A recently silenced, duplicate PgiC locus in Clarkia |
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Authors: | Gottlieb LD; Ford VS |
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Institution: | Section of Evolution and Ecology, University of California, Davis 95616- 8755, USA. ldgottlieb@ucdavis.edu |
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Abstract: | Previous electrophoretic analysis showed that 17 diploid species of the
wildflower Clarkia (Onagraceae) have two cytosolic isozymes of
phosphoglucose isomerase (PGIC; EC 5.3.1.9), whereas 15 other diploid
species have a single PGIC. Molecular studies revealed that the two
isozymes in the former species are encoded by duplicate genes, PgiC1 and
PgiC2, whereas the single isozyme in the latter is always encoded by PgiC1.
Phylogenetic analysis of the nucleotide sequences implied that PgiC2 was
silenced four times independently in the genus. Here we describe a psi
PgiC2 from C. mildrediae, a species in which only PgiC1 is expressed. The
discovery of the psi PgiC2 is significant because it confirms a formal
prediction of the phylogenetic analysis. The psi PgiC2 includes 5,039
nucleotides corresponding to 18 of the 23 exons of PgiC, as well as the
intervening introns and 3' nontranslated region. The absence of an increase
of nucleotide substitutions in its "exons" suggests that the gene was
silenced recently. The present study appears to be the first to establish
that a specific duplicate gene locus regularly expressed in a group of
related plant species has been silenced in one of them. The multiple
independent silencings of PgiC2 suggest that it remained functional but
inessential in ancestral lineages. We discuss the possibility that PgiC2
may have been preserved in these lineages by selection against mutants
causing defective PGIC1- PGIC2 heterodimers.
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