XVI International Botanical Congess

Genes involved in sex determination are often contained within genomic regions of suppressed recombination and linked to genes involved in mating functions, a phenomenon familiar from the dimorphic sex chromosomes of animals. Our characterization of the mating type (mt) loci of Chlamydomonas demonstrates that such genomic regions can evolve even in a haploid unicellular organism. The C. reinhardtii mt locus is a ~1 Mb non-recombining region. The sex-determining mid gene is found only in the mt- locus, while the gamete fusion gene, fus1, is found only in the mt+ locus. Among the transcripts within the mt loci, some correspond to housekeeping genes while others are involved in mating and zygote formation. One of the latter is a 12 kb message that encodes the minus agglutinin -- a hydroxyproline-rich glycoprotein on the surface of gametic flagella that mediates the initial adhesion between mating gametes.