Plant & Animal Genomes XIII Conference

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

FISH And Meiotic Characterization Of Apomictic Boechera Clones

Hans de Jong¹ , Laksana Kantama² , Song-Bin Chang¹ , Tim Sharbel³ , Thomas Mitchell-Olds⁴ , Eric Schranz⁴

¹  Laboratory of Genetics, Wageningen University, Arboretumlaan 4, 6703 BD Wageningen, The Netherlands

²  Laboratory of Biochemistry, Wageningen University, Dreijenlaan 3, 6703 HA Wageningen, The Netherlands

³  Institute of Plant Genetics and Crop Plant Research (IPK), Gatersleben, Germany

⁴  Max-Planck-Institut für Chemische Ökologie, 07745 Jena, Germany

Our study on apomictic clones in the Boechera holboellii complex focussed on B-chromosomes pre-sent in several aneuploid (2n=15; 21 and 22) apomictic lineages. Previous studies revealed that such apomicts share a specific a specific chromosomal region in aneuploid dosage, suggesting that the B contains apomixis specific DNA sequences. We now investigate whether and how this chromosome controls apomixis. DAPI karyotype analyses of various apomicts showed that the extra chromosome is heterochromatic and different between the clones, and so shares properties of a B chromosome. FISH with probes from rDNA repeats, and five Arabidopsis BACs with apo-mixis related genes from natural apomicts (B. holboellii, Poa and Paspalum) showed no signals on the B, but did indicate structural karyotype heterozygosity. Genomic in situ hybridization (GISH) with DNA of the sexual B. drummondii hybridized to the B chromosome aneuploids demonstrated that this extra chromosome is largely composed of unique repetitive sequences not or hardly present on the A chromosomes. The B at meiotic metaphase appeared as a laggard, but more often associated one of the A bivalents, which may indicate that the clones are evolutionary relatively young or under selective maintenance, but the wide geographic distribution of the Bs contradicts the idea that they are young. Further analysis in apomictic plants identified as B. divaricarpa showed asynaptic meiosis with irregular pachytene and merely univalents at metaphase I, suggesting that this species is an allodiploid which arose via hybridization between a sexual diploid B. drummondii and an aneuploid apomictic B. holboellii.