The Function Of FgRID1 In Sexual Development And Repeat-induced Point Mutation Is Activated By A-To-I RNA Editing In Fusarium Graminearum

Fusarium head blight?FHB?is a worldwide epidemic disease of crops.Not only can FHB cause yield and qualityreduction of wheat,but mycotoxins produced by Fusarium graminearumcanthreaten the food safety and harm the health of human and animals.F.graminearum is a major pathogenic filamentous fungus of the FHB,and its ascospores in sexual period are important primary infection sources.Researches in the sexual development of F.graminearum contribute to reveal the features of FHB and provide theoretical reference for control measures.Studies about the PUK1-like genes edited by A-to-I RNA editing showed that editing events also occurred in the RID1 homologue FGRRES₀8648 which encodes a DMT?DNA methyltransferase?protein and regulates the RIP?Repeat-induced point mutation?mechanism.RIP is a genome defensive mechanism in filamentous fungi which can induce transition mutations from C:G to T:A base pairs within the regions of repetitive DNA during the sexual stage of the fungal life-cycle,thus maintaining the genome stable.Previous research in Neurospora crassa showed that RIP defective 1?RID1?is responsible for RIP.In Fusarium graminearum,the RID1 homologue?FGRRES₀8648?is a pseudogene encoding a truncated protein.During sexual stage,the advaced stop codon UA⁶⁴⁴G is subjected to A-to-I RNA editing and turn to be UG⁶⁴⁴G,thus expressing the full length protein.This indicates that RNA editing and RIP mechanism both occurring in sexual stage may have some close relationships.To find this potential relationship,we deleted FgRID1 gene in F.graminearum and failed to detect any obvious phenotypes in vegetative growth,conidiation,plant infection and DON production.However,in sexual stage,the mutant produces normal perithecia in comparision with the wild type PH-1,and showed a defect in perithecia amount and ascospore release.A large amount of abnormal ascospores with different shapes was observed late in sexual stage,indicating that FgRID1 plays a crucial role in ascospores development and discharge.The edited form but not the truncated form of FgRid1 recovered the defects of mutant,indicating that RNA editing affects the sexual development by directly controlling the expression of FgRID1.In addition,our research also showed that FgRid1 was essential for RIP by constructing two tandem hph?hygromycin phosphotransferase?genes and transforming the PH-1 to detect the RIP.Also,we deleted the sequence behind the premature stop codon UA⁶⁴⁴G of the FgRID1 and found that some of the ascospores didn't have RIP,suggesting that A-to-I RNA editing may involve in regulating RIP in F.graminearum and other hypocrales species.The meaning of our research is that it will contribute to reveal the relationship between the two epigenetic mechanism—A-to-I RNA editing and RIP.Additionnally,our research will help to lay a theoretical foundation for further studying the complex regulation in sexual development of filamentous fungi.