Bipolar and Tetrapolar Mating Systems in the Ustilaginales

Abstract

This chapter discusses species that include Ustilago hordei in particular, that have provided useful comparative information leading to insights into the genetic basis of bipolar versus tetrapolar mating systems in the smut fungi as a group. It first discusses the importance of smut fungi and the interactions of these pathogens with host plants to provide context for appreciating the role of mating in disease. The chapter then focus on the details of the mating system in U. hordei, including the structure and function of the mating-type loci, the genomic organization of these elements, and the sequence of the 527-kb MAT-1 locus. The cloning and analysis of the b genes from U. hordei revealed that they are very similar in structure to those in U. maydis, consisting of a gene complex with divergently transcribed bE and bW genes. The large size of the U. hordei MAT region and the suppression of recombination in this area prompted the authors to propose that the region might function to maintain a set of genes that function together in sexual development and, potentially, in pathogenesis. They therefore characterized t.