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

Unlabelled: Ascospores, forcibly released into the air from perithecia, are the primary inoculum for Fusarium head blight. In , the biological functions of four RNA-dependent RNA polymerases (RdRPs) () have been reported, but their regulatory mechanisms are poorly understood and the function of is still unknown. In this study, we found that in addition to and , also plays an important role in ascospore discharge, and they all participate in the generation of turgor pressure in a polyol-dependent manner. Moreover, these three genes all affect the maturation of ascospores. Deep sequencing and co-analysis of small RNA and mRNA certified that , , and partly share their functions in the biogenesis and accumulation of exonic small interference RNA (ex-siRNA), and these three RdRPs negatively regulate the expression levels of ex-siRNA corresponding genes, including certain genes associated with ascospore development or discharge. Furthermore, the differentially expressed genes of deletion mutants, those involved in lipid and sugar metabolism or transport as well as sexual development-related transcription factors, may also contribute to the defects in ascospore maturation or ascospore discharge. In conclusion, our study suggested that the components of the -dependent ex-siRNA-mediated RNA interference pathway include at least , , and .

Importance: We found that in addition to and , also plays important roles in ascospore maturation and ascospore discharge of . These three RNA-dependent RNA polymerases participate in the biogenesis and accumulation of exonic small interference RNA and then regulate ascospore discharge.