RNA-dependent RNA polymerases regulate ascospore discharge through the exonic-sRNA-mediated RNAi pathway

Authors: ZENG, WENPING - Huazhong Agricultural University; LIN, JING - Huazhong Agricultural University; XIE, JIATAO - Huazhong Agricultural University; FU, YANPING - Huazhong Agricultural University; LIN, YANG - Huazhong Agricultural University; CHEN, TAO - Huazhong Agricultural University; LI, BO - Huazhong Agricultural University; YU, XIAO - Huazhong Agricultural University; Chen, Weidong; JIANG, DAOHONG - Huazhong Agricultural University; CHENG, JIASEN - Huazhong Agricultural University

Submitted to: mBio
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/10/2024
Publication Date: 5/16/2024
Citation: Zeng, W., Lin, J., Xie, J., Fu, Y., Lin, Y., Chen, T., Li, B., Yu, X., Chen, W., Jiang, D., Cheng, J. 2024. RNA-dependent RNA polymerases regulate ascospore discharge through the exonic-sRNA-mediated RNAi pathway. mBio. 15: e00377-24. https://doi.org/10.1128/mbio.00377-24.
DOI: https://doi.org/10.1128/mbio.00377-24

Interpretive Summary: Plant pathogens such as Ascochyta rabiei and Fusarium graminearum go through sexual reproduction producing ascospores that serve as primary inoculum. Thus, ascospore production is very important for pathogenicity. The process of ascospore production is regulated by endogenous small interfering RNA-mediated RNA interference (RNAi). RNAi requires RNA-dependent RNA polymerases (RdRPs). This study uses F. graminearum as a model and investigated functions of five RdRPs (Fgrdrp1 through Fgrdrp5) using gene-deletion approach. Results showed that three (Fgrdrp1, Fgrdrp2 and Fdrdrp5) of the RdRPs play important roles in ascospore discharge, ascospore maturation and ascospore morphology, contributing to our understanding of the biological functions of Fgrdrps in sexual development of ascomycetes in general and in F. graminearum in particular.

Technical Abstract: Introduction: Ascospores, forcibly released into the air from perithecia formed on crop residues, are the primary inoculum for Fusarium head blight. During the sexual reproduction of Fusarium graminearum, endogenous small interfering RNAs-mediated RNA interference (RNAi) regulates ascosporogenesis. Objectives: Exploring the regulation mechanism of RNA-dependent RNA polymerases (RdRP), the components of conventional RNAi, during the sexual development of F. graminearum. Methods: We generated single deletion mutants of five Fgrdrps (Fgrdrp1 to Fgrdrp5), and compared the alterations in development and sexual reproduction with the wild- type strain. Performed sRNA and mRNA co-sequencing to analyze the changes in sRNA and mRNA in deletion mutants and performed a comparative analysis with sRNA of Fgdcl deletion mutant. Results: Based on functional genetics we found that three RdRPs, Fgrdrp1, Fgrdrp2 and Fgrdrp5, play important roles in ascospore discharge. 'Fgrdrp1 delays ascospore maturation, 'Fgrdrp2 leads to more ascospores scatter in perithecia, and 'Fgrdrp5 causes more two-celled immature ascospores. Deep sequencing and co-analysis of small RNA (sRNA) and mRNA reflected that these three RdRPs partly share their functions in the biogenesis and accumulation of exonic small interference RNA (ex- siRNA) and certain ex-siRNAs negatively regulate genes related to ascospore maturation or ascospore discharge. Comparing the sRNA sequencing data of Fgdcl deletion mutants, the ex-siRNA expression patterns in 'Fgrdrp1 and 'Fgrdrp2 were positively correlated with 'Fgdcl2 and 'Fgdcl1, respectively. In addition to sRNA, changes in expression levels of genes related to ABC transporters, glycogen and lipid metabolism, and transcription factors regulating sexual development may also be responsible for the defects in ascospore maturation or ascospore discharge of Fgrdrp deletion mutants. Conclusion: Our results verify the biological functions of Fgrdrps in sexual development and suggest that Fgrdrp1, Fgrdrp2 and Fgrdrp5 are the components of the ex-siRNA-mediated RNAi pathway during sexual reproduction in F. graminearum.