Studies On The Molecular Mechanism Of Head Smut Resistance In Maize (Zea Mays L.)

The head smut fungus in maize, Sporisorium reilianum f. sp. zeae, which is an important biotrophic pathogen responsible for extensive crop losses, infects maize by invading the root during the early seedling stage. Head smut is not obvious until the tassels and ears emerge. S. reilianum has a very long life cycle that spans almost the entire developmental program of maize after the pathogen successfully invades the root.In order to investigate disease-resistance mechanisms at this early seedling stage, digital gene expression (DGE) analysis, which applies a dual-enzyme approach, was used to identify the transcriptional changes in the roots of Huangzao4(susceptible) and Mo17(resistant) after root inoculation with S. reilianum. During the infection in the roots, the expression pattern of pathogenesis-related (PR) genes in Huangzao4and Mo17were significantly differentially regulated at different infection stages. The glutathione S-transferase (GST) enzyme activity and reactive oxygen species (ROS) levels also showed changes before and after inoculation. The total lignin contents and the pattern of lignin depositions in the roots differed during root colonization of Huangzao4and Mo17.In order to understand how this pathogen interacts with the host during its long life cycle at the molecular level, and how this interaction differs between susceptible and resistant varieties of maize after hyphal invasion, the maize70mer-oligonucleotide microarrays were used to investigated transcriptional changes in the resistant maize line Mo17at four developmental stages. We found that there was a lengthy compatible relationship between the pathogen and host until the early8th-leaf stage. The resistance in Mo17relied on the assignment of auxin and regulation of flavonoids in the early floral primordium during the early floral transition stage. We propose a model describing the putative mechanism of head smut resistance in Mo17during floral transition. In the model, the synergistic regulations among auxin, flavonoids, and hyphal growth play a key role in maintaining compatibility with S. reilianum in the resistant maize line.