Plant & Animal Genomes XIII Conference

January 15-19, 2005
Town & Country Convention Center
San Diego, CA

Physical And Functional Characteristics Of The Genomic Region Associated With Apomixis In Pennisetum

Peggy Ozias-Akins¹ , Joann A. Conner¹ , Shailendra Goel¹ , Yukio Akiyama¹ , Marie-Michele Cordonnier-Pratt² , Chun Liang² , Lee H. Pratt² , Wayne W. Hanna³

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

²  University of Georgia, Department of Plant Biology, Athens, GA 30602

³  University of Georgia Tifton Campus, Department of Crop and Soil Science, Tifton, GA 31793-0748 USA

Apomixis, or asexual reproduction through seeds, takes the form of apospory in the genus Pennisetum. Aposporous embryo sacs develop mitotically from nucellar cells within the ovule followed by parthenogenesis of chromosomally unreduced eggs. Apomixis has been genetically mapped in Pennisetum squamulatum to the distal end of a single linkage group. Physical mapping has confirmed that a single chromosome from P. squamulatum is necessary and sufficient to transmit apomixis to backcrosses with pearl millet (P. glaucum). This chromosome is termed the ASGR (apospory-specific genomic region)-carrier chromosome. Bacterial artificial chromosome (BAC) clones containing apomixis-linked markers have been isolated and physically mapped, both as fingerprinted contigs (FPC) and by flurorescence in situ hybridization (FISH). FISH has demonstrated that the long arm of the ASGR-carrier chromosome is heteromorphic, highly hemizygous, and contains abundant retrotransposons, three characteristics which likely contribute to the lack of recombination at the ASGR. DNA sequence has been obtained from 36 BACs (~0.5x coverage with shotgun libraries) and has allowed the discovery of apomixis-linked genes, although at low density. Based on these gene sequences, localized regions of microsynteny with rice exist, but macrosynteny is disjointed. More complete sequencing of 17 genes revealed a high level of gene duplication within the region. Gene predictions indicate that most of the genes have the potential to be functional. Gene expression analysis currently is underway.