Plant & Animal Genomes XV Conference Plant & Animal Genomes XV ConferenceJanuary 13-17, 2007
Town & Country Convention Center
San Diego, CA
John G. Carman1, 2 , Dominique Roche1
In some fungi, jellyfish, flatworms, parasitic flukes, roundworms, nematodes, rotifers, gastrotrichs, snails, worms, brine shrimp, insects, fish, slime molds, paramecium, diatoms, red, brown and green algae, ferns and angiosperms, mechanisms have evolved that replace meiosis with apomeiosis wherein unreduced (2n) spores or gametes form. Sooner or later, a zygote-like cell develops there from, which continues the life cycle parthenogenically. In ferns and angiosperms, 2n gametes may also form aposporously, in which case the germline aborts. The rarity of apomixis among kingdoms and the apparent hybrid nature of most apomicts have suggested to many that apomixis is derived from amphimixis. We present a strikingly different interpretation, which is based on two observations. First, the cytological mechanisms responsible for apomixis are in many cases identical across kingdoms. Second, new molecular phylogenies now link primitive unicellular eukaryotic apomicts (protists) with more derived multicellular apomicts. These observations raise interesting questions concerning the age of the phenomenon of apomixis itself and suggest: i) apomixis is ephemeral, having appeared and disappeared in certain lineages repeatedly during deep time evolution, and ii) certain mechanisms of apomixis may be extremely ancient, possibly coevolving with and impeding the evolution of sex itself. Functional aspects of these latter mechanisms of apomixis may represent molecular vestiges of mitotic reproduction mechanisms that predate amphimixis, i.e. they may represent asexual default pathways that function when sex (chromosome reduction and syngamy) is genetically or epigenetically disturbed by hybridization and polyploidization.