Epigenetic modification is important for cellular functions. Trimethylation of histone H3 lysine 4 (H3K4me3), which associates with transcriptional activation, is one of the important epigenetic modifications. In this study, the biological functions of UvKmt2-mediated H3K4me3 modification were characterized in Ustilaginoidea virens, which is the causal agent of the false smut disease, one of the most destructive diseases in rice. Phenotypic analyses of the ΔUvkmt2 mutant revealed that UvKMT2 is necessary for growth, conidiation, secondary spore formation, and virulence in U. virens. Immunoblotting and chromatin immunoprecipitation assay followed by sequencing (ChIP-seq) showed that UvKMT2 is required for the establishment of H3K4me3, which covers 1729 genes of the genome in U. virens. Further RNA-seq analysis demonstrated that UvKmt2-mediated H3K4me3 acts as an important role in transcriptional activation. In particular, H3K4me3 modification involves in the transcriptional regulation of conidiation-related and pathogenic genes, including two important mitogen-activated protein kinases UvHOG1 and UvPMK1. The down-regulation of UvHOG1 and UvPMK1 genes may be one of the main reasons for the reduced pathogenicity and stresses adaptability of the ∆Uvkmt2 mutant. Overall, H3K4me3, established by histone methyltransferase UvKMT2, contributes to fungal development, secondary spore formation, virulence, and various stress responses through transcriptional regulation in U. virens.

Background Nitrogen (N) deposition is a key factor that affects terrestrial biogeochemical cycles with a growing trend, especially in the southeast region of China, where shortage of available phosphorus (P) is particularly acute and P has become a major factor limiting plant growth and productivity. Arbuscular mycorrhizal fungi (AMF) establish a mutualistic symbiosis with plants, and play an important role in enhancing plant stress resistance. However, the response of AMF to the combined effects of N deposition and P additions is poorly understood. Results Our results showed that N deposition significantly increased AMF root colonization rates and spore density, but inhibited both symbiotic relationship and spore propagation. In N-free plots, P addition significantly increased AMF root colonization rates, but did not significantly alter spore density. In low-N plots, AMF root colonization rates significantly decreased under low P addition, but significantly increased under high P addition, and spore density exhibited a significant decline under both low and high P additions. In high-N plots, AMF root colonization rates and spore density significantly increased under P additions. In general, AMF were closely related to the relative content of N and P in the soil. Interactive effects of simulated N deposition and P addition on both AMF root colonization rates and spore density were significant. AMF root colonization rates were significantly negatively correlated with soil moisture. Conclusions Moderate N deposition or P addition can weaken the symbiotic relationship between plants and AMF, significantly reducing AMF colonization rates and inhibiting spore propagation. However, a moderate addition of P greatly enhances spore yield. Soil moisture content is the main factor regulating AMF colonization rates. In the case of interactive effects, the AMF colonization rates and spore density are affected by the relative content of N and P in the soil.