Differential gene expression in kernels and silks of maize lines with contrasting levels of ear rot resistance after Fusarium verticillioides infection.

Fusarium verticillioides is the causal agent of ear rot in most maize-growing areas of southern Europe. F. verticillioides produces fumonisins commonly found at biologically significant concentrations in maize grain; the molecular interaction between the fungus and the plant is not well known, and little information is currently available about the defense response of maize against F. verticillioides infection. We attempted to identify genes that may be involved in Fusarium ear rot resistance using resistant and susceptible maize genotypes. Kernels of the resistant inbred showed significantly reduced incidence of infection by F. verticillioides, limited amounts of total fumonisin content and reduced fungal growth, as indicated by a lower copy number of β-tubulin 2 and FUM 21 genes of F. verticillioides. Gene expression data were obtained from microarray hybridizations using maize seeds infected with F. verticillioides, by comparing seeds at 0 and 48h after infection. Differentially expressed sequences were identified and classified into 11 functional categories. Most of the differentially expressed genes were assigned to the category "cell rescue, defense and virulence" in both resistant and susceptible maize lines. These genes encode for PR proteins, detoxification enzymes and β-glucosidases. Most of the pathogenesis-related genes were differentially activated after F. veticillioides infection, depending on the resistance level of the maize genotypes. In kernels of the resistant line, the defense-related genes assayed were transcribed at high levels before infection and provided basic defense against the fungus. In the susceptible kernels, the defense-related genes were induced from a basal level, responding specifically to pathogen infection. The qRT-PCR in infected silks showed that PR1, PR5, PRm6 and thaumatin genes had lower expression ratios in the resistant line compared to the susceptible one.