Plant & Animal Genomes XI Conference

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

Workshop: Apomixis
            

GENOME-WIDE GENETIC VARIABILITY AND DNA SEQUENCE DIVERGENCE ALONG AN ANEUPLOID CHROMOSOME ASSOCIATED WITH APOMIXIS IN THE Arabis holboellii COMPLEX.

¹ IFREMER, Department of Genetics and Pathology, La Tremblade, 17390, France

² Max Planck Institute for Chemical Ecology, Winzerlaerstr 10, Jena, 07745, Germany

The Arabis holboellii complex is composed of sexual and apomictic individuals found throughout western North America. Polyploidy and aneuploidy are associated with apomixis, and we have shown that both these karyotypes have arisen repeatedly and independently during the evolution of this group. This implies that the apomictic phenotype has also been repeatedly expressed from sexual ancestors in different populations, and hence this species complex may exhibit some predisposition for switching from sexual to apomictic reproduction. Our latest data demonstrate that independently derived aneuploid apomicts are always aneuploid for the SAME chromosome. This chromosome is autosomal in origin, but has undergone morphological changes and no longer pairs with its autosomal progenitors during meiosis I. If this chromosome contains some apomixis factor, then the chromosomal region associated with it may be under selective maintenance while the rest of the chromosome degenerates (sensu pseudoautosomal region of the human Y chromosome). We have thus begun comparing DNA sequence divergence between autosomal and aneuploid alleles at loci scattered along regular intervals on the aneuploid chromosome. Our initial data demonstrate levels of sequence divergence which are consistent with the hypothesis of a degenerating aneuploid allele. We will present our data on relative levels of divergence as a function of locus position along the aneuploid chromosome in order to examine its possible influence on the apomictic phenotype.