P-110 - Beyond MFS1: the complex nature of multidrug resistance in Zymoseptoria tritici

Fungicide resistance in Zymoseptoria tritici, the causal agent of septoria leaf blotch in wheat, is an increasing concern in agriculture. Since the 2010s, strains exhibiting a ‘Multi-Drug Resistance’ (MDR) phenotype have been detected in the field. This phenotype is primarily linked to enhanced fungicide efflux through the overexpression of the membrane efflux pump gene MFS1, driven by three distinct insertions in its promoter (P_MFS1). More recently, a survey of Z. tritici populations in Northwestern Europe (2020–2021) suggested that additional mechanisms may be at play.

In this study we screened a sample of 380 strains for their P_MFS1 genotype and MDR phenotype. we identified extensive variability in the MFS1 promoter region of natural strains, some of which are linked to the MDR phenotype. A genome-wide association study (GWAS) also revealed that, beyond MFS1, other mutations and/or mechanisms are associated with MDR in Z. tritici field strains.

In addition to the analysis of field isolates, we characterized in vitro evolved MDR strains. Efflux assays showed increased efflux activity in most isolates compared to the ancestor, suggesting the involvement of additional transporters in the MDR phenotype. Other isolates exhibited distinct efflux phenotypes, pointing to entirely different MDR mechanisms. Whole-genome sequencing of the evolved strains identified novel candidate genes, including an uncharacterized AtrR-like transcription factor currently under investigation.