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MOLECULAR CHARACTERIZATION OF PgiC IN A TETRAPLOID PLANT AND ITS DIPLOID RELATIVES
1Section of Evolution and Ecology, Division of Biological Sciences, University of California, Davis, California, 95616.
Summary
In allotetraploid plants, homologous genes are expressed, not silenced. The PgiC2 gene in Clarkia gracilis is active, a rare case of an expressed gene in a tetraploid not found in its diploid relatives.
Area of Science:
- Plant genetics
- Molecular evolution
- Polyploidy research
Background:
- Allotetraploid species combine genomes from related diploids, but gene expression and evolution in this new context are poorly understood.
- Gene silencing is a potential outcome of polyploidy, yet molecular evidence in enzyme-encoding genes is scarce.
- The phosphoglucose isomerase (PGI) gene family, specifically PgiC, provides a model to study gene expression and evolution in polyploids.
Purpose of the Study:
- To investigate the expression, interaction, and evolution of homologous PgiC genes in the allotetraploid Clarkia gracilis and its diploid relatives.
- To determine if gene silencing occurs in the PgiC genes within the tetraploid nucleus.
- To characterize the PgiC gene repertoire and expression patterns in C. gracilis, particularly the unexpected presence of an active PgiC2.
Main Methods:
- Reverse-transcriptase polymerase chain reaction (RT-PCR) was used to assess gene expression from seedling leaf mRNA.
- Sequence analysis was employed to compare gene evolution rates and intron-exon structures.
- Parsimony analysis was utilized for phylogenetic placement of extinct gene donors.
Main Results:
- Clarkia gracilis possesses three active PgiC genes: two PgiC1 copies and one PgiC2 copy.
- All three PgiC genes in C. gracilis are expressed, with similar evolutionary rates and intron-exon structures to their diploid homologues.
- An expressed PgiC2 locus in C. gracilis is active, despite being silenced in its diploid relatives, including a presumed extinct donor species.
Conclusions:
- Contrary to expectations, homologous PgiC genes are not silenced in the allotetraploid C. gracilis.
- The active PgiC2 in C. gracilis represents the first documented instance of an active gene locus in a tetraploid that is no longer expressed in its diploid progenitors.
- Gene conversion may have occurred in diploid ancestors, but no PgiC genes active at the origin of C. gracilis have been silenced.
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