Geminiviruses constitute a group of plant viruses, with a ssDNA genome, whose replication in the nucleus of an infected cell requires the function of geminivirus-encoded replication initiator protein (Rep). Our results suggest that monoubiquitinated histone 2B (H2B-ub) promotes tri-methylation of histone 3 at lysine 4 (H3-K4me3) on the promoter of Chilli leaf curl virus (ChiLCV). We isolated homologues of two major components of the monoubiquitination machinery: UBIQUITIN-CONJUGATING ENZYME2 (NbUBC2) and HISTONE MONOUBIQUITINATION1 (NbHUB1) from N. benthamiana. ChiLCV failed to cause disease in NbUBC2-, and NbHUB1-silenced plants, at the same time, H2B-ub and H3-K4me3 modifications were decreased, and the occupancy of RNA polymerase II on the viral promoter was reduced as well. In further investigations, Rep protein of ChiLCV was found to re-localize NbUBC2 from the cytoplasm to the nucleoplasm, like NbHUB1, the cognate partner of NbUBC2. Rep was observed to interact and co-localize with NbHUB1 and NbUBC2 in the nuclei of the infected cells. In summary, the current study reveals that the ChiLCV Rep protein binds the viral genome and interacts with NbUBC2 and NbHUB1 for the monoubiquitination of histone 2B that subsequently promotes trimethylation of histone 3 at lysine 4 on ChiLCV mini-chromosomes and enhances transcription of the viral genes.

双生病毒是一组植物病毒，具有单链DNA基因组，其在受感染细胞核中的复制需要双生病毒编码的复制起始蛋白（Rep）的功能。我们的结果表明，单泛素化组蛋白 2B (H2B-ub) 促进辣椒曲叶病毒 (ChiLCV) 启动子上组蛋白 3 在赖氨酸 4 (H3-K4me3) 上的三甲基化。我们从N中分离出了单泛素化机制的两个主要组件的同源物：泛素结合酶 2 ( NbUBC2)和组蛋白单泛素化 1 ( NbHUB1 )。本塞米阿纳。 ChiLCV在NbUBC2和NbHUB1沉默的植物中未能引起疾病，同时H2B-ub和H3-K4me3修饰减少，RNA聚合酶II在病毒启动子上的占据也减少。在进一步的研究中，发现 ChiLCV 的 Rep 蛋白将 NbUBC2 从细胞质重新定位到核质，就像 NbUBC2 的同源伙伴 NbHUB1 一样。观察到 Rep 在受感染细胞的细胞核中与 NbHUB1 和 NbUBC2 相互作用并共定位。总之，目前的研究表明，ChiLCV Rep 蛋白与病毒基因组结合，并与 NbUBC2 和 NbHUB1 相互作用，实现组蛋白 2B 的单泛素化，随后促进 ChiLCV 微型染色体上赖氨酸 4 处的组蛋白 3 三甲基化，并增强病毒基因的转录。