamination of corn

“…(reviewed in Brown et al, 1999). The results of these studies indicate the presence of two levels of resistance: at the pericarp and at the subpericarp level.…”

“…With corn, the strategy of enhancing host resistance to aflatoxin contamination through breeding has gained prominence because of: 1) the successful identification of germplasm resistant to aflatoxin contamination, and 2) the significant advances in the identification of natural resistance mechanisms and traits (Brown et al, 1999;Cleveland et al, 2003). However, these investigations indicated that resistance to aflatoxin contamination involves multiple chromosome regions and several genes .…”

“…Therefore, research is needed to elucidate the biochemical mechanisms that confer resistance in corn kernels that are vulnerable to aflatoxin contamination. These resistance mechanisms could then be used to enhance germplasm through marker-assisted breeding and/or genetic engineering (reviewed in Brown et al, 1999). Gaining an understanding of the natural resistance mechanisms in corn could serve as "nature's lesson" about the specific requirements for seed-based resistance against fungal attack.…”

AMELIORATION DES PLANTES Biotechnologies et arachide

“…Le principal résultat publié sur l'arachide concerne une étude histologique de l'infection réalisée in situ grâce à un transformant de A. parasiticus utilisant comme promoteur un précurseur de l'aflatoxine, le gène Nor-1 [29]. Sur le maïs, des transformants A. flavus-GUS ont permis d'évaluer la croissance et le degré de l'infestation fongique [30] dans les graines et d'analyser l'expression des gènes reliés à l'aflatoxine [31].…”

Identifying Aflatoxin Resistance-related Proteins/Genes through Proteomics and RNAi Gene Silencing1

“…The approach to enhance host resistance through conventional breeding and/or genetic engineering has gained renewed attention following the discovery of natural resistance to A. flavus infection and aflatoxin production in maize (Gardner et al, 1987;King and Scott, 1982;Widstrom et al, 1987;Scott and Zummo, 1988;White, 1995, Brown et al, 1995;Brown et al, 1999). Promising sources of resistant peanut germplasm have also been identified from a core germplasm collection, although resistance screening has proven to be a difficult task with this crop (Holbrook et al, 2008).…”