Genome-wide mapping of H3K4 tri-methylation in ΔUvkmt2 mutant strain of Ustilaginoidea virens. Genome-wide mapping of H3K4 tri-methylation in ΔUvkmt2 mutant strain of Ustilaginoidea virens

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. In particular, H3K4me3 modification involves in the transcriptional regulation of conidiation-related and pathogenic genes. 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 stresses response through transcriptional regulation in U. virens. Overall design: Examination of H3K4 tri-methylation of ΔUvkmt2 mutant strain of Ustilaginoidea virens. Two biological replicates were performed.

表观遗传修饰（epigenetic modification）对于细胞功能至关重要。组蛋白H3赖氨酸4三甲基化（trimethylation of histone H3 lysine 4，H3K4me3）与转录激活过程相关，是一类重要的表观遗传修饰。本研究以引发稻曲病（该病害为水稻最具破坏性的病害之一）的病原菌绿核菌（Ustilaginoidea virens）为研究对象，解析了UvKmt2介导的H3K4me3修饰的生物学功能。
对ΔUvkmt2突变体的表型分析显示，UvKMT2是绿核菌生长、产孢、次生孢子形成以及致病力所不可或缺的因子。免疫印迹（immunoblotting）与染色质免疫共沉淀测序（chromatin immunoprecipitation assay followed by sequencing，ChIP-seq）实验结果表明，UvKMT2是H3K4me3建立所必需的，该修饰覆盖绿核菌基因组中的1729个基因。尤为关键的是，H3K4me3修饰参与了产孢相关基因与致病基因的转录调控。UvHOG1与UvPMK1基因的下调表达，可能是ΔUvkmt2突变体致病力与胁迫适应性下降的主要原因之一。
综上，由组蛋白甲基转移酶UvKMT2催化建立的H3K4me3修饰，可通过转录调控途径参与绿核菌的真菌发育、次生孢子形成、致病力调控以及各类胁迫应答。
实验整体设计：对绿核菌ΔUvkmt2突变体菌株的H3K4三甲基化水平进行检测，共设置2个生物学重复。