The Role of Histone Methyltransferase SDG8 in Nitrate Signaling

SET Domain-containing Group 8 (SDG8) is a histone methyltransferase that mediates H3K36 methylation and affects gene expression level. Our study uncovered that SDG8 is required for plant responses to nitrate, a major form of nitrogen available to plants, across multiple scales ranging from genome-wide histone modification, transcriptome, RNA processing, root development, nitrate uptake, to primary metabolism. In response to nitrate level changes, plants change the H3K36me3 modifications at functionally relevant genomic loci, in a SDG8-dependent manner. Nitrate also induces preferential expression of gene isoforms, and the isoform shift is more prominent in the sdg8 mutant, indicating that SDG8 is required for canonical RNA processing. We showed that SDG8 regulates the isoform-specific expression of a putative transcription factor CCT101 in response to nitrate, and that CCT101 isoforms encode different proteins with distinct functions in transcriptional control. On a broad term, our study provides a framework to understand how chromatin modifications contribute towards effecting plant responses to environmental changes.含SET结构域的第8组组蛋白甲基转移酶（SET Domain-containing Group 8, SDG8）是一类介导H3K36甲基化并调控基因表达水平的酶类。本研究揭示，SDG8参与植物对硝酸盐的响应过程——硝酸盐是植物可获取的主要氮素形式，该研究覆盖了全基因组组蛋白修饰、转录组、RNA加工、根系发育、硝酸盐吸收以及初级代谢等多个尺度层面。当硝酸盐水平发生变化时，植物会在功能相关的基因组位点上以SDG8依赖的方式改变H3K36me3修饰。硝酸盐还可诱导基因转录本亚型的偏好性表达，且这种亚型转换在sdg8突变体中更为显著，表明SDG8对于经典RNA加工过程不可或缺。我们证实，SDG8在植物响应硝酸盐的过程中，调控假定转录因子CCT101的亚型特异性表达，且CCT101的不同转录本亚型编码功能各异的蛋白质，参与转录调控。总体而言，本研究为解析染色质修饰如何介导植物对环境变化的响应提供了一套研究框架。