Plant & Animal Genomes XIII Conference Plant & Animal Genomes XIII ConferenceJanuary 15-19, 2005
Town & Country Convention Center
San Diego, CA
John G. Carman1, 2
Gametophytic apomixis involves dedifferentiation of megasporocytes or nucellar cells, eggs, and central cells or polar nuclei. These dedifferentiation events are followed by the classic heterochronies that constitute apomixis: genetically unreduced embryo sac formation, parthenogenesis, and autonomous or pseudogamous endosperm formation. We have bred Sorghum plants that produce unreduced aposporous embryo sacs (from nucellar cells) in > 25% of their ovules. This was achieved by manipulating allelic variability at loci controlling onset timing of megasporogenesis and allelic variability at different loci controlling onset timing of embryo sac formation. Through detailed embryological analyses of parent lines and segregating F2s, we discovered that onset timing of each major germline development sequence (GDS) event is influenced by unique sets of heterochrony genes. Progress toward mapping these genes will be discussed. Aside from nutrient dependency, the onset of major GDS events appears to be largely independent of temporal developmental milestones occurring in nearby sporophytic tissues (funiculus, chalaza, nucellus, integuments). Also aside from nutrient dependency, onset timing of early embryony appears to be largely independent of temporal developmental milestones occurring in nearby gametophytic tissues (antipodals, polar nuclei, endosperm). The discovery of these developmental independencies and their genetic variability bodes well for the future creation of apomictic plants by conventional breeding or genetic engineering.