Unveiling the role of microRNAs in nonhost resistance to Sclerotinia sclerotiorum: Rice-specific microRNAs attack the pathogen via cross-kingdom RNAi.

Abstract

The development of rapeseed with high resistance against the pathogen Sclerotinia sclerotiorum is impeded by the lack of effective resistance resources within host species. Unraveling the molecular basis of nonhost resistance (NHR) holds substantial value for resistance improvement in crops. In the present study, small RNA sequencing and transcriptome sequencing were carried out between rice (a nonhost species of S. sclerotiorum) and rapeseed during infection, revealing the involvement of rice miRNAs on translation-related processes in both rice and the pathogen. Specifically, rice-specific miRNAs with potential capability for cross-kingdom RNAi against S. sclerotiorum were explored, of which Os-miR169y was selected as a representative case to elucidate its role in resistance to S. sclerotiorum. The silence of Os-miR169y decreased the resistance level of rice to S. sclerotiorum, and heterologous expression of Os-miR169y in Arabidopsis and rapeseed significantly enhanced the host resistance. The dual-luciferase reporter assay indicates that Os-miR169y targets S. sclerotiorum 60S ribosomal protein L19 (SsRPL19). Overexpressing Os-miR169y (OE_ss-miR169y) and RNAi of SsRPL19 (RNAi_ss-RPL19) in S. sclerotiorum significantly impaired the growth and pathogenicity of the pathogen, while overexpressing SsRPL19 exhibited a contrast effect. Yeast-two-hybridization revealed an interlinking role of SsRPL19 with multiple large and small ribosomal subunits, indicating its important role in translation. Proteome sequencing detected a decreased amount of proteins in transformants OE_ss-miR169y and RNAi_ss-RPL19 and significant suppression on key metabolic pathways such as carbon and nitrogen metabolisms. Collectively, this study suggests that rice can secrete specific miRNAs to suppress genes essential for S. sclerotiorum, such as Os-miR169y, which targets and suppresses SsRPL19 and thus impairs protein synthesis in the pathogen. This study sheds light on the intrinsic mechanisms of rice NHR against S. sclerotiorum, and further demonstrates the potential of using nonhost-specific "pathogen-attacking" miRNAs in improving resistance in host species.