PdMLE1, a specific and active transposon acts as a promoter and confers Penicillium digitatum with DMI resistance

Previously, we found a 199bp element which inserted into the promoter of PdCYP51B gene in Penicillium digitatum, was associated with the overexpression of this gene and DMI fungicides resistance. However, the mechanism how this 199bp element upregulate the expression of downstream gene was completely unknown. In the current study, we confirmed that this 199bp element was a MITE-like element, designated as PdMLE1. blast searching and Southern blot showed that this 199bp element was unique to P.digitatum. Genome-wide localization of PdMLE1 showed that it preferentially inserted into A+T rich regions, and several copies localized at the coding or regulation regions of genes were found. Penicillium digitatum mutant harbouring the PdMLE1 fused GFP gene showed the strong green fluorescence, indicating the powerful promoter activity of PdMLE1. By promoter deletion method, we identified a 20bp core sequence in PdMLE1 which was associated with its promoter activity. In addition, we also limited the core element of PdCYP51B promoter to a 368bp region. Collectively, we proposed a model that PdMLE1 acted as a powerful promoter and most likely recruited the transcription factor(s), therefore led to the overexpression of PdCYP51B gene and conferred P.digitatum with DMI resistance. This is the first regulation model of transposon resulted fungicide resistance proved in plant pathogens.