The Role of the ABC Transporter Gene PMR1 in Demethylation Inhibitor Resistance in Penicillium digitatum

In a previous study, we showed that disruption of the Penicillium digitatum ABC transporter gene PMR1 in a demethylation inhibitor (DMI)-resistant strain decreases its DMI resistance and that the level of constitutive expression of PMR1 in the DMIresistant strains was slightly higher than that in the sensitive strains. In this study, we carried out the following three experiments to investigate the specific role of PMR1 in DMI resistance: (i) disruption of PMR1 in a DMI-sensitive strain, (ii) sequencing of the PMR1 genes from DMI-sensitive and -resistant strains, and (iii) introduction of PMR1 under the control of a strong promoter or an intact inducible promoter into a PMR1disrupted strain and into a DMI-sensitive strain. Our findings suggest that a PMR1-based toxicant efflux mechanism for DMI resistance is present in both the DMI-sensitive and the DMI-resistant strains, and it might play a role in determining the baseline resistance of this fungus. A slight difference in PMR1 expression is not considered to be the factor that determines the difference in DMI resistance between the sensitive strains and the resistant strains.