Transcription factor that regulates the expression of the gene clusters that mediate the biosynthesis of the host-selective toxins (HSTs) AF-toxins responsible for Alternaria black spot of strawberry disease by the strawberry pathotype (Probable). On cellular level, AF-toxins affect plasma membrane of susceptible cells and cause a sudden increase in loss of K(+) after a few minutes of toxin treatment (PubMed:22846083). Gene clusters encoding host-selective toxins (HSTs) are localized on conditionally dispensable chromosomes (CDCs), also called supernumerary chromosomes, where they are present in multiple copies (PubMed:12019223). The CDCs are not essential for saprophytic growth but controls host-selective pathogenicity (PubMed:12019223).