A virulent milRNA of Fusarium oxysporum f. sp. cubense impairs plant resistance by targeting banana AP2 transcription factor coding gene MaPTI6L

Fungi produce microRNA-like RNAs (milRNAs) with functional importance in various biological processes. Our previous research identified a new milRNA Foc-milR87 from Fusarium oxysporum f. sp. cubense, which contributes to fungal virulence by targeting the pathogen glycosyl hydrolase encoding gene. However, the potential roles of fungal milRNAs in interactions with hosts are not well understood. This study demonstrated that Foc-milR87 specifically suppressed the expression of MaPTI6L, a pathogenesis-related gene that encodes a transcriptional activator in the banana (Musa acuminata Cavendish group cv. ‘Baxi Jiao’) genome, by targeting the 3'untranslated region (UTR) of MaPTI6L. Transient overexpression of MaPTI6L activated plant defense responses that depend on its nuclear localization, yet co-expression with Foc-milR87 attenuated these responses. MaPTI6L enhanced plant resistance by promoting transcription of the salicylic acid (SA) signaling pathway marker gene MaEDS1. Sequence analysis of the MaPTI6L gene in 19 banana varieties, particularly those resistant to Fusarium wilt, uncovered single nucleotide polymorphisms (SNPs) at Foc-milR87 target sites. Experimental validation showed that these SNPs significantly reduce the microRNA's ability to suppress target gene expression. Our findings reveal that Foc-milR87 plays an important role in impairing plant resistance by targeting MaPTI6L mRNA and reducing MaEDS1 transcription during the early infection stage, suggesting the 3'UTR of MaPTI6L as a promising target for genome editing in generation of disease-resistant banana cultivars.