Digital gene expression analysis of early root infection resistance to Sporisorium reilianum f. sp. zeae in maize.

The maize smut fungus, Sporisorium reilianum f. sp. zeae, which is an important biotrophic pathogen responsible for extensive crop losses, can infect maize by invading the root during the early seedling stage. In order to investigate disease-resistance mechanisms at this early seedling stage, digital gene expression 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 genes in Huangzao4 and Mo17 were significantly differentially regulated at different infection stages. The glutathione S-transferase enzyme activity and reactive oxygen species 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 Huangzao4 and Mo17. These results suggest that the interplay between S. reilianum and maize during the early infection stage involves many important transcriptional and physiological changes, which offer several novel insights to understanding the mechanisms of resistance to the infection of biotrophic fungal pathogens.