Infection of maize kernels by Aspergillus flavus, a pathogen of maize, results in kernel deterioration and contamination with aflatoxin. To identify putative pathogenicity genes, a custom-designed Affymetrix GeneChip DNA microarray was used to follow gene expression in A. flavus during infection of maize kernels in the field. Nearly 1,500 fungal genes were more highly expressed in infected living kernels when compared to expression in colonized autoclaved kernels at the same developmental stage. Of these, nepA was expressed on average 8 times higher in living kernels. nepA belongs to the necrosis inducing protein superfamily (NPP1), which several members in other plant pathogens are known to be involved in pathogenicity. To determine if nepA has a role in pathogenicity, the gene was deleted, and the mutant was used in pathogenicity tests. Growth and conidiation of the mutant on the kernel surface appeared sporadic and varied. In contrast, consistent differences in growth within kernels were observed between the mutant and wildtype . The nepA deletion mutant appeared to be impeded in growth in the endosperm, while wild type caused necrosis of kernel tissues. Additional experiments are being performed with beta-glucuronidase- expressing strains and histological stains to better define mycelium within kernel tissues. Our initial findings suggest that nepA has a role in the pathogenicity of A. flavus.
Full conference title:
6th International Aspergillus Meeting
- Asperfest 6 (2009)