Regulation Of Sexual Development By The Histone Acetyltransferase GCN5 Is Mediated By A-to-I RNA Editing In Fusarium Graminearum

Fusarium head blight is a major fungal disease that affects China's grain yield and food safety.In addition to reducing wheat yield,it also accumulates mycotoxin DON in susceptible wheat,causing food quality and safety problems.Ascospores are the primary inoculum in the wheat scab.A recent study of our lab showed the occurrence of sexual stage-specific A-to-I RNA editing in F.graminearum.Interestingly,the stop codon TAG of 22%transcripts expressed by the well-known histone acetyltransferase gene GCN5 was changed to TGG by A-to-I editing during sexual development stage,resulting in translation read-through of GCN5.Therefore,GCN5 can both encode a normal size protein and a long protein that is extended by 50 amino acids during sexual stage.Histone acetyltransferase-mediated histone acetylation is an important mechanism of epigenetic modification.it can be involved in the regulation of gene transcription and silencing,chromatin condensation,DNA replication,stress response and many other cellular life processes.The long GCN5 proteins that are specifically generated during sexual stage are most likely to have some specific regulatory functions for sexual development.To investigate the function of A-to-I RNA editing with respect to the sexual development,we deleted the GCN5 gene in F.graminearum and found that the knockout mutants grew slowly,generated little aerial hyphae,and did not produced any conidia.The pathogenic capacity on wheat heads is totally lost.Moreover,the deletion mutants have serious defects in sexual development.They did not produce perithecia.Ectopic introduction of the wild-type GCN5 fragment(GCN5^TAG)into the mutant completely restored the defects of the?GCN5 mutant.introduction of the pre-edited GCN5 fragment(GCN5^TAA)alone recovered the defects in vegetative growth,sporulation and virulence but only partially restored the defects in sexual development.The complemented transformants produced perithecia but still had defects in ascus and ascospore formation and ascospore discharge.Introduction of the edited GCN5 fragment(GCN5^TGG)alone did not recover the defects in sexual development but partially restored the defects in asexual reproduction.To investigate the function of A-to-I RNA editing with respect to the histone acetylation,we analyzed the acetylation level of the wild-type GCN5^TAG complemented strain and the pre-edited GCN5^TAAAA complemented strain during sexual development.The results showed that the acetylation activity of the GCN5^TAA strain was higher than that of the GCN5^TAG strain.In addition,the GCN5^TAA short protein interacts strongly with Ada2 while the interaction of GCN5^TGG long protein with Ada2 is significantly reduced,indicating that loss of the stop codon editing can indeed regulate histone acetylation by affecting interactions between complex subunits.In summary,the A-to-I RNA editing at the stop codon of the GCN5 gene is involved in the regulation of the sexual development by directly affecting the interaction of GCN5 with other subunits and thereby affecting the acetylation activity of the SAGA complex in F.graminearum.This study will help to reveal the link between RNA editing and histone modification and provide a theoretical reference for effective prevention and control of wheat scab.