PAG-XIII  Plant & Animal Genomes XIII Conference

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


W015 : Apomixis

A Population Genetic Approach To Identifying The Apomixis Factor In The Boechera holboellii Complex

Timothy F. Sharbel1 , Thomas Mitchell-Olds2

1  Apomixis Research Group, Dept. of Cytogenetics, Institut für Pflanzengenetik und Kulturpflanzenforschung (IPK), Corrensstraße 3, D-06466, Gatersleben, Germany
2  Max Planck Institut für Chemische Ökologie, Beutenberg Campus Winzerlaer Str. 10, D-07745 Jena, Germany

The Boechera holboellii complex comprises B. holboellii and B. drummondii, both of which can reproduce through sex or apomixis. Sexuality is associated with diploidy, whereas apomictic individuals can be diploid or triploid, with or without B chromosomes. Both diploid and triploid karyotypes are found in multiple chloroplast haplotypes of both species, and hence triploidy has originated multiple times during the evolution of this complex. B chromosome carriers are found in geographically and genetically distinct populations, and it is unknown whether the extra chromosomes are shared by common descent (single origin) or have originated via genomic processes associated with the repeated transition from diploidy to triploidy. Diploid plants containing the Bs reproduce apomictically, suggesting that the supernumerary elements are associated with apomixis. Finally, our analyses of pollen size and viability suggest that irregular chromosome segregation in some triploid lineages may lead to the generation of diploid individuals which carry the B chromosomes. Repeated origins of B chromosomes and polyploidy may imply that the apomictic phenotype has also been attained multiple times during the evolution of this complex. Analyses of autosomal single nucleotide polymorphisms (SNP) and microsatellites show that apomictic members of the B. holboellii complex demonstrate as much, if not more, genetic variability relative to their sexual counterparts. The nature and genomic distribution of this variability will be discussed in light of our approach to identifying factors which have led to apomixis expression.