Transcription factor that regulates the expression of the gene cluster that mediates the biosynthesis of AAL-toxins, sphinganine-analog mycotoxins responsible for Alternaria stem canker on tomato by the tomato pathotype. 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. The CDCs are not essential for saprophytic growth but controls host-selective pathogenicity.