Plant & Animal Genomes XI Conference

January 11-15, 2003
Town & Country Convention Center
San Diego, CA

Workshop: Apomixis
            

CHARACTERIZATION OF THE GENOMIC REGION ASSOCIATED WITH THE TRANSMISSION OF APOMIXIS IN PENNISETUM AND CENCHRUS

¹ Department of Horticulture, The University of Georgia Tifton Campus, Tifton, GA 31793-0748

² Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843

³ USDA-ARS, Coastal Plain Experiment Station, Tifton, GA 31793-0748

Apomixis, or asexual reproduction through seeds, can occur by several processes, one of which is apospory. Aposporous embryo sacs develop from nucellar cells of the ovule in Cenchrus ciliaris, Pennisetum squamulatum, and several other apomictic Pennisetum species. The aposporous embryo sacs are four-nucleate and require fertilization of the central cell, but not the egg, in order for seed development to be initiated. The parthenogenetically derived embryos preserve the maternal genotype. We have previously shown that apospory is transmitted by a single genomic region (the ASGR) in crosses between sexual and apomictic parents. The ASGR defines a region where recombination is repressed and where sequence divergence with respect to the rest of the genome leads to hemizygosity of numerous segments. Hemizygosity is likely to occur more frequently in non-genic sequences as compared with coding regions. Based on sample sequencing of BACs, we recently have isolated a number of putative genes that can be used to cross-reference the ASGR to model cereal genomes such as rice and sorghum. Sequence data also are informative for comparing the similarity among non-genic regions. Current data suggest that the ASGR is relatively gene poor and the region has favored the accumulation of retrotransposon-like sequences.