Molecular Approaches to Study Temporal and Spatial Regulation of Maize Gene Expression during Fungal Infection

Aspergillus flavus and Fusarium verticillioides are fungal pathogens that cause maize ear rots and produce mycotoxins. Pathogenesis and host response during infection of kernels by these two fungi remain poorly understood. To gain a better understanding of the host-parasite interactions between maize kernels and these two fungi, we monitored transcriptome changes, colonization and tissue-specific gene expression of developing maize kernels inoculated with each fungus. Comparative transcriptomics studies showed a set of genes that were similarly expressed in both interactions, indicating a conserved response to fungal infection. Histological studies revealed that both fungi colonized the aleurone, endosperm and embryo of maize kernels, but the pattern of colonization by the two fungi differed. RNA in situ hybridization and qRT-PCR analysis showed that maize PRms (Pathogenesis related protein, maize seeds) was induced in the aleurone and scutellum during infection of these two fungi. However, Sh1 (Shrunken-1) was expressed in the embryo before fungal infection, and it was induced in the aleurone and scutellum by these two fungi. By comparing histological and in situ hybridization results in adjacent serial sections, we found that these two genes were expressed in the tissue in advance of hyphal invasion. The results indicate the existence of unique as well as shared defense responses in maize kernel during the early infection by A. flavus and F. verticillioides. Our studies provide a clearer understanding of these interactions and position us to identify resistance genes for crop improvement.