Abstract Detail

Systematics Section / ASPT

Pfeil, Bernard E. [1], Schlueter, Jessica A. [2], Shoemaker, Randy C. [3], Doyle, Jeff J. [1].

Is your nuclear gene telling the truth? A case study in legmues that tests when polyploidy occurred relative to taxon divergence.

Young polyploid events can be confidently diagnosed by a combination of increased chromosome number, duplication of linkage groups with preserved synteny, and phylogenetic analysis of homoeologous genes. As little change occurs after the polyploid event, the inference of polyploidy is often straight forward. However, older polyploid events may become increasingly difficult to identify as various processes complicate these methods of inferring past genomic events. From a phylogenetic perspective, processes that may affect any one gene and potentially mislead investigators will not affect all genes, and will not affect genes in the same way. Thus a multigene approach, made possible by the increase in genomic-scale sequence data becoming available, should have the power to overcome these difficulties and allow us to infer genomic events further into the past. A previous study using duplicated genes in legume model species showed that Glycine and Medicago each have a large scale round of correlated gene duplications, estimated to have occurred at c. 44 and 58 Mya respectively, likely due to polyploidy. However, uncertainties in molecular dating methods do not clearly indicate whether these taxa have undergone polyploidy independently or whether they share a paleopolyploid event. We used 39 nuclear gene families with three or four members in Glycine to show that phylogenetic methods can discriminate between these hypotheses and show that these taxa share this paleopolyploid event. Individual gene trees were subjected to analysis of synonymous rates between sequence pairs. This analysis revealed that some gene trees were misleading despite having topological support for either of the two hypotheses. Only 41% of genes examined support either hypothesis, highlighting the need for a multigene approach when studying ancient events with nDNA.

1 - Cornell University, L.H. Bailey Hortorium, Department of Plant Biology, Ithaca, New York, 14853, U.S.A.
2 - Iowa State University, Genetics, Development and Cell Biology, Ames, Iowa, 50011, USA
3 - USDA-ARS-CICGR, Iowa State University, USDA ARS CICGR and Agronomy, Ames, Iowa, 50011, USA

Keywords:
Fabaceae
Glycine
Leguminosae
phylogenetics
polyploidy
nDNA
Medicago
synonymous distance.

Presentation Type: Paper
Session: 58-8
Location: Cottonwood B (Snowbird Center)
Date: Wednesday, August 4th, 2004
Time: 3:15 PM
Abstract ID:289