Expression of microRNA‐like RNA‐2 (Fgmil‐2) and bioH1 from a single transcript in Fusarium graminearum are inversely correlated to regulate biotin synthesis during vegetative growth and host infection

MicroRNA‐like RNAs (milRNAs) post‐transcriptionally down‐regulate target genes. We investigated Fusarium graminearum (Fg) milRNA expression during fungal vegetative growth and infection of wheat. Small RNA sequencing identified 36 milRNAs from Fg, one of which, Fgmil‐2, had >100 transcripts per million in conidia, mycelia and infected wheat, with the highest expression in conidia and the lowest expression in colonized wheat tissue. Fgmil‐2 displays perfect homology to the 3ʹ‐untranslated region (3ʹ‐UTR) of an FgbioH1 messenger RNA that is involved in biotin biosynthesis. Poly(A) polymerase‐mediated rapid amplification of cDNA ends combined with sequencing analysis demonstrated that cleavage at a specific site by FgDicer2 in the 3ʹ‐UTR of FgbioH1 transcripts generated the Fgmil‐2 precursor with a typical hairpin structure. Deletion of FgbioH1 or FgDicer2 genes abolished Fgmil‐2 biogenesis. FgbioH1 had an inversely correlated pattern of expression to that of Fgmil‐2 and FgDicer2. Deletion of FgbioH1 also showed that it is required for mycelial growth, virulence, mycotoxin biosynthesis and expression of biotin‐dependent carboxylase genes. This study reveals in Fg a novel mode of inversely correlated post‐transcriptional regulation in which Fgmil‐2 originates from its own target transcript, FgbioH, to govern biotin biosynthesis.