A-to-I RNA编辑调控禾谷镰刀菌组蛋白乙酰化和有性生殖的分子机制

Fusarium head blight (FHB) caused by Fusarium graminearum is one of the most devastating disease of wheat and barley, which seriously affects grain yield and food safety. Sexual reproduction is a crucial component of head blight epidemiology, as forcibly discharged ascospores serve as the primary inoculum. Acetylation of histones is a key epigenetic regulatory mechanism of gene expression in eukaryotes. It plays pivotal roles in the development and adaptation of fungi. Recently we reported A-to-I RNA editing, a novel epigenetic mechanism in sexual reproduction of F. graminearum. Intriguingly, the stop codon UAG of many subunits of SAGA and Rpd3L/S complexes that are important for histone acetylation function is changed by A-to-I RNA editing to amino acid codon UGG (stop-loss editing), resulting in the addition of an extra stretch of peptides to the C terminus of proteins. In this project, we will identify the stop-loss editing in the subunits of both SAGA and Rpd3L/S complexes that have a significant impact on the sexual reproduction and histone acetylation. Furthermore, we intend to uncover the mode of the stop-loss editing to affect histone acetylation. We will also reveal the role of the stop-loss editing one the transcriptional control of sexual stage-specific expressed genes. Overall, results from proposed project will illuminate the regulatory mechanism of histone acetylation and sexual reproduction by A-to-I RNA editing and be helpful to develop new disease control strategy by targeting sexual reproduction of Fusarium graminearum.

禾谷镰刀菌引起的小麦赤霉病是影响我国粮食产量和食品安全的重大真菌病害，其有性生殖产生的子囊孢子是病害发生的初侵染源，对赤霉病发生流行至关重要。已知组蛋白乙酰化是真核生物中广泛存在的一种表观遗传调控机制，对真菌生长发育和适应性具有重要作用。申请人课题组前期在禾谷镰刀菌有性生殖阶段发现了一种新的表观遗传调控机制：A-to-I RNA编辑，该机制导致组蛋白乙酰化修饰相关的SAGA和Rpd3L/S复合体中多个亚基的mRNA上终止密码子UAG转变为氨基酸密码子UGG，产生一种延长蛋白，此类编辑称为终止密码子丧失编辑。本项目拟验证SAGA和Rpd3L/S复合体亚基mRNA上影响有性生殖和组蛋白乙酰化的终止密码子丧失编辑，探究其调控组蛋白乙酰化的途径，明确其与有性阶段特异表达基因转录调控之间的关系，最终揭示其调控组蛋白乙酰化和有性生殖的分子机制，为发展针对有性生殖的新病害防控策略提供科学依据。

禾谷镰刀菌引起的小麦赤霉病是影响我国粮食安全和人畜健康的重大真菌病害，其有性生殖产生的子囊孢子是病害发生的初侵染源，对赤霉病发生流行至关重要。申请人课题组前期发现禾谷镰刀菌有性生殖阶段存在A-to-I RNA编辑现象，许多基因的终止密码子UAG经RNA编辑后转变为氨基酸密码子UGG，产生一种延长蛋白，此类RNA编辑称为终止密码子丧失编辑。本项目通过定点突变技术对组蛋白乙酰基转移酶SAGA复合体6个基因（GCN5，NGG1，SPT7，TAF9，TAF6，SGF73）和组蛋白去乙酰化酶Rpd3L/S复合体3个基因（RPD3，SIN3，PHO23）的终止密码子丧失编辑进行了功能验证，发现GCN5的终止密码子丧失编辑对有性生殖具有重要作用，非编辑形式突变体GCN5TAA子囊孢子形成出现缺陷，而编辑后形式突变体GCN5TGG菌落生长较慢，不能产生子囊壳。进一步通过蛋白杂交、酵母双杂和ChIP-seq实验证明编辑后的Gcn5蛋白与Ada2的互作能力下降，组蛋白H3K9AC和H3K27AC水平下降，揭示了终止密码子丧失编辑调控组蛋白乙酰化的途径。本项目通过ChIP-seq实验分析了禾谷镰刀菌有性生殖时期H3K14AC、H3K9AC、H3K27AC、H3K56AC、H4K5AC的修饰谱，证明H4K5AC、H3K9AC、H3K27AC对有性生殖特异的基因表达贡献最大，最终揭示了A-to-I RNA编辑通过调控组蛋白乙酰化实现对有性生殖调控的重要意义。