DOYLE, JEFF J.1*, RAYMOND H. MAK1, JASON T. RAUSCHER1, and JULIE M. VOGEL2. 1L. H. Bailey Hortorium, Department of Plant Biology, 462 Mann Library Building, Cornell University, Ithaca, NY 14853; 2DuPont Agricultural Biotechnology, Genome Sciences, Del Tech Park, Suite 200, PO Box 6104, Newark, DE 19714-6104. - The evolution of gene expression in a wild soybean polyploid complex: conventional and genomics approaches.
There is relatively little published information on the evolution of
gene expression in polyploids, particularly outside of model groups
such as maize, wheat, Brassica, and Arabidopsis. Our
work on the systematics of allopolyploids in the wild perennial
relatives of soybean (Glycine subgenus Glycine) provides
us with the knowledge of genome origins that is required for testing
hypotheses of gene and genome evolution. We have sought evidence of
gene silencing in these recently formed polyploids. Initially we
adopted a gene-by-gene approach, choosing classes of genes we felt
were candidates for silencing. The 18S-26S nuclear ribosomal gene
family was chosen because nucleolar dominance is well-documented from
model allopolyploids. Ribosomal genes are differentially expressed in
at least some Glycine allopolyploids, both in cases where there are
great differences in copy number between homoeologous repeats and
where homoeologous copy number is approximately equal. The
chloroplast-expressed nuclear-encoded isozyme of glutamine synthetase
was chosen as an example of a nuclear gene functioning in the
maternally-inherited chloroplast. However, we found no evidence of
silencing. This led us to adopt a genomics approach to searching for
silenced genes. We isolated a potentially methylated DNA fraction from
allopolyploids and their diploid progenitors, and used this fraction
to probe filters containing 2,300 unique Glycine max cDNA clones.
Hybridization patterns were very similar both among diploids from
different genome groups and from polyploids, suggesting that few, if
any, homoeologous copies of genes are methylated in Glycine
allopolyploids.
Key words: gene expression, genomics, Glycine subgenus Glycine, homoeologous gene silencing, nuclear ribosomal genes, polyploidy