Plasticity of the MFS1 promotor is not the only driver of Multidrug resistance in Zymoseptoria tritici

Background Multidrug resistance has been identified in the fungal pathogen responsible for Septoria leaf blotch, Zymoseptoria tritici, since 2011. It has been linked to the overexpression of the gene encoding the MFS1 transporter due to inserts in the promoter region of MFS1 (PMFS1), namely types I-III. Recently, two new inserts were discovered in PMFS1 that were not linked to MDR, interrogating about whether PMFS1 inserts are the only drivers of MDR in Z. tritici. The goal of our study was to gain a more complete view of MDR in Z. tritici by examining the genotypic diversity associated with the MDR phenotype in a large sample of the modern population. Results We isolated 384 potential MDR strains between 2020 and 2021 in northern Europe for PMFS1 genotype and MDR assessment. We discovered six new inserts in PMFS1, bringing the total count to 13 including one insertion-deletion in the 5' UTR region. Of these, 11 display similarities with transposable elements, and 3 are not linked to MDR. Some field strains were significantly more resistant than their respective reference of the same PMFS1 genotype and some strains without insert displayed MDR phenotype. Conclusion We described the landscape of the MDR in modern Z. tritici population and postulate that PMFS1 is a hotspot for insertions involving transposition events. Our study shows that MDR cannot be solely explained by inserts found in PMFS1, and that additional mechanisms might be at work. ### Competing Interest Statement The authors have declared no competing interest.