Associate Research Scientist University of Georgia Tifton, Georgia
Apomixis, or asexual reproduction through seed, has multiple evolutionary forms. Apospory, one form of apomixis, involves three reproductive components for seed formation: 1) the creation of unrecombined and unreduced embryo sacs, 2) the development of embryos without fertilization of the egg cells, and 3) functional endosperm formation. The Apospory-Specific Genome Region (ASGR) identified within apomictic Cenchrus, Urochloa (Brachiaria) and Megathyrsus (Panicum) species share a conserved AP2-domain transcription factor, ASGR-BabyBoom-Like (ASGR-BBML), whose function is to promote the transition from egg to zygote/embryo without fertilization. ASGR-BBML transgene expression in egg cells of meiotically reduced embryo sacs permits the recovery of haploid embryos and plants in pearl millet, rice and maize. A glucocorticoid receptor-dexamethasone (GR-DEX) conditional expression system in rice enables the action of ASGR-BBML to be switched on only when haploids were desired. The GR-DEX system confirmed that expression/action of ASGR-BBML reduces plant fertility, can lead to improper embryo development and illustrates the complexity intrinsic to seed development.