Mating-Type Locus Control of Cell Identity

Abstract

This chapter addresses how MAT loci is identified from budding ascomycetes to filamentous ascomycetes to basidiomycetes function to specify cell identity. The chapter begins with an introduction to the cell identity determination paradigm established in the budding yeast Saccharomyces cerevisiae. It explores how cell identity determination affects sexual reproduction in basidiomycetes. Through these examples, we see how cell identity determination lays the foundation for effective sexual reproduction and survival across diverse fungi. In S. cerevisiae, a single-celled ascomycete, growth can take place either clonally through haploid cell budding, or sexually through mating followed by meiosis. For most ascomycetes, the precise mechanisms by which these transcriptional regulators specify cell identity is not known; however, MAT control in S. pombe is explored in more detail. An ascomycete in which cell identity determination has been studied in detail is the human fungal pathogen Candida albicans. A detailed expression analysis determined the transcriptional profiles of cells with targeted deletions of the MTL regulator components in every possible combination in both the white and opaque phases. Control of cell identity by the MAT locus in basidiomycetes expands the simple transcription factor-encoding locus seen in ascomycetes to a more complex structure. The fate of fused hyphae is determined by the interactions of the homeodomain proteins after cell fusion: if different alleles of an homeodomain (HD1) and HD2 protein from the same gene pair interact, this complex will form a heterodimeric transcriptional regulator that stimulates dikaryotic growth.