Analysis of Disease Resistance Induced by Ustilago maydis Strain with Overexpressed UM01240 Based on Transcriptome Sequencing

The objective of this study is to investigate the mechanism of maize resistance to corn smut disease induced by the secreted protein gene UM01240 of Ustilago maydis.

The wild-type strain SG200 of U. maydis, the UM01240 overexpression strain SG200-OE-UM01240, and the UM01240 deletion strain SG200ΔUM01240 were individually inoculated onto the maize variety Jidan209, which is highly susceptible to U. maydis. The three inoculated maize samples were named as S1, S2, and S3, respectively. After 7 d of inoculation, the pathogenicity differences among the tested strains on maize were evaluated. Using high-throughput RNA-Seq technology, the differential expression of genes between the S2 maize leaves and the S1 and S3 maize leaves was compared. Resistance-related genes involved in plant-pathogen interactions, flavonoid biosynthesis, phenylpropane metabolism, and plant hormone signal pathways were screened and subsequently validated through qRT-PCR.

The overexpression strain SG200-OE-UM01240 exhibited significantly reduced pathogenicity compared to the SG200 strain, with the corresponding maize sample S2 displaying the mildest leaf symptoms. In contrast, the SG200ΔUM01240 strain demonstrated significantly increased pathogenicity, with the maize sample S3 displaying the most severe leaf symptoms. In comparison to the S1 and S3 maize leaves, the S2 maize leaves exhibited 1 613 differentially expressed genes. Among these genes, 31 were associated with the plant-pathogen interaction pathway, primarily including protein-coding genes such as WRKY1, WRKY33, WRKY52, PR1, and PIT5. Additionally, 15 genes were linked to the flavonoid biosynthesis pathway, primarily including the synthesis of pinocembrin, naringenin, luteolin, and dihydroquercetin. Furthermore, 23 genes related to the phenylpropane metabolism pathway were identified, mainly associated with the synthesis of lignin, cinnamaldehyde, p-hydroxycinnamic acid, coniferylaldehyde, and sinapaldehyde. Lastly, 33 genes connected to plant hormone signal transduction pathways were also found, primarily concerning the synthesis of salicylic acid, cytokinins, gibberellins, and jasmonic acid. The results of qRT-PCR analysis for the selected genes were consistent with the transcriptome data.

The secreted protein gene UM01240 plays a crucial role in the pathogenicity of U. maydis in maize. The expression level of UM01240 is negatively correlated with the pathogenicity of U. maydis in maize. UM01240 achieves a balanced symbiotic relationship between U. maydis and the maize host by regulating pathways including plant-pathogen interaction, flavonoid and phenylpropanoid compound biosynthesis, and plant hormone signal transduction.