Plant & Animal Genome IX Conference Plant & Animal Genome IX Conference
Workshop: Apomixis
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Apomixis, or seed-based maternal reproduction, is characterized by abortion of the meiotic pathway and development of aposporous embryo sacs in Pennisetum. Mature aposporous embryo sacs contain up to four unreduced nuclei comprising a uni- or bi-nucleate central cell, one or two synergids, and an egg cell. The egg develops parthenogenetically (without fertilization), but the central cell must be fertilized in order for endosperm to develop (pseudogamy). Multiple aposporous embryo sacs within one ovule are typical in apomictic genotypes. Some are facultative apomicts that also display the development of meiotically reduced embryo sacs and can produce sexually derived progeny. Apospory in this genus is inherited as a single, dominant locus. Sixteen molecular markers have been identified in P. squamulatum that do not segregate from the apomixis locus in a large population that would be expected to produce recombinants. The lack of recombination suggests either considerable sequence or structural divergence between pairing homologs or a location of the locus in a heterochromatic region, perhaps near a centromere. We are addressing these questions as well as the physical size of the locus by a combination of physical mapping methods including BAC contig development and chromosomal in situ hybridization. In addition, the conservation and collinearity of sequences at the apomixis locus in Cenchrus ciliaris, a species closely related to P. squamulatum, is expected to provide a means for converging on candidate apomixis-relevant genomic regions.