SEQUENCING OF ONION DNA REVEALS STRONG DIFFERENCES BETWEEN THE ALLIUMS AND THE GRASSES

Michael J. Havey, Joseph C. Kuhl, Foo Cheung, Qiaoping Yuan, William Martin, Yayeh Zewdie, John McCallum, Andrew Catanach, Paul Rutherford, Kenneth C. Sink, Maria Jenderek, James P. Prince, and Christopher D. Town

USDA-ARS and University of Wisconsin, Department of Horticulture, 1575 Linden Drive, University of Wisconsin, Madison, WI 53706. Phone: 608-262-1830; Fax: 608-262-4743; Email: mjhavey@wisc.edu.

The Alliums (onion, garlic, leek, etc.) are members of the order Asparagales, which is sister to the order Poales (the grasses). Enormous genetic resources have been developed for the grasses and some researchers have proposed that the DNA of grasses is representative of all monocots. To determine if DNA differences exit between the Asparagales and Poales, we generated 11,008 unique expressed sequence tags (ESTs) from a normalized cDNA library of onion. Sequence analyses of these ESTs revealed simple sequence repeats (SSRs) and single nucleotide polymorphisms (SNPs). Mean nucleotide similarity between rice (as a representative of the grasses) and onion was 78% across coding regions. Expressed sequence and genomic DNA comparisons revealed strong differences between the Asparagales and Poales for GC content and distribution, indicating that genomic characteristics are not uniform across the monocots. The Asparagales were more similar to eudicots than the Poales for important DNA characteristics.

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