Evolution of an expanded sex determining region in Volvox
Patrick Ferris1, Bradley J.S.C. Olson1, Peter L. De Hoff1, Stephen Douglass2, David Casero Diaz-Cano2, Simon Prochnik3, Sa Geng1, Rhitu Rai1,4, Jane Grimwood5, Jeremy Schmutz5, Ichiro Nishii6, Takashi Hamaji7, Hisayoshi Nozaki7, Matteo Pellegrini2,and James G. Umen1
1) The Salk Institute for Biological Studies, La Jolla, California 92037, USA
2) Institute for Genomics and Proteomics and Department of Molecular, Cell and Developmental Biology, University of California, Los Angeles, California, 90095, USA
3) U.S. Department of Energy (DOE) Joint Genome Institute (JGI), Walnut Creek, California, 95498, USA
4) Laboratory of Plant Microbe Interaction, National Research Center on Plant Biotechnology, Pusa Campus, Indian Agricultural Research Institute, New Delhi-110012, India
5) Genome Sequencing Center, Hudson Alpha Institute for Biotechnology, Huntsville, Alabama, 35906, USA
6) Department of Biological Science, Nara Women's University, Nara 630-8506, Japan
7) Department of Biological Sciences, University of Tokyo, Tokyo 113-0033, Japan
Although dimorphic sexes have evolved repeatedly in multicellular eukaryotes, their origins are unknown. The mating locus (MT) of the sexually dimorphic multicellular green alga, Volvox carteri, specifies the production of eggs and sperm and has undergone a remarkable expansion and divergence relative to MT from Chlamydomonas reinhardtii. Transcriptome analysis revealed a rewired gametic expression program for Volvox MT genes relative to Chlamydomonas, and identified multiple new gender-specific and sex-regulated transcripts. The retinoblastoma tumor suppressor homolog MAT3 is a Volvox MT gene that displays sexually regulated alternative splicing and evidence of gender-specific selection, both indicative of cooption into the sexual cycle. The accelerated divergence of sex chromosomes is usually associated with gene loss and degeneration. Our data suggest that expansion, loss of recombination, and rapid divergence can be mutually reinforcing properties of sex determining regions that facilitate cooption into the sexual cycle and provide novel sources of developmental innovation.
e-mail address of presenting author: umen@salk.edu
web site: http://pbio.salk.edu/pbiou