Toward a genomic analysis of the mating type locus of Gonium pectorale (Volvocales, Chlorophyta)

Takashi Hamaji1,2, Patrick J. Ferris3, Ichiro Nishii2, and Hisayoshi Nozaki1

1Department of Biological Sciences, Graduate School of Science, University of Tokyo, 2Frontier Research System, RIKEN, 3Plant Biology Laboratory, Salk Institute.

Gonium pectorale is an isogamous volvocine alga that has flattened 8- or 16-celled colonies. Only one of the two conjugating isogametes of Chlamydomonas reinhardtii has a tubular mating structure (TMS), while G. pectorale has bilateral mating papilla -- each of the two isogametes bears a TMS. C. reinhardtii has a mating type (MT) locus harboring several MT-specific genes involved in mating type determination and/or function of TMS. Studies of the G. pectorale MT locus could be informative with respect to the evolution of anisogamy/oogamy in the Volvocaceae because the ancestral isogamous organism probably had bilateral mating papillae (Nozaki et al. 2000, MPE). As the first step to identify the G. pectorale MT locus, we isolated from G. pectorale the orthologue of the C. reinhardtii mating type-determining minus-dominance (CrMID) gene. This gene (GpMID) and LEUIS are tightly linked, suggesting they may be harbored in a complex MT locus, just as they are in C. reinhardtii (Hamaji et al. 2008, Genetics). Recently, GpMTD1, the orthologue of C. reinhardtii MTD1, involved in minus gamete differentiation, was identified. The minus-specific inheritance and gamete-specific expression of GpMTD1are essentially the same as those of GpMID. These three MT-linked genes will be used for fully characterizing MT loci of both mating types of G. pectorale.

e-mail address of presenting author: takashi@biol.s.u-tokyo.ac.jp